diff --git a/src/ol/render/webgl/webglreplay.js b/src/ol/render/webgl/webglreplay.js
index 3d1f743139..4516f8ce4a 100644
--- a/src/ol/render/webgl/webglreplay.js
+++ b/src/ol/render/webgl/webglreplay.js
@@ -233,8 +233,10 @@ ol.render.webgl.ImageReplay.prototype.getDeleteResourcesFunction =
   // be used by other ImageReplay instances (for other layers). And
   // they will be deleted when disposing of the ol.webgl.Context
   // object.
-  goog.asserts.assert(!goog.isNull(this.verticesBuffer_));
-  goog.asserts.assert(!goog.isNull(this.indicesBuffer_));
+  goog.asserts.assert(!goog.isNull(this.verticesBuffer_),
+      'verticesBuffer must not be null');
+  goog.asserts.assert(!goog.isNull(this.indicesBuffer_),
+      'indicesBuffer must not be null');
   var verticesBuffer = this.verticesBuffer_;
   var indicesBuffer = this.indicesBuffer_;
   var textures = this.textures_;
@@ -272,18 +274,19 @@ ol.render.webgl.ImageReplay.prototype.drawAsync = goog.abstractMethod;
  */
 ol.render.webgl.ImageReplay.prototype.drawCoordinates_ =
     function(flatCoordinates, offset, end, stride) {
-  goog.asserts.assert(goog.isDef(this.anchorX_));
-  goog.asserts.assert(goog.isDef(this.anchorY_));
-  goog.asserts.assert(goog.isDef(this.height_));
-  goog.asserts.assert(goog.isDef(this.imageHeight_));
-  goog.asserts.assert(goog.isDef(this.imageWidth_));
-  goog.asserts.assert(goog.isDef(this.opacity_));
-  goog.asserts.assert(goog.isDef(this.originX_));
-  goog.asserts.assert(goog.isDef(this.originY_));
-  goog.asserts.assert(goog.isDef(this.rotateWithView_));
-  goog.asserts.assert(goog.isDef(this.rotation_));
-  goog.asserts.assert(goog.isDef(this.scale_));
-  goog.asserts.assert(goog.isDef(this.width_));
+  goog.asserts.assert(goog.isDef(this.anchorX_), 'anchorX is defined');
+  goog.asserts.assert(goog.isDef(this.anchorY_), 'anchorY is defined');
+  goog.asserts.assert(goog.isDef(this.height_), 'height is defined');
+  goog.asserts.assert(goog.isDef(this.imageHeight_), 'imageHeight is defined');
+  goog.asserts.assert(goog.isDef(this.imageWidth_), 'imageWidth is defined');
+  goog.asserts.assert(goog.isDef(this.opacity_), 'opacity is defined');
+  goog.asserts.assert(goog.isDef(this.originX_), 'originX is defined');
+  goog.asserts.assert(goog.isDef(this.originY_), 'originY is defined');
+  goog.asserts.assert(goog.isDef(this.rotateWithView_),
+      'rotateWithView is defined');
+  goog.asserts.assert(goog.isDef(this.rotation_), 'rotation is defined');
+  goog.asserts.assert(goog.isDef(this.scale_), 'scale is defined');
+  goog.asserts.assert(goog.isDef(this.width_), 'width is defined');
   var anchorX = this.anchorX_;
   var anchorY = this.anchorY_;
   var height = this.height_;
@@ -464,10 +467,12 @@ ol.render.webgl.ImageReplay.prototype.finish = function(context) {
   var gl = context.getGL();
 
   this.groupIndices_.push(this.indices_.length);
-  goog.asserts.assert(this.images_.length === this.groupIndices_.length);
+  goog.asserts.assert(this.images_.length === this.groupIndices_.length,
+      'number of images and groupIndices match');
   this.hitDetectionGroupIndices_.push(this.indices_.length);
   goog.asserts.assert(this.hitDetectionImages_.length ===
-      this.hitDetectionGroupIndices_.length);
+      this.hitDetectionGroupIndices_.length,
+      'number of hitDetectionImages and hitDetectionGroupIndices match');
 
   // create, bind, and populate the vertices buffer
   this.verticesBuffer_ = new ol.webgl.Buffer(this.vertices_);
@@ -488,12 +493,14 @@ ol.render.webgl.ImageReplay.prototype.finish = function(context) {
   var texturePerImage = {};
 
   this.createTextures_(this.textures_, this.images_, texturePerImage, gl);
-  goog.asserts.assert(this.textures_.length === this.groupIndices_.length);
+  goog.asserts.assert(this.textures_.length === this.groupIndices_.length,
+      'number of textures and groupIndices match');
 
   this.createTextures_(this.hitDetectionTextures_, this.hitDetectionImages_,
       texturePerImage, gl);
   goog.asserts.assert(this.hitDetectionTextures_.length ===
-      this.hitDetectionGroupIndices_.length);
+      this.hitDetectionGroupIndices_.length,
+      'number of hitDetectionTextures and hitDetectionGroupIndices match');
 
   this.anchorX_ = undefined;
   this.anchorY_ = undefined;
@@ -524,7 +531,8 @@ ol.render.webgl.ImageReplay.prototype.finish = function(context) {
  */
 ol.render.webgl.ImageReplay.prototype.createTextures_ =
     function(textures, images, texturePerImage, gl) {
-  goog.asserts.assert(textures.length === 0);
+  goog.asserts.assert(textures.length === 0,
+      'upon creation, textures is empty');
 
   var texture, image, uid, i;
   var ii = images.length;
@@ -571,11 +579,13 @@ ol.render.webgl.ImageReplay.prototype.replay = function(context,
   var gl = context.getGL();
 
   // bind the vertices buffer
-  goog.asserts.assert(!goog.isNull(this.verticesBuffer_));
+  goog.asserts.assert(!goog.isNull(this.verticesBuffer_),
+      'verticesBuffer must not be null');
   context.bindBuffer(goog.webgl.ARRAY_BUFFER, this.verticesBuffer_);
 
   // bind the indices buffer
-  goog.asserts.assert(!goog.isNull(this.indicesBuffer_));
+  goog.asserts.assert(!goog.isNull(this.indicesBuffer_),
+      'indecesBuffer must not be null');
   context.bindBuffer(goog.webgl.ELEMENT_ARRAY_BUFFER, this.indicesBuffer_);
 
   var useColor = brightness || contrast != 1 || hue || saturation != 1;
@@ -699,7 +709,8 @@ ol.render.webgl.ImageReplay.prototype.replay = function(context,
  */
 ol.render.webgl.ImageReplay.prototype.drawReplay_ =
     function(gl, context, skippedFeaturesHash, textures, groupIndices) {
-  goog.asserts.assert(textures.length === groupIndices.length);
+  goog.asserts.assert(textures.length === groupIndices.length,
+      'number of textures and groupIndeces match');
   var elementType = context.hasOESElementIndexUint ?
       goog.webgl.UNSIGNED_INT : goog.webgl.UNSIGNED_SHORT;
   var elementSize = context.hasOESElementIndexUint ? 4 : 2;
@@ -873,7 +884,8 @@ ol.render.webgl.ImageReplay.prototype.drawHitDetectionReplayOneByOne_ =
     function(gl, context, skippedFeaturesHash, featureCallback,
     opt_hitExtent) {
   goog.asserts.assert(this.hitDetectionTextures_.length ===
-      this.hitDetectionGroupIndices_.length);
+      this.hitDetectionGroupIndices_.length,
+      'number of hitDetectionTextures and hitDetectionGroupIndices match');
   var elementType = context.hasOESElementIndexUint ?
       goog.webgl.UNSIGNED_INT : goog.webgl.UNSIGNED_SHORT;
   var elementSize = context.hasOESElementIndexUint ? 4 : 2;
@@ -923,27 +935,31 @@ ol.render.webgl.ImageReplay.prototype.setFillStrokeStyle = goog.abstractMethod;
  */
 ol.render.webgl.ImageReplay.prototype.setImageStyle = function(imageStyle) {
   var anchor = imageStyle.getAnchor();
-  goog.asserts.assert(!goog.isNull(anchor));
+  goog.asserts.assert(!goog.isNull(anchor), 'imageStyle anchor is not null');
   var image = imageStyle.getImage(1);
-  goog.asserts.assert(!goog.isNull(image));
+  goog.asserts.assert(!goog.isNull(image), 'imageStyle image is not null');
   var imageSize = imageStyle.getImageSize();
-  goog.asserts.assert(!goog.isNull(imageSize));
+  goog.asserts.assert(!goog.isNull(imageSize),
+      'imageStyle imageSize is not null');
   var hitDetectionImage = imageStyle.getHitDetectionImage(1);
-  goog.asserts.assert(!goog.isNull(hitDetectionImage));
+  goog.asserts.assert(!goog.isNull(hitDetectionImage),
+      'imageStyle hitDetectionImage is not null');
   var hitDetectionImageSize = imageStyle.getHitDetectionImageSize();
-  goog.asserts.assert(!goog.isNull(hitDetectionImageSize));
+  goog.asserts.assert(!goog.isNull(hitDetectionImageSize),
+      'imageStyle hitDetectionImageSize is not null');
   var opacity = imageStyle.getOpacity();
-  goog.asserts.assert(goog.isDef(opacity));
+  goog.asserts.assert(goog.isDef(opacity), 'imageStyle opacity is defined');
   var origin = imageStyle.getOrigin();
-  goog.asserts.assert(!goog.isNull(origin));
+  goog.asserts.assert(!goog.isNull(origin), 'imageStyle origin is not null');
   var rotateWithView = imageStyle.getRotateWithView();
-  goog.asserts.assert(goog.isDef(rotateWithView));
+  goog.asserts.assert(goog.isDef(rotateWithView),
+      'imageStyle rotateWithView is defined');
   var rotation = imageStyle.getRotation();
-  goog.asserts.assert(goog.isDef(rotation));
+  goog.asserts.assert(goog.isDef(rotation), 'imageStyle rotation is defined');
   var size = imageStyle.getSize();
-  goog.asserts.assert(!goog.isNull(size));
+  goog.asserts.assert(!goog.isNull(size), 'imageStyle size is not null');
   var scale = imageStyle.getScale();
-  goog.asserts.assert(goog.isDef(scale));
+  goog.asserts.assert(goog.isDef(scale), 'imageStyle scale is defined');
 
   var currentImage;
   if (this.images_.length === 0) {
@@ -952,7 +968,8 @@ ol.render.webgl.ImageReplay.prototype.setImageStyle = function(imageStyle) {
     currentImage = this.images_[this.images_.length - 1];
     if (goog.getUid(currentImage) != goog.getUid(image)) {
       this.groupIndices_.push(this.indices_.length);
-      goog.asserts.assert(this.groupIndices_.length === this.images_.length);
+      goog.asserts.assert(this.groupIndices_.length === this.images_.length,
+          'number of groupIndices and images match');
       this.images_.push(image);
     }
   }
@@ -965,7 +982,8 @@ ol.render.webgl.ImageReplay.prototype.setImageStyle = function(imageStyle) {
     if (goog.getUid(currentImage) != goog.getUid(hitDetectionImage)) {
       this.hitDetectionGroupIndices_.push(this.indices_.length);
       goog.asserts.assert(this.hitDetectionGroupIndices_.length ===
-          this.hitDetectionImages_.length);
+          this.hitDetectionImages_.length,
+          'number of hitDetectionGroupIndices and hitDetectionImages match');
       this.hitDetectionImages_.push(hitDetectionImage);
     }
   }
@@ -1066,7 +1084,8 @@ ol.render.webgl.ReplayGroup.prototype.getReplay =
   var replay = this.replays_[replayType];
   if (!goog.isDef(replay)) {
     var constructor = ol.render.webgl.BATCH_CONSTRUCTORS_[replayType];
-    goog.asserts.assert(goog.isDef(constructor));
+    goog.asserts.assert(goog.isDef(constructor),
+        'a constructor could be found in ol.render.webgl.BATCH_CONSTRUCTORS_');
     replay = new constructor(this.tolerance_, this.maxExtent_);
     this.replays_[replayType] = replay;
   }
diff --git a/src/ol/renderer/canvas/canvasimagelayerrenderer.js b/src/ol/renderer/canvas/canvasimagelayerrenderer.js
index d5cb82c7a4..ee3d0bba4d 100644
--- a/src/ol/renderer/canvas/canvasimagelayerrenderer.js
+++ b/src/ol/renderer/canvas/canvasimagelayerrenderer.js
@@ -156,7 +156,8 @@ ol.renderer.canvas.ImageLayer.prototype.prepareFrame =
 
   var image;
   var imageLayer = this.getLayer();
-  goog.asserts.assertInstanceof(imageLayer, ol.layer.Image);
+  goog.asserts.assertInstanceof(imageLayer, ol.layer.Image,
+      'layer is an instance of ol.layer.Image');
   var imageSource = imageLayer.getSource();
 
   var hints = frameState.viewHints;
@@ -172,7 +173,8 @@ ol.renderer.canvas.ImageLayer.prototype.prepareFrame =
     var projection = viewState.projection;
     var sourceProjection = imageSource.getProjection();
     if (!goog.isNull(sourceProjection)) {
-      goog.asserts.assert(ol.proj.equivalent(projection, sourceProjection));
+      goog.asserts.assert(ol.proj.equivalent(projection, sourceProjection),
+          'projection and sourceProjection are equivalent');
       projection = sourceProjection;
     }
     image = imageSource.getImage(
diff --git a/src/ol/renderer/canvas/canvaslayerrenderer.js b/src/ol/renderer/canvas/canvaslayerrenderer.js
index 21d0d23c90..137485307f 100644
--- a/src/ol/renderer/canvas/canvaslayerrenderer.js
+++ b/src/ol/renderer/canvas/canvaslayerrenderer.js
@@ -50,7 +50,8 @@ ol.renderer.canvas.Layer.prototype.composeFrame =
     var extent = layerState.extent;
     var clipped = goog.isDef(extent);
     if (clipped) {
-      goog.asserts.assert(goog.isDef(extent));
+      goog.asserts.assert(goog.isDef(extent),
+          'layerState extent is defined');
       var pixelRatio = frameState.pixelRatio;
       var topLeft = ol.extent.getTopLeft(extent);
       var topRight = ol.extent.getTopRight(extent);
diff --git a/src/ol/renderer/canvas/canvasmaprenderer.js b/src/ol/renderer/canvas/canvasmaprenderer.js
index 2074a898ad..86b1c06512 100644
--- a/src/ol/renderer/canvas/canvasmaprenderer.js
+++ b/src/ol/renderer/canvas/canvasmaprenderer.js
@@ -83,7 +83,7 @@ ol.renderer.canvas.Map.prototype.createLayerRenderer = function(layer) {
   } else if (ol.ENABLE_VECTOR && layer instanceof ol.layer.Vector) {
     return new ol.renderer.canvas.VectorLayer(layer);
   } else {
-    goog.asserts.fail();
+    goog.asserts.fail('unexpected layer configuration');
     return null;
   }
 };
@@ -138,7 +138,8 @@ ol.renderer.canvas.Map.prototype.dispatchComposeEvent_ =
  */
 ol.renderer.canvas.Map.prototype.getCanvasLayerRenderer = function(layer) {
   var layerRenderer = this.getLayerRenderer(layer);
-  goog.asserts.assertInstanceof(layerRenderer, ol.renderer.canvas.Layer);
+  goog.asserts.assertInstanceof(layerRenderer, ol.renderer.canvas.Layer,
+      'layerRenderer is an instance of ol.renderer.canvas.Layer');
   return /** @type {ol.renderer.canvas.Layer} */ (layerRenderer);
 };
 
@@ -185,7 +186,8 @@ ol.renderer.canvas.Map.prototype.renderFrame = function(frameState) {
     layerState = layerStatesArray[i];
     layer = layerState.layer;
     layerRenderer = this.getLayerRenderer(layer);
-    goog.asserts.assertInstanceof(layerRenderer, ol.renderer.canvas.Layer);
+    goog.asserts.assertInstanceof(layerRenderer, ol.renderer.canvas.Layer,
+        'layerRenderer is an instance of ol.renderer.canvas.Layer');
     if (!ol.layer.Layer.visibleAtResolution(layerState, viewResolution) ||
         layerState.sourceState != ol.source.State.READY) {
       continue;
diff --git a/src/ol/renderer/canvas/canvastilelayerrenderer.js b/src/ol/renderer/canvas/canvastilelayerrenderer.js
index ccf1db3d2e..7c6bc6d77b 100644
--- a/src/ol/renderer/canvas/canvastilelayerrenderer.js
+++ b/src/ol/renderer/canvas/canvastilelayerrenderer.js
@@ -182,7 +182,8 @@ ol.renderer.canvas.TileLayer.prototype.prepareFrame =
   var projection = viewState.projection;
 
   var tileLayer = this.getLayer();
-  goog.asserts.assertInstanceof(tileLayer, ol.layer.Tile);
+  goog.asserts.assertInstanceof(tileLayer, ol.layer.Tile,
+      'layer is an instance of ol.layer.Tile');
   var tileSource = tileLayer.getSource();
   var tileGrid = tileSource.getTileGridForProjection(projection);
   var tileGutter = tileSource.getGutter();
@@ -218,9 +219,12 @@ ol.renderer.canvas.TileLayer.prototype.prepareFrame =
 
   var canvas, context;
   if (goog.isNull(this.canvas_)) {
-    goog.asserts.assert(goog.isNull(this.canvasSize_));
-    goog.asserts.assert(goog.isNull(this.context_));
-    goog.asserts.assert(goog.isNull(this.renderedCanvasTileRange_));
+    goog.asserts.assert(goog.isNull(this.canvasSize_),
+        'canvasSize is null (because canvas is null)');
+    goog.asserts.assert(goog.isNull(this.context_),
+        'context is null (because canvas is null)');
+    goog.asserts.assert(goog.isNull(this.renderedCanvasTileRange_),
+        'renderedCanvasTileRange is null (because canvas is null)');
     context = ol.dom.createCanvasContext2D(canvasWidth, canvasHeight);
     this.canvas_ = context.canvas;
     this.canvasSize_ = [canvasWidth, canvasHeight];
@@ -228,8 +232,10 @@ ol.renderer.canvas.TileLayer.prototype.prepareFrame =
     this.canvasTooBig_ =
         !ol.renderer.canvas.Layer.testCanvasSize(this.canvasSize_);
   } else {
-    goog.asserts.assert(!goog.isNull(this.canvasSize_));
-    goog.asserts.assert(!goog.isNull(this.context_));
+    goog.asserts.assert(!goog.isNull(this.canvasSize_),
+        'non-null canvasSize (because canvas is not null)');
+    goog.asserts.assert(!goog.isNull(this.context_),
+        'non-null context (because canvas is not null)');
     canvas = this.canvas_;
     context = this.context_;
     if (this.canvasSize_[0] < canvasWidth ||
@@ -277,7 +283,8 @@ ol.renderer.canvas.TileLayer.prototype.prepareFrame =
     canvasTileRangeWidth = canvasTileRange.getWidth();
   }
 
-  goog.asserts.assert(canvasTileRange.containsTileRange(tileRange));
+  goog.asserts.assert(canvasTileRange.containsTileRange(tileRange),
+      'tileRange is contained in canvasTileRange');
 
   /**
    * @type {Object.<number, Object.<string, ol.Tile>>}
diff --git a/src/ol/renderer/canvas/canvasvectorlayerrenderer.js b/src/ol/renderer/canvas/canvasvectorlayerrenderer.js
index 2ccec425c3..a4d72d9047 100644
--- a/src/ol/renderer/canvas/canvasvectorlayerrenderer.js
+++ b/src/ol/renderer/canvas/canvasvectorlayerrenderer.js
@@ -132,7 +132,7 @@ ol.renderer.canvas.VectorLayer.prototype.forEachFeatureAtCoordinate =
          * @return {?} Callback result.
          */
         function(feature) {
-          goog.asserts.assert(goog.isDef(feature));
+          goog.asserts.assert(goog.isDef(feature), 'received a feature');
           var key = goog.getUid(feature).toString();
           if (!(key in features)) {
             features[key] = true;
@@ -161,7 +161,8 @@ ol.renderer.canvas.VectorLayer.prototype.prepareFrame =
     function(frameState, layerState) {
 
   var vectorLayer = /** @type {ol.layer.Vector} */ (this.getLayer());
-  goog.asserts.assertInstanceof(vectorLayer, ol.layer.Vector);
+  goog.asserts.assertInstanceof(vectorLayer, ol.layer.Vector,
+      'layer is an instance of ol.layer.Vector');
   var vectorSource = vectorLayer.getSource();
 
   this.updateAttributions(
diff --git a/src/ol/renderer/dom/domimagelayerrenderer.js b/src/ol/renderer/dom/domimagelayerrenderer.js
index 6746de6691..67d4965b99 100644
--- a/src/ol/renderer/dom/domimagelayerrenderer.js
+++ b/src/ol/renderer/dom/domimagelayerrenderer.js
@@ -87,7 +87,8 @@ ol.renderer.dom.ImageLayer.prototype.prepareFrame =
 
   var image = this.image_;
   var imageLayer = this.getLayer();
-  goog.asserts.assertInstanceof(imageLayer, ol.layer.Image);
+  goog.asserts.assertInstanceof(imageLayer, ol.layer.Image,
+      'layer is an instance of ol.layer.Image');
   var imageSource = imageLayer.getSource();
 
   var hints = frameState.viewHints;
@@ -103,7 +104,8 @@ ol.renderer.dom.ImageLayer.prototype.prepareFrame =
     var projection = viewState.projection;
     var sourceProjection = imageSource.getProjection();
     if (!goog.isNull(sourceProjection)) {
-      goog.asserts.assert(ol.proj.equivalent(projection, sourceProjection));
+      goog.asserts.assert(ol.proj.equivalent(projection, sourceProjection),
+          'projection and sourceProjection are equivalent');
       projection = sourceProjection;
     }
     var image_ = imageSource.getImage(renderedExtent, viewResolution,
diff --git a/src/ol/renderer/dom/dommaprenderer.js b/src/ol/renderer/dom/dommaprenderer.js
index 4b966df86a..01e296c1a0 100644
--- a/src/ol/renderer/dom/dommaprenderer.js
+++ b/src/ol/renderer/dom/dommaprenderer.js
@@ -119,7 +119,7 @@ ol.renderer.dom.Map.prototype.createLayerRenderer = function(layer) {
       ol.ENABLE_VECTOR && layer instanceof ol.layer.Vector) {
     layerRenderer = new ol.renderer.dom.VectorLayer(layer);
   } else {
-    goog.asserts.fail();
+    goog.asserts.fail('unexpected layer configuration');
     return null;
   }
   return layerRenderer;
@@ -238,7 +238,8 @@ ol.renderer.dom.Map.prototype.renderFrame = function(frameState) {
     layer = layerState.layer;
     layerRenderer = /** @type {ol.renderer.dom.Layer} */ (
         this.getLayerRenderer(layer));
-    goog.asserts.assertInstanceof(layerRenderer, ol.renderer.dom.Layer);
+    goog.asserts.assertInstanceof(layerRenderer, ol.renderer.dom.Layer,
+        'renderer is an instance of ol.renderer.dom.Layer');
     addChild.call(this, layerRenderer.getTarget(), i);
     if (layerState.sourceState == ol.source.State.READY) {
       if (layerRenderer.prepareFrame(frameState, layerState)) {
@@ -254,7 +255,8 @@ ol.renderer.dom.Map.prototype.renderFrame = function(frameState) {
   for (layerKey in this.getLayerRenderers()) {
     if (!(layerKey in layerStates)) {
       layerRenderer = this.getLayerRendererByKey(layerKey);
-      goog.asserts.assertInstanceof(layerRenderer, ol.renderer.dom.Layer);
+      goog.asserts.assertInstanceof(layerRenderer, ol.renderer.dom.Layer,
+          'renderer is an instance of ol.renderer.dom.Layer');
       goog.dom.removeNode(layerRenderer.getTarget());
     }
   }
diff --git a/src/ol/renderer/dom/domtilelayerrenderer.js b/src/ol/renderer/dom/domtilelayerrenderer.js
index 091de7701d..1a58594f7e 100644
--- a/src/ol/renderer/dom/domtilelayerrenderer.js
+++ b/src/ol/renderer/dom/domtilelayerrenderer.js
@@ -101,7 +101,8 @@ ol.renderer.dom.TileLayer.prototype.prepareFrame =
   var projection = viewState.projection;
 
   var tileLayer = this.getLayer();
-  goog.asserts.assertInstanceof(tileLayer, ol.layer.Tile);
+  goog.asserts.assertInstanceof(tileLayer, ol.layer.Tile,
+      'layer is an instance of ol.layer.Tile');
   var tileSource = tileLayer.getSource();
   var tileGrid = tileSource.getTileGridForProjection(projection);
   var tileGutter = tileSource.getGutter();
@@ -353,7 +354,8 @@ ol.renderer.dom.TileLayerZ_.prototype.addTile = function(tile, tileGutter) {
   var tileCoordZ = tileCoord[0];
   var tileCoordX = tileCoord[1];
   var tileCoordY = tileCoord[2];
-  goog.asserts.assert(tileCoordZ == this.tileCoordOrigin_[0]);
+  goog.asserts.assert(tileCoordZ == this.tileCoordOrigin_[0],
+      'tileCoordZ matches z of tileCoordOrigin');
   var tileCoordKey = ol.tilecoord.toString(tileCoord);
   if (tileCoordKey in this.tiles_) {
     return;
diff --git a/src/ol/renderer/dom/domvectorlayerrenderer.js b/src/ol/renderer/dom/domvectorlayerrenderer.js
index 08aa7af139..a2c55c5057 100644
--- a/src/ol/renderer/dom/domvectorlayerrenderer.js
+++ b/src/ol/renderer/dom/domvectorlayerrenderer.js
@@ -99,7 +99,8 @@ ol.renderer.dom.VectorLayer.prototype.composeFrame =
     function(frameState, layerState) {
 
   var vectorLayer = /** @type {ol.layer.Vector} */ (this.getLayer());
-  goog.asserts.assertInstanceof(vectorLayer, ol.layer.Vector);
+  goog.asserts.assertInstanceof(vectorLayer, ol.layer.Vector,
+      'layer is an instance of ol.layer.Vector');
 
   var viewState = frameState.viewState;
   var viewCenter = viewState.center;
@@ -192,7 +193,7 @@ ol.renderer.dom.VectorLayer.prototype.forEachFeatureAtCoordinate =
          * @return {?} Callback result.
          */
         function(feature) {
-          goog.asserts.assert(goog.isDef(feature));
+          goog.asserts.assert(goog.isDef(feature), 'received a feature');
           var key = goog.getUid(feature).toString();
           if (!(key in features)) {
             features[key] = true;
@@ -221,7 +222,8 @@ ol.renderer.dom.VectorLayer.prototype.prepareFrame =
     function(frameState, layerState) {
 
   var vectorLayer = /** @type {ol.layer.Vector} */ (this.getLayer());
-  goog.asserts.assertInstanceof(vectorLayer, ol.layer.Vector);
+  goog.asserts.assertInstanceof(vectorLayer, ol.layer.Vector,
+      'layer is an instance of ol.layer.Vector');
   var vectorSource = vectorLayer.getSource();
 
   this.updateAttributions(
diff --git a/src/ol/renderer/layerrenderer.js b/src/ol/renderer/layerrenderer.js
index 44cc8af095..f1557c9f2e 100644
--- a/src/ol/renderer/layerrenderer.js
+++ b/src/ol/renderer/layerrenderer.js
@@ -149,14 +149,16 @@ ol.renderer.Layer.prototype.loadImage = function(image) {
     // the image is either "idle" or "loading", register the change
     // listener (a noop if the listener was already registered)
     goog.asserts.assert(imageState == ol.ImageState.IDLE ||
-        imageState == ol.ImageState.LOADING);
+        imageState == ol.ImageState.LOADING,
+        'imageState is "idle" or "loading"');
     goog.events.listen(image, goog.events.EventType.CHANGE,
         this.handleImageChange_, false, this);
   }
   if (imageState == ol.ImageState.IDLE) {
     image.load();
     imageState = image.getState();
-    goog.asserts.assert(imageState == ol.ImageState.LOADING);
+    goog.asserts.assert(imageState == ol.ImageState.LOADING,
+        'imageState is "loading"');
   }
   return imageState == ol.ImageState.LOADED;
 };
@@ -225,8 +227,8 @@ ol.renderer.Layer.prototype.updateLogos = function(frameState, source) {
     if (goog.isString(logo)) {
       frameState.logos[logo] = '';
     } else if (goog.isObject(logo)) {
-      goog.asserts.assertString(logo.href);
-      goog.asserts.assertString(logo.src);
+      goog.asserts.assertString(logo.href, 'logo.href is a string');
+      goog.asserts.assertString(logo.src, 'logo.src is a string');
       frameState.logos[logo.src] = logo.href;
     }
   }
diff --git a/src/ol/renderer/maprenderer.js b/src/ol/renderer/maprenderer.js
index c1c7748e67..64e32edc75 100644
--- a/src/ol/renderer/maprenderer.js
+++ b/src/ol/renderer/maprenderer.js
@@ -75,7 +75,8 @@ goog.inherits(ol.renderer.Map, goog.Disposable);
 ol.renderer.Map.prototype.calculateMatrices2D = function(frameState) {
   var viewState = frameState.viewState;
   var coordinateToPixelMatrix = frameState.coordinateToPixelMatrix;
-  goog.asserts.assert(!goog.isNull(coordinateToPixelMatrix));
+  goog.asserts.assert(!goog.isNull(coordinateToPixelMatrix),
+      'frameState has non-null coordinateToPixelMatrix');
   ol.vec.Mat4.makeTransform2D(coordinateToPixelMatrix,
       frameState.size[0] / 2, frameState.size[1] / 2,
       1 / viewState.resolution, -1 / viewState.resolution,
@@ -83,7 +84,7 @@ ol.renderer.Map.prototype.calculateMatrices2D = function(frameState) {
       -viewState.center[0], -viewState.center[1]);
   var inverted = goog.vec.Mat4.invert(
       coordinateToPixelMatrix, frameState.pixelToCoordinateMatrix);
-  goog.asserts.assert(inverted);
+  goog.asserts.assert(inverted, 'matrix could be inverted');
 };
 
 
@@ -145,7 +146,7 @@ ol.renderer.Map.prototype.forEachFeatureAtCoordinate =
          * @return {?} Callback result.
          */
         function(feature) {
-          goog.asserts.assert(goog.isDef(feature));
+          goog.asserts.assert(goog.isDef(feature), 'received a feature');
           var key = goog.getUid(feature).toString();
           if (!(key in features)) {
             features[key] = true;
@@ -277,7 +278,8 @@ ol.renderer.Map.prototype.getLayerRenderer = function(layer) {
  * @return {ol.renderer.Layer} Layer renderer.
  */
 ol.renderer.Map.prototype.getLayerRendererByKey = function(layerKey) {
-  goog.asserts.assert(layerKey in this.layerRenderers_);
+  goog.asserts.assert(layerKey in this.layerRenderers_,
+      'given layerKey (%s) exists in layerRenderers', layerKey);
   return this.layerRenderers_[layerKey];
 };
 
@@ -320,11 +322,13 @@ ol.renderer.Map.prototype.handleLayerRendererChange_ = function() {
  * @private
  */
 ol.renderer.Map.prototype.removeLayerRendererByKey_ = function(layerKey) {
-  goog.asserts.assert(layerKey in this.layerRenderers_);
+  goog.asserts.assert(layerKey in this.layerRenderers_,
+      'given layerKey (%s) exists in layerRenderers', layerKey);
   var layerRenderer = this.layerRenderers_[layerKey];
   delete this.layerRenderers_[layerKey];
 
-  goog.asserts.assert(layerKey in this.layerRendererListeners_);
+  goog.asserts.assert(layerKey in this.layerRendererListeners_,
+      'given layerKey (%s) exists in layerRendererListeners', layerKey);
   goog.events.unlistenByKey(this.layerRendererListeners_[layerKey]);
   delete this.layerRendererListeners_[layerKey];
 
diff --git a/src/ol/renderer/webgl/webglimagelayerrenderer.js b/src/ol/renderer/webgl/webglimagelayerrenderer.js
index 51f8394b23..e5a0b54750 100644
--- a/src/ol/renderer/webgl/webglimagelayerrenderer.js
+++ b/src/ol/renderer/webgl/webglimagelayerrenderer.js
@@ -110,7 +110,8 @@ ol.renderer.webgl.ImageLayer.prototype.prepareFrame =
   var image = this.image_;
   var texture = this.texture;
   var imageLayer = this.getLayer();
-  goog.asserts.assertInstanceof(imageLayer, ol.layer.Image);
+  goog.asserts.assertInstanceof(imageLayer, ol.layer.Image,
+      'layer is an instance of ol.layer.Image');
   var imageSource = imageLayer.getSource();
 
   var hints = frameState.viewHints;
@@ -125,7 +126,8 @@ ol.renderer.webgl.ImageLayer.prototype.prepareFrame =
     var projection = viewState.projection;
     var sourceProjection = imageSource.getProjection();
     if (!goog.isNull(sourceProjection)) {
-      goog.asserts.assert(ol.proj.equivalent(projection, sourceProjection));
+      goog.asserts.assert(ol.proj.equivalent(projection, sourceProjection),
+          'projection and sourceProjection are equivalent');
       projection = sourceProjection;
     }
     var image_ = imageSource.getImage(renderedExtent, viewResolution,
@@ -153,7 +155,7 @@ ol.renderer.webgl.ImageLayer.prototype.prepareFrame =
   }
 
   if (!goog.isNull(image)) {
-    goog.asserts.assert(!goog.isNull(texture));
+    goog.asserts.assert(!goog.isNull(texture), 'texture is not null');
 
     var canvas = this.mapRenderer.getContext().getCanvas();
 
diff --git a/src/ol/renderer/webgl/webglmaprenderer.js b/src/ol/renderer/webgl/webglmaprenderer.js
index 7fd95f3580..730c1863e9 100644
--- a/src/ol/renderer/webgl/webglmaprenderer.js
+++ b/src/ol/renderer/webgl/webglmaprenderer.js
@@ -96,7 +96,7 @@ ol.renderer.webgl.Map = function(container, map) {
     preserveDrawingBuffer: false,
     stencil: true
   });
-  goog.asserts.assert(!goog.isNull(this.gl_));
+  goog.asserts.assert(!goog.isNull(this.gl_), 'got a WebGLRenderingContext');
 
   /**
    * @private
@@ -190,7 +190,8 @@ ol.renderer.webgl.Map.prototype.bindTileTexture =
   var tileKey = tile.getKey();
   if (this.textureCache_.containsKey(tileKey)) {
     var textureCacheEntry = this.textureCache_.get(tileKey);
-    goog.asserts.assert(!goog.isNull(textureCacheEntry));
+    goog.asserts.assert(!goog.isNull(textureCacheEntry),
+        'a texture cache entry exists for key %s', tileKey);
     gl.bindTexture(goog.webgl.TEXTURE_2D, textureCacheEntry.texture);
     if (textureCacheEntry.magFilter != magFilter) {
       gl.texParameteri(
@@ -253,7 +254,7 @@ ol.renderer.webgl.Map.prototype.createLayerRenderer = function(layer) {
   } else if (ol.ENABLE_VECTOR && layer instanceof ol.layer.Vector) {
     return new ol.renderer.webgl.VectorLayer(this, layer);
   } else {
-    goog.asserts.fail();
+    goog.asserts.fail('unexpected layer configuration');
     return null;
   }
 };
@@ -397,7 +398,8 @@ ol.renderer.webgl.Map.prototype.handleWebGLContextLost = function(event) {
        * @param {Object.<string, ol.renderer.Layer>} object Object.
        */
       function(layerRenderer, key, object) {
-        goog.asserts.assertInstanceof(layerRenderer, ol.renderer.webgl.Layer);
+        goog.asserts.assertInstanceof(layerRenderer, ol.renderer.webgl.Layer,
+            'renderer is an instance of ol.renderer.webgl.Layer');
         var webGLLayerRenderer = /** @type {ol.renderer.webgl.Layer} */
             (layerRenderer);
         webGLLayerRenderer.handleWebGLContextLost();
@@ -482,7 +484,8 @@ ol.renderer.webgl.Map.prototype.renderFrame = function(frameState) {
     if (ol.layer.Layer.visibleAtResolution(layerState, viewResolution) &&
         layerState.sourceState == ol.source.State.READY) {
       layerRenderer = this.getLayerRenderer(layerState.layer);
-      goog.asserts.assertInstanceof(layerRenderer, ol.renderer.webgl.Layer);
+      goog.asserts.assertInstanceof(layerRenderer, ol.renderer.webgl.Layer,
+          'renderer is an instance of ol.renderer.webgl.Layer');
       if (layerRenderer.prepareFrame(frameState, layerState, context)) {
         layerStatesToDraw.push(layerState);
       }
@@ -508,7 +511,8 @@ ol.renderer.webgl.Map.prototype.renderFrame = function(frameState) {
   for (i = 0, ii = layerStatesToDraw.length; i < ii; ++i) {
     layerState = layerStatesToDraw[i];
     layerRenderer = this.getLayerRenderer(layerState.layer);
-    goog.asserts.assertInstanceof(layerRenderer, ol.renderer.webgl.Layer);
+    goog.asserts.assertInstanceof(layerRenderer, ol.renderer.webgl.Layer,
+        'renderer is an instance of ol.renderer.webgl.Layer');
     layerRenderer.composeFrame(frameState, layerState, context);
   }
 
@@ -569,7 +573,7 @@ ol.renderer.webgl.Map.prototype.forEachFeatureAtCoordinate =
          * @return {?} Callback result.
          */
         function(feature) {
-          goog.asserts.assert(goog.isDef(feature));
+          goog.asserts.assert(goog.isDef(feature), 'received a feature');
           var key = goog.getUid(feature).toString();
           if (!(key in features)) {
             features[key] = true;
diff --git a/src/ol/renderer/webgl/webgltilelayerrenderer.js b/src/ol/renderer/webgl/webgltilelayerrenderer.js
index 311608ff1a..43f623d286 100644
--- a/src/ol/renderer/webgl/webgltilelayerrenderer.js
+++ b/src/ol/renderer/webgl/webgltilelayerrenderer.js
@@ -151,7 +151,8 @@ ol.renderer.webgl.TileLayer.prototype.prepareFrame =
   var projection = viewState.projection;
 
   var tileLayer = this.getLayer();
-  goog.asserts.assertInstanceof(tileLayer, ol.layer.Tile);
+  goog.asserts.assertInstanceof(tileLayer, ol.layer.Tile,
+      'layer is an instance of ol.layer.Tile');
   var tileSource = tileLayer.getSource();
   var tileGrid = tileSource.getTileGridForProjection(projection);
   var z = tileGrid.getZForResolution(viewState.resolution);
diff --git a/src/ol/renderer/webgl/webglvectorlayerrenderer.js b/src/ol/renderer/webgl/webglvectorlayerrenderer.js
index 4a39054f34..cfbbaff09f 100644
--- a/src/ol/renderer/webgl/webglvectorlayerrenderer.js
+++ b/src/ol/renderer/webgl/webglvectorlayerrenderer.js
@@ -127,7 +127,7 @@ ol.renderer.webgl.VectorLayer.prototype.forEachFeatureAtCoordinate =
          * @return {?} Callback result.
          */
         function(feature) {
-          goog.asserts.assert(goog.isDef(feature));
+          goog.asserts.assert(goog.isDef(feature), 'received a feature');
           var key = goog.getUid(feature).toString();
           if (!(key in features)) {
             features[key] = true;
@@ -194,7 +194,8 @@ ol.renderer.webgl.VectorLayer.prototype.prepareFrame =
     function(frameState, layerState, context) {
 
   var vectorLayer = /** @type {ol.layer.Vector} */ (this.getLayer());
-  goog.asserts.assertInstanceof(vectorLayer, ol.layer.Vector);
+  goog.asserts.assertInstanceof(vectorLayer, ol.layer.Vector,
+      'layer is an instance of ol.layer.Vector');
   var vectorSource = vectorLayer.getSource();
 
   this.updateAttributions(
diff --git a/src/ol/source/bingmapssource.js b/src/ol/source/bingmapssource.js
index 7dd58cd724..cf72fce7dd 100644
--- a/src/ol/source/bingmapssource.js
+++ b/src/ol/source/bingmapssource.js
@@ -98,7 +98,8 @@ ol.source.BingMaps.prototype.handleImageryMetadataResponse =
   }
   //var copyright = response.copyright;  // FIXME do we need to display this?
   var resource = response.resourceSets[0].resources[0];
-  goog.asserts.assert(resource.imageWidth == resource.imageHeight);
+  goog.asserts.assert(resource.imageWidth == resource.imageHeight,
+      'resource has imageWidth equal to imageHeight, i.e. is square');
   var maxZoom = this.maxZoom_ == -1 ? resource.zoomMax : this.maxZoom_;
 
   var sourceProjection = this.getProjection();
@@ -129,7 +130,8 @@ ol.source.BingMaps.prototype.handleImageryMetadataResponse =
                      */
                     function(tileCoord, pixelRatio, projection) {
                       goog.asserts.assert(ol.proj.equivalent(
-                          projection, sourceProjection));
+                          projection, sourceProjection),
+                          'projections are equivalent');
                       if (goog.isNull(tileCoord)) {
                         return undefined;
                       } else {
diff --git a/src/ol/source/clustersource.js b/src/ol/source/clustersource.js
index 92a41e0581..18b07716ad 100644
--- a/src/ol/source/clustersource.js
+++ b/src/ol/source/clustersource.js
@@ -117,13 +117,14 @@ ol.source.Cluster.prototype.cluster_ = function() {
     var feature = features[i];
     if (!goog.object.containsKey(clustered, goog.getUid(feature).toString())) {
       var geometry = feature.getGeometry();
-      goog.asserts.assert(geometry instanceof ol.geom.Point);
+      goog.asserts.assert(geometry instanceof ol.geom.Point,
+          'feature geometry is a ol.geom.Point instance');
       var coordinates = geometry.getCoordinates();
       ol.extent.createOrUpdateFromCoordinate(coordinates, extent);
       ol.extent.buffer(extent, mapDistance, extent);
 
       var neighbors = this.source_.getFeaturesInExtent(extent);
-      goog.asserts.assert(neighbors.length >= 1);
+      goog.asserts.assert(neighbors.length >= 1, 'at least one neighbor found');
       neighbors = goog.array.filter(neighbors, function(neighbor) {
         var uid = goog.getUid(neighbor).toString();
         if (!goog.object.containsKey(clustered, uid)) {
@@ -137,7 +138,8 @@ ol.source.Cluster.prototype.cluster_ = function() {
     }
   }
   goog.asserts.assert(
-      goog.object.getCount(clustered) == this.source_.getFeatures().length);
+      goog.object.getCount(clustered) == this.source_.getFeatures().length,
+      'number of clustered equals number of features in the source');
 };
 
 
@@ -151,7 +153,8 @@ ol.source.Cluster.prototype.createCluster_ = function(features) {
   var centroid = [0, 0];
   for (var i = 0; i < length; i++) {
     var geometry = features[i].getGeometry();
-    goog.asserts.assert(geometry instanceof ol.geom.Point);
+    goog.asserts.assert(geometry instanceof ol.geom.Point,
+        'feature geometry is a ol.geom.Point instance');
     var coordinates = geometry.getCoordinates();
     ol.coordinate.add(centroid, coordinates);
   }
diff --git a/src/ol/source/formatvectorsource.js b/src/ol/source/formatvectorsource.js
index 7c94bf5fa2..8e3fd638d8 100644
--- a/src/ol/source/formatvectorsource.js
+++ b/src/ol/source/formatvectorsource.js
@@ -75,7 +75,8 @@ ol.source.FormatVector.prototype.loadFeaturesFromURL =
        */
       function(event) {
         var xhrIo = event.target;
-        goog.asserts.assertInstanceof(xhrIo, goog.net.XhrIo);
+        goog.asserts.assertInstanceof(xhrIo, goog.net.XhrIo,
+            'event.target/xhrIo is an instance of goog.net.XhrIo');
         if (xhrIo.isSuccess()) {
           var type = this.format.getType();
           /** @type {ArrayBuffer|Document|Node|Object|string|undefined} */
@@ -83,7 +84,8 @@ ol.source.FormatVector.prototype.loadFeaturesFromURL =
           if (type == ol.format.FormatType.BINARY &&
               ol.has.ARRAY_BUFFER) {
             source = xhrIo.getResponse();
-            goog.asserts.assertInstanceof(source, ArrayBuffer);
+            goog.asserts.assertInstanceof(source, ArrayBuffer,
+                'source is an instance of ArrayBuffer');
           } else if (type == ol.format.FormatType.JSON) {
             source = xhrIo.getResponseText();
           } else if (type == ol.format.FormatType.TEXT) {
@@ -96,13 +98,13 @@ ol.source.FormatVector.prototype.loadFeaturesFromURL =
               source = ol.xml.parse(xhrIo.getResponseText());
             }
           } else {
-            goog.asserts.fail();
+            goog.asserts.fail('unexpected format type');
           }
           if (goog.isDefAndNotNull(source)) {
             success.call(thisArg, this.readFeatures(source));
           } else {
             this.setState(ol.source.State.ERROR);
-            goog.asserts.fail();
+            goog.asserts.fail('undefined or null source');
           }
         } else {
           error.call(thisArg);
diff --git a/src/ol/source/imagesource.js b/src/ol/source/imagesource.js
index d5e650e255..63b4a2532d 100644
--- a/src/ol/source/imagesource.js
+++ b/src/ol/source/imagesource.js
@@ -53,7 +53,7 @@ ol.source.Image = function(options) {
       goog.array.isSorted(this.resolutions_,
           function(a, b) {
             return b - a;
-          }, true));
+          }, true), 'resolutions must be null or sorted in descending order');
 
 };
 goog.inherits(ol.source.Image, ol.source.Source);
diff --git a/src/ol/source/imagevectorsource.js b/src/ol/source/imagevectorsource.js
index 67923a7b85..6cf21900fa 100644
--- a/src/ol/source/imagevectorsource.js
+++ b/src/ol/source/imagevectorsource.js
@@ -166,7 +166,7 @@ ol.source.ImageVector.prototype.forEachFeatureAtCoordinate = function(
          * @return {?} Callback result.
          */
         function(feature) {
-          goog.asserts.assert(goog.isDef(feature));
+          goog.asserts.assert(goog.isDef(feature), 'passed a feature');
           var key = goog.getUid(feature).toString();
           if (!(key in features)) {
             features[key] = true;
diff --git a/src/ol/source/imagewmssource.js b/src/ol/source/imagewmssource.js
index 9f1f544e2a..2feb19c532 100644
--- a/src/ol/source/imagewmssource.js
+++ b/src/ol/source/imagewmssource.js
@@ -139,7 +139,8 @@ ol.source.ImageWMS.GETFEATUREINFO_IMAGE_SIZE_ = [101, 101];
 ol.source.ImageWMS.prototype.getGetFeatureInfoUrl =
     function(coordinate, resolution, projection, params) {
 
-  goog.asserts.assert(!('VERSION' in params));
+  goog.asserts.assert(!('VERSION' in params),
+      'key VERSION is not allowed in params');
 
   if (!goog.isDef(this.url_)) {
     return undefined;
@@ -279,7 +280,7 @@ ol.source.ImageWMS.prototype.getImageLoadFunction = function() {
 ol.source.ImageWMS.prototype.getRequestUrl_ =
     function(extent, size, pixelRatio, projection, params) {
 
-  goog.asserts.assert(goog.isDef(this.url_));
+  goog.asserts.assert(goog.isDef(this.url_), 'url is defined');
 
   params[this.v13_ ? 'CRS' : 'SRS'] = projection.getCode();
 
@@ -303,7 +304,7 @@ ol.source.ImageWMS.prototype.getRequestUrl_ =
         params['DPI'] = 90 * pixelRatio;
         break;
       default:
-        goog.asserts.fail();
+        goog.asserts.fail('unknown serverType configured');
         break;
     }
   }
diff --git a/src/ol/source/mapquestsource.js b/src/ol/source/mapquestsource.js
index b0f7f05fe5..df021a5575 100644
--- a/src/ol/source/mapquestsource.js
+++ b/src/ol/source/mapquestsource.js
@@ -20,7 +20,8 @@ goog.require('ol.source.XYZ');
 ol.source.MapQuest = function(opt_options) {
 
   var options = goog.isDef(opt_options) ? opt_options : {};
-  goog.asserts.assert(options.layer in ol.source.MapQuestConfig);
+  goog.asserts.assert(options.layer in ol.source.MapQuestConfig,
+      'known layer configured');
 
   var layerConfig = ol.source.MapQuestConfig[options.layer];
 
diff --git a/src/ol/source/stamensource.js b/src/ol/source/stamensource.js
index 2980756c2b..2805a5fccd 100644
--- a/src/ol/source/stamensource.js
+++ b/src/ol/source/stamensource.js
@@ -91,10 +91,12 @@ ol.source.Stamen = function(options) {
 
   var i = options.layer.indexOf('-');
   var provider = i == -1 ? options.layer : options.layer.slice(0, i);
-  goog.asserts.assert(provider in ol.source.StamenProviderConfig);
+  goog.asserts.assert(provider in ol.source.StamenProviderConfig,
+      'known provider configured');
   var providerConfig = ol.source.StamenProviderConfig[provider];
 
-  goog.asserts.assert(options.layer in ol.source.StamenLayerConfig);
+  goog.asserts.assert(options.layer in ol.source.StamenLayerConfig,
+      'known layer configured');
   var layerConfig = ol.source.StamenLayerConfig[options.layer];
 
   var root = ol.IS_HTTPS ? 'https://stamen-tiles-{a-d}.a.ssl.fastly.net/' :
diff --git a/src/ol/source/tileimagesource.js b/src/ol/source/tileimagesource.js
index dc453c6eb1..a70e479135 100644
--- a/src/ol/source/tileimagesource.js
+++ b/src/ol/source/tileimagesource.js
@@ -90,7 +90,7 @@ ol.source.TileImage.prototype.getTile =
   if (this.tileCache.containsKey(tileCoordKey)) {
     return /** @type {!ol.Tile} */ (this.tileCache.get(tileCoordKey));
   } else {
-    goog.asserts.assert(projection);
+    goog.asserts.assert(projection, 'argument projection is truthy');
     var tileCoord = [z, x, y];
     var urlTileCoord = this.getWrapXTileCoord(tileCoord, projection);
     var tileUrl = goog.isNull(urlTileCoord) ? undefined :
diff --git a/src/ol/source/tilejsonsource.js b/src/ol/source/tilejsonsource.js
index 0cfc7e2df5..609ce6267f 100644
--- a/src/ol/source/tilejsonsource.js
+++ b/src/ol/source/tilejsonsource.js
@@ -65,7 +65,7 @@ ol.source.TileJSON.prototype.handleTileJSONResponse = function(tileJSON) {
   }
 
   if (goog.isDef(tileJSON.scheme)) {
-    goog.asserts.assert(tileJSON.scheme == 'xyz');
+    goog.asserts.assert(tileJSON.scheme == 'xyz', 'tileJSON-scheme is "xyz"');
   }
   var minZoom = tileJSON.minzoom || 0;
   var maxZoom = tileJSON.maxzoom || 22;
diff --git a/src/ol/source/tileutfgridsource.js b/src/ol/source/tileutfgridsource.js
index 7a476840f5..866137b4d4 100644
--- a/src/ol/source/tileutfgridsource.js
+++ b/src/ol/source/tileutfgridsource.js
@@ -117,7 +117,7 @@ ol.source.TileUTFGrid.prototype.handleTileJSONResponse = function(tileJSON) {
   }
 
   if (goog.isDef(tileJSON.scheme)) {
-    goog.asserts.assert(tileJSON.scheme == 'xyz');
+    goog.asserts.assert(tileJSON.scheme == 'xyz', 'tileJSON-scheme is "xyz"');
   }
   var minZoom = tileJSON.minzoom || 0;
   var maxZoom = tileJSON.maxzoom || 22;
@@ -175,7 +175,7 @@ ol.source.TileUTFGrid.prototype.getTile =
   if (this.tileCache.containsKey(tileCoordKey)) {
     return /** @type {!ol.Tile} */ (this.tileCache.get(tileCoordKey));
   } else {
-    goog.asserts.assert(projection);
+    goog.asserts.assert(projection, 'argument projection is truthy');
     var tileCoord = [z, x, y];
     var tileUrl = this.tileUrlFunction_(tileCoord, pixelRatio, projection);
     var tile = new ol.source.TileUTFGridTile_(
diff --git a/src/ol/source/tilevectorsource.js b/src/ol/source/tilevectorsource.js
index 84eea90faa..1a3642fb3e 100644
--- a/src/ol/source/tilevectorsource.js
+++ b/src/ol/source/tilevectorsource.js
@@ -121,7 +121,8 @@ ol.source.TileVector.prototype.forEachFeatureAtCoordinateAndResolution =
     for (i = 0, ii = features.length; i < ii; ++i) {
       var feature = features[i];
       var geometry = feature.getGeometry();
-      goog.asserts.assert(goog.isDefAndNotNull(geometry));
+      goog.asserts.assert(goog.isDefAndNotNull(geometry),
+          'feature geometry is defined and not null');
       if (geometry.containsCoordinate(coordinate)) {
         var result = callback.call(opt_this, feature);
         if (result) {
diff --git a/src/ol/source/tilewmssource.js b/src/ol/source/tilewmssource.js
index 82c067d687..aa41a1b5ff 100644
--- a/src/ol/source/tilewmssource.js
+++ b/src/ol/source/tilewmssource.js
@@ -129,7 +129,8 @@ goog.inherits(ol.source.TileWMS, ol.source.TileImage);
 ol.source.TileWMS.prototype.getGetFeatureInfoUrl =
     function(coordinate, resolution, projection, params) {
 
-  goog.asserts.assert(!('VERSION' in params));
+  goog.asserts.assert(!('VERSION' in params),
+      'key VERSION is not allowed in params');
 
   var projectionObj = ol.proj.get(projection);
 
@@ -248,7 +249,7 @@ ol.source.TileWMS.prototype.getRequestUrl_ =
         params['DPI'] = 90 * pixelRatio;
         break;
       default:
-        goog.asserts.fail();
+        goog.asserts.fail('unknown serverType configured');
         break;
     }
   }
diff --git a/src/ol/source/vectorsource.js b/src/ol/source/vectorsource.js
index ccfe2cbaa0..352c111b41 100644
--- a/src/ol/source/vectorsource.js
+++ b/src/ol/source/vectorsource.js
@@ -158,7 +158,8 @@ ol.source.Vector.prototype.addFeatureInternal = function(feature) {
  * @private
  */
 ol.source.Vector.prototype.setupChangeEvents_ = function(featureKey, feature) {
-  goog.asserts.assert(!(featureKey in this.featureChangeKeys_));
+  goog.asserts.assert(!(featureKey in this.featureChangeKeys_),
+      'key (%s) not yet registered in featurChangeKey', featureKey);
   this.featureChangeKeys_[featureKey] = [
     goog.events.listen(feature,
         goog.events.EventType.CHANGE,
@@ -251,9 +252,12 @@ ol.source.Vector.prototype.clear = function(opt_fast) {
     var rmFeatureInternal = this.removeFeatureInternal;
     this.rBush_.forEach(rmFeatureInternal, this);
     goog.object.forEach(this.nullGeometryFeatures_, rmFeatureInternal, this);
-    goog.asserts.assert(goog.object.isEmpty(this.featureChangeKeys_));
-    goog.asserts.assert(goog.object.isEmpty(this.idIndex_));
-    goog.asserts.assert(goog.object.isEmpty(this.undefIdIndex_));
+    goog.asserts.assert(goog.object.isEmpty(this.featureChangeKeys_),
+        'featureChangeKeys is an empty object now');
+    goog.asserts.assert(goog.object.isEmpty(this.idIndex_),
+        'idIndex is an empty object now');
+    goog.asserts.assert(goog.object.isEmpty(this.undefIdIndex_),
+        'undefIdIndex is an empty object now');
   }
 
   this.rBush_.clear();
@@ -300,7 +304,8 @@ ol.source.Vector.prototype.forEachFeatureAtCoordinateDirect =
   var extent = [coordinate[0], coordinate[1], coordinate[0], coordinate[1]];
   return this.forEachFeatureInExtent(extent, function(feature) {
     var geometry = feature.getGeometry();
-    goog.asserts.assert(goog.isDefAndNotNull(geometry));
+    goog.asserts.assert(goog.isDefAndNotNull(geometry),
+        'feature geometry is defined and not null');
     if (geometry.containsCoordinate(coordinate)) {
       return callback.call(opt_this, feature);
     } else {
@@ -375,7 +380,8 @@ ol.source.Vector.prototype.forEachFeatureIntersectingExtent =
        */
       function(feature) {
         var geometry = feature.getGeometry();
-        goog.asserts.assert(goog.isDefAndNotNull(geometry));
+        goog.asserts.assert(goog.isDefAndNotNull(geometry),
+            'feature geometry is defined and not null');
         if (geometry.intersectsExtent(extent)) {
           var result = callback.call(opt_this, feature);
           if (result) {
@@ -452,7 +458,8 @@ ol.source.Vector.prototype.getClosestFeatureToCoordinate =
        */
       function(feature) {
         var geometry = feature.getGeometry();
-        goog.asserts.assert(goog.isDefAndNotNull(geometry));
+        goog.asserts.assert(goog.isDefAndNotNull(geometry),
+            'feature geometry is defined and not null');
         var previousMinSquaredDistance = minSquaredDistance;
         minSquaredDistance = geometry.closestPointXY(
             x, y, closestPoint, minSquaredDistance);
@@ -542,7 +549,8 @@ ol.source.Vector.prototype.handleFeatureChange_ = function(event) {
           'Expected feature to be removed from index');
       this.undefIdIndex_[featureKey] = feature;
     } else {
-      goog.asserts.assert(this.undefIdIndex_[featureKey] === feature);
+      goog.asserts.assert(this.undefIdIndex_[featureKey] === feature,
+          'feature keyed under %s in undefIdKeys', featureKey);
     }
   }
   this.changed();
@@ -594,7 +602,8 @@ ol.source.Vector.prototype.removeFeature = function(feature) {
  */
 ol.source.Vector.prototype.removeFeatureInternal = function(feature) {
   var featureKey = goog.getUid(feature).toString();
-  goog.asserts.assert(featureKey in this.featureChangeKeys_);
+  goog.asserts.assert(featureKey in this.featureChangeKeys_,
+      'featureKey exists in featureChangeKeys');
   goog.array.forEach(this.featureChangeKeys_[featureKey],
       goog.events.unlistenByKey);
   delete this.featureChangeKeys_[featureKey];
diff --git a/src/ol/source/wmtssource.js b/src/ol/source/wmtssource.js
index 19fb88f5e5..f1bd00fc02 100644
--- a/src/ol/source/wmtssource.js
+++ b/src/ol/source/wmtssource.js
@@ -177,7 +177,8 @@ ol.source.WMTS = function(options) {
        * @return {ol.TileCoord} Tile coordinate.
        */
       function(tileCoord, projection, opt_tileCoord) {
-        goog.asserts.assert(!goog.isNull(tileGrid));
+        goog.asserts.assert(!goog.isNull(tileGrid),
+            'tileGrid must not be null');
         if (tileGrid.getResolutions().length <= tileCoord[0]) {
           return null;
         }
@@ -328,15 +329,18 @@ ol.source.WMTS.optionsFromCapabilities = function(wmtsCap, config) {
   /* jshint -W069 */
 
   // TODO: add support for TileMatrixLimits
-  goog.asserts.assert(!goog.isNull(config['layer']));
+  goog.asserts.assert(!goog.isNull(config['layer']),
+      'config "layer" must not be null');
 
   var layers = wmtsCap['Contents']['Layer'];
   var l = goog.array.find(layers, function(elt, index, array) {
     return elt['Identifier'] == config['layer'];
   });
-  goog.asserts.assert(!goog.isNull(l));
+  goog.asserts.assert(!goog.isNull(l),
+      'found a matching layer in Contents/Layer');
 
-  goog.asserts.assert(l['TileMatrixSetLink'].length > 0);
+  goog.asserts.assert(l['TileMatrixSetLink'].length > 0,
+      'layer has TileMatrixSetLink');
   var idx, matrixSet, wrapX;
   if (l['TileMatrixSetLink'].length > 1) {
     idx = goog.array.findIndex(l['TileMatrixSetLink'],
@@ -359,7 +363,8 @@ ol.source.WMTS.optionsFromCapabilities = function(wmtsCap, config) {
   matrixSet = /** @type {string} */
       (l['TileMatrixSetLink'][idx]['TileMatrixSet']);
 
-  goog.asserts.assert(!goog.isNull(matrixSet));
+  goog.asserts.assert(!goog.isNull(matrixSet),
+      'TileMatrixSet must not be null');
 
   var wgs84BoundingBox = l['WGS84BoundingBox'];
   if (goog.isDef(wgs84BoundingBox)) {
@@ -390,11 +395,12 @@ ol.source.WMTS.optionsFromCapabilities = function(wmtsCap, config) {
       var key = elt['Identifier'];
       var value = elt['default'];
       if (goog.isDef(value)) {
-        goog.asserts.assert(goog.array.contains(elt['values'], value));
+        goog.asserts.assert(goog.array.contains(elt['values'], value),
+            'default value contained in values');
       } else {
         value = elt['values'][0];
       }
-      goog.asserts.assert(goog.isDef(value));
+      goog.asserts.assert(goog.isDef(value), 'value could be found');
       dimensions[key] = value;
     });
   }
@@ -403,7 +409,8 @@ ol.source.WMTS.optionsFromCapabilities = function(wmtsCap, config) {
   var matrixSetObj = goog.array.find(matrixSets, function(elt, index, array) {
     return elt['Identifier'] == matrixSet;
   });
-  goog.asserts.assert(!goog.isNull(matrixSetObj));
+  goog.asserts.assert(!goog.isNull(matrixSetObj),
+      'found matrixSet in Contents/TileMatrixSet');
 
   var tileGrid = ol.tilegrid.WMTS.createFromCapabilitiesMatrixSet(
       matrixSetObj);
@@ -422,7 +429,9 @@ ol.source.WMTS.optionsFromCapabilities = function(wmtsCap, config) {
   requestEncoding = goog.isDef(requestEncoding) ? requestEncoding : '';
 
   goog.asserts.assert(
-      goog.array.contains(['REST', 'RESTful', 'KVP', ''], requestEncoding));
+      goog.array.contains(['REST', 'RESTful', 'KVP', ''], requestEncoding),
+      'requestEncoding (%s) is one of "REST", "RESTful", "KVP" or ""',
+      requestEncoding);
 
   if (!wmtsCap['OperationsMetadata'].hasOwnProperty('GetTile') ||
       goog.string.startsWith(requestEncoding, 'REST')) {
@@ -448,7 +457,7 @@ ol.source.WMTS.optionsFromCapabilities = function(wmtsCap, config) {
 
     }
   }
-  goog.asserts.assert(urls.length > 0);
+  goog.asserts.assert(urls.length > 0, 'At least one URL found');
 
   return {
     urls: urls,
diff --git a/src/ol/structs/lrucache.js b/src/ol/structs/lrucache.js
index d1b1f3a6c5..8aac72c41d 100644
--- a/src/ol/structs/lrucache.js
+++ b/src/ol/structs/lrucache.js
@@ -47,32 +47,42 @@ ol.structs.LRUCache = function() {
  */
 ol.structs.LRUCache.prototype.assertValid = function() {
   if (this.count_ === 0) {
-    goog.asserts.assert(goog.object.isEmpty(this.entries_));
-    goog.asserts.assert(goog.isNull(this.oldest_));
-    goog.asserts.assert(goog.isNull(this.newest_));
+    goog.asserts.assert(goog.object.isEmpty(this.entries_),
+        'entries must be an empty object (count = 0)');
+    goog.asserts.assert(goog.isNull(this.oldest_),
+        'oldest must be null (count = 0)');
+    goog.asserts.assert(goog.isNull(this.newest_),
+        'newest must be null (count = 0)');
   } else {
-    goog.asserts.assert(goog.object.getCount(this.entries_) == this.count_);
-    goog.asserts.assert(!goog.isNull(this.oldest_));
-    goog.asserts.assert(goog.isNull(this.oldest_.older));
-    goog.asserts.assert(!goog.isNull(this.newest_));
-    goog.asserts.assert(goog.isNull(this.newest_.newer));
+    goog.asserts.assert(goog.object.getCount(this.entries_) == this.count_,
+        'number of entries matches count');
+    goog.asserts.assert(!goog.isNull(this.oldest_),
+        'we have an oldest entry');
+    goog.asserts.assert(goog.isNull(this.oldest_.older),
+        'no entry is older than oldest');
+    goog.asserts.assert(!goog.isNull(this.newest_),
+        'we have a newest entry');
+    goog.asserts.assert(goog.isNull(this.newest_.newer),
+        'no entry is newer than newest');
     var i, entry;
     var older = null;
     i = 0;
     for (entry = this.oldest_; !goog.isNull(entry); entry = entry.newer) {
-      goog.asserts.assert(entry.older === older);
+      goog.asserts.assert(entry.older === older,
+          'entry.older links to correct older');
       older = entry;
       ++i;
     }
-    goog.asserts.assert(i == this.count_);
+    goog.asserts.assert(i == this.count_, 'iterated correct amount of times');
     var newer = null;
     i = 0;
     for (entry = this.newest_; !goog.isNull(entry); entry = entry.older) {
-      goog.asserts.assert(entry.newer === newer);
+      goog.asserts.assert(entry.newer === newer,
+          'entry.newer links to correct newer');
       newer = entry;
       ++i;
     }
-    goog.asserts.assert(i == this.count_);
+    goog.asserts.assert(i == this.count_, 'iterated correct amount of times');
   }
 };
 
@@ -120,7 +130,7 @@ ol.structs.LRUCache.prototype.forEach = function(f, opt_this) {
  */
 ol.structs.LRUCache.prototype.get = function(key) {
   var entry = this.entries_[key];
-  goog.asserts.assert(goog.isDef(entry));
+  goog.asserts.assert(goog.isDef(entry), 'an entry exists for key %s', key);
   if (entry === this.newest_) {
     return entry.value_;
   } else if (entry === this.oldest_) {
@@ -156,7 +166,7 @@ ol.structs.LRUCache.prototype.getKeys = function() {
   for (entry = this.newest_; !goog.isNull(entry); entry = entry.older) {
     keys[i++] = entry.key_;
   }
-  goog.asserts.assert(i == this.count_);
+  goog.asserts.assert(i == this.count_, 'iterated correct number of times');
   return keys;
 };
 
@@ -171,7 +181,7 @@ ol.structs.LRUCache.prototype.getValues = function() {
   for (entry = this.newest_; !goog.isNull(entry); entry = entry.older) {
     values[i++] = entry.value_;
   }
-  goog.asserts.assert(i == this.count_);
+  goog.asserts.assert(i == this.count_, 'iterated correct number of times');
   return values;
 };
 
@@ -180,7 +190,7 @@ ol.structs.LRUCache.prototype.getValues = function() {
  * @return {T} Last value.
  */
 ol.structs.LRUCache.prototype.peekLast = function() {
-  goog.asserts.assert(!goog.isNull(this.oldest_));
+  goog.asserts.assert(!goog.isNull(this.oldest_), 'oldest must not be null');
   return this.oldest_.value_;
 };
 
@@ -189,7 +199,7 @@ ol.structs.LRUCache.prototype.peekLast = function() {
  * @return {string} Last key.
  */
 ol.structs.LRUCache.prototype.peekLastKey = function() {
-  goog.asserts.assert(!goog.isNull(this.oldest_));
+  goog.asserts.assert(!goog.isNull(this.oldest_), 'oldest must not be null');
   return this.oldest_.key_;
 };
 
@@ -198,10 +208,11 @@ ol.structs.LRUCache.prototype.peekLastKey = function() {
  * @return {T} value Value.
  */
 ol.structs.LRUCache.prototype.pop = function() {
-  goog.asserts.assert(!goog.isNull(this.oldest_));
-  goog.asserts.assert(!goog.isNull(this.newest_));
+  goog.asserts.assert(!goog.isNull(this.oldest_), 'oldest must not be null');
+  goog.asserts.assert(!goog.isNull(this.newest_), 'newest must not be null');
   var entry = this.oldest_;
-  goog.asserts.assert(entry.key_ in this.entries_);
+  goog.asserts.assert(entry.key_ in this.entries_,
+      'oldest is indexed in entries');
   delete this.entries_[entry.key_];
   if (!goog.isNull(entry.newer)) {
     entry.newer.older = null;
@@ -220,8 +231,10 @@ ol.structs.LRUCache.prototype.pop = function() {
  * @param {T} value Value.
  */
 ol.structs.LRUCache.prototype.set = function(key, value) {
-  goog.asserts.assert(!(key in {}));
-  goog.asserts.assert(!(key in this.entries_));
+  goog.asserts.assert(!(key in {}),
+      'key is not a standard property of objects (e.g. "__proto__")');
+  goog.asserts.assert(!(key in this.entries_),
+      'key is not used already');
   var entry = {
     key_: key,
     newer: null,
diff --git a/src/ol/structs/priorityqueue.js b/src/ol/structs/priorityqueue.js
index 714c59dd64..e943796e34 100644
--- a/src/ol/structs/priorityqueue.js
+++ b/src/ol/structs/priorityqueue.js
@@ -63,7 +63,7 @@ ol.structs.PriorityQueue.DROP = Infinity;
 
 
 /**
- * FIXME empty desciption for jsdoc
+ * FIXME empty description for jsdoc
  */
 ol.structs.PriorityQueue.prototype.assertValid = function() {
   var elements = this.elements_;
@@ -73,8 +73,12 @@ ol.structs.PriorityQueue.prototype.assertValid = function() {
   var i, priority;
   for (i = 0; i < (n >> 1) - 1; ++i) {
     priority = priorities[i];
-    goog.asserts.assert(priority <= priorities[this.getLeftChildIndex_(i)]);
-    goog.asserts.assert(priority <= priorities[this.getRightChildIndex_(i)]);
+    goog.asserts.assert(priority <= priorities[this.getLeftChildIndex_(i)],
+        'priority smaller than or equal to priority of left child (%s <= %s)',
+        priority, priorities[this.getLeftChildIndex_(i)]);
+    goog.asserts.assert(priority <= priorities[this.getRightChildIndex_(i)],
+        'priority smaller than or equal to priority of right child (%s <= %s)',
+        priority, priorities[this.getRightChildIndex_(i)]);
   }
 };
 
@@ -95,7 +99,8 @@ ol.structs.PriorityQueue.prototype.clear = function() {
  */
 ol.structs.PriorityQueue.prototype.dequeue = function() {
   var elements = this.elements_;
-  goog.asserts.assert(elements.length > 0);
+  goog.asserts.assert(elements.length > 0,
+      'must have elements in order to be able to dequeue');
   var priorities = this.priorities_;
   var element = elements[0];
   if (elements.length == 1) {
@@ -107,7 +112,8 @@ ol.structs.PriorityQueue.prototype.dequeue = function() {
     this.siftUp_(0);
   }
   var elementKey = this.keyFunction_(element);
-  goog.asserts.assert(elementKey in this.queuedElements_);
+  goog.asserts.assert(elementKey in this.queuedElements_,
+      'key %s is not listed as queued', elementKey);
   delete this.queuedElements_[elementKey];
   return element;
 };
@@ -118,7 +124,8 @@ ol.structs.PriorityQueue.prototype.dequeue = function() {
  * @param {T} element Element.
  */
 ol.structs.PriorityQueue.prototype.enqueue = function(element) {
-  goog.asserts.assert(!(this.keyFunction_(element) in this.queuedElements_));
+  goog.asserts.assert(!(this.keyFunction_(element) in this.queuedElements_),
+      'key %s is already listed as queued', this.keyFunction_(element));
   var priority = this.priorityFunction_(element);
   if (priority != ol.structs.PriorityQueue.DROP) {
     this.elements_.push(element);
diff --git a/src/ol/structs/rbush.js b/src/ol/structs/rbush.js
index 7efa537782..81e0961cd9 100644
--- a/src/ol/structs/rbush.js
+++ b/src/ol/structs/rbush.js
@@ -61,7 +61,8 @@ ol.structs.RBush.prototype.insert = function(extent, value) {
   this.rbush_.insert(item);
   // remember the object that was added to the internal rbush
   goog.asserts.assert(
-      !goog.object.containsKey(this.items_, goog.getUid(value)));
+      !goog.object.containsKey(this.items_, goog.getUid(value)),
+      'uid (%s) of value (%s) already exists', goog.getUid(value), value);
   this.items_[goog.getUid(value)] = item;
 };
 
@@ -75,7 +76,9 @@ ol.structs.RBush.prototype.load = function(extents, values) {
   if (goog.DEBUG && this.readers_) {
     throw new Error('Can not insert values while reading');
   }
-  goog.asserts.assert(extents.length === values.length);
+  goog.asserts.assert(extents.length === values.length,
+      'extens and values must have same length (%s === %s)',
+      extents.length, values.length);
 
   var items = new Array(values.length);
   for (var i = 0, l = values.length; i < l; i++) {
@@ -91,7 +94,8 @@ ol.structs.RBush.prototype.load = function(extents, values) {
     ];
     items[i] = item;
     goog.asserts.assert(
-        !goog.object.containsKey(this.items_, goog.getUid(value)));
+        !goog.object.containsKey(this.items_, goog.getUid(value)),
+        'uid (%s) of value (%s) already exists', goog.getUid(value), value);
     this.items_[goog.getUid(value)] = item;
   }
   this.rbush_.load(items);
@@ -108,7 +112,8 @@ ol.structs.RBush.prototype.remove = function(value) {
     throw new Error('Can not remove value while reading');
   }
   var uid = goog.getUid(value);
-  goog.asserts.assert(goog.object.containsKey(this.items_, uid));
+  goog.asserts.assert(goog.object.containsKey(this.items_, uid),
+      'uid (%s) of value (%s) does not exist', uid, value);
 
   // get the object in which the value was wrapped when adding to the
   // internal rbush. then use that object to do the removal.
@@ -125,7 +130,8 @@ ol.structs.RBush.prototype.remove = function(value) {
  */
 ol.structs.RBush.prototype.update = function(extent, value) {
   var uid = goog.getUid(value);
-  goog.asserts.assert(goog.object.containsKey(this.items_, uid));
+  goog.asserts.assert(goog.object.containsKey(this.items_, uid),
+      'uid (%s) of value (%s) does not exist', uid, value);
 
   var item = this.items_[uid];
   if (!ol.extent.equals(item.slice(0, 4), extent)) {
diff --git a/src/ol/style/atlasmanager.js b/src/ol/style/atlasmanager.js
index 8daea3b279..f49a41cc67 100644
--- a/src/ol/style/atlasmanager.js
+++ b/src/ol/style/atlasmanager.js
@@ -102,7 +102,8 @@ ol.style.AtlasManager.prototype.getInfo = function(id) {
   }
   /** @type {?ol.style.AtlasInfo} */
   var hitInfo = this.getInfo_(this.hitAtlases_, id);
-  goog.asserts.assert(!goog.isNull(hitInfo));
+  goog.asserts.assert(!goog.isNull(hitInfo),
+      'hitInfo must not be null');
 
   return this.mergeInfos_(info, hitInfo);
 };
@@ -137,8 +138,10 @@ ol.style.AtlasManager.prototype.getInfo_ = function(atlases, id) {
  *    entry, or `null` if the entry is not part of the atlases.
  */
 ol.style.AtlasManager.prototype.mergeInfos_ = function(info, hitInfo) {
-  goog.asserts.assert(info.offsetX === hitInfo.offsetX);
-  goog.asserts.assert(info.offsetY === hitInfo.offsetY);
+  goog.asserts.assert(info.offsetX === hitInfo.offsetX,
+      'in order to merge, offsetX of info and hitInfo must be equal');
+  goog.asserts.assert(info.offsetY === hitInfo.offsetY,
+      'in order to merge, offsetY of info and hitInfo must be equal');
   return /** @type {ol.style.AtlasManagerInfo} */ ({
     offsetX: info.offsetX,
     offsetY: info.offsetY,
@@ -194,7 +197,8 @@ ol.style.AtlasManager.prototype.add =
   /** @type {?ol.style.AtlasInfo} */
   var hitInfo = this.add_(true,
       id, width, height, renderHitCallback, opt_this);
-  goog.asserts.assert(!goog.isNull(hitInfo));
+  goog.asserts.assert(!goog.isNull(hitInfo),
+      'hitInfo must not be null');
 
   return this.mergeInfos_(info, hitInfo);
 };
@@ -240,7 +244,7 @@ ol.style.AtlasManager.prototype.add_ =
       ++ii;
     }
   }
-  goog.asserts.fail();
+  goog.asserts.fail('Failed to add to atlasmanager');
 };
 
 
diff --git a/src/ol/style/iconstyle.js b/src/ol/style/iconstyle.js
index c25d58874e..83b9207332 100644
--- a/src/ol/style/iconstyle.js
+++ b/src/ol/style/iconstyle.js
@@ -103,7 +103,8 @@ ol.style.Icon = function(opt_options) {
   if ((!goog.isDef(src) || src.length === 0) && !goog.isNull(image)) {
     src = image.src;
   }
-  goog.asserts.assert(goog.isDef(src) && src.length > 0);
+  goog.asserts.assert(goog.isDef(src) && src.length > 0,
+      'must provide a defined and non-empty src');
 
   /**
    * @type {ol.style.ImageState}
@@ -529,8 +530,10 @@ ol.style.IconImage_.prototype.getSrc = function() {
  */
 ol.style.IconImage_.prototype.load = function() {
   if (this.imageState_ == ol.style.ImageState.IDLE) {
-    goog.asserts.assert(goog.isDef(this.src_));
-    goog.asserts.assert(goog.isNull(this.imageListenerKeys_));
+    goog.asserts.assert(goog.isDef(this.src_),
+        'this.src_ must not be undefined');
+    goog.asserts.assert(goog.isNull(this.imageListenerKeys_),
+        'no listener keys existing');
     this.imageState_ = ol.style.ImageState.LOADING;
     this.imageListenerKeys_ = [
       goog.events.listenOnce(this.image_, goog.events.EventType.ERROR,
@@ -553,7 +556,8 @@ ol.style.IconImage_.prototype.load = function() {
  * @private
  */
 ol.style.IconImage_.prototype.unlistenImage_ = function() {
-  goog.asserts.assert(!goog.isNull(this.imageListenerKeys_));
+  goog.asserts.assert(!goog.isNull(this.imageListenerKeys_),
+      'we must have listeners registered');
   goog.array.forEach(this.imageListenerKeys_, goog.events.unlistenByKey);
   this.imageListenerKeys_ = null;
 };
@@ -593,7 +597,8 @@ goog.addSingletonGetter(ol.style.IconImageCache);
  * @return {string} Cache key.
  */
 ol.style.IconImageCache.getKey = function(src, crossOrigin) {
-  goog.asserts.assert(goog.isDef(crossOrigin));
+  goog.asserts.assert(goog.isDef(crossOrigin),
+      'argument crossOrigin must be defined');
   return crossOrigin + ':' + src;
 };
 
diff --git a/src/ol/style/regularshapestyle.js b/src/ol/style/regularshapestyle.js
index 2fa0707ac5..d4e6c734b9 100644
--- a/src/ol/style/regularshapestyle.js
+++ b/src/ol/style/regularshapestyle.js
@@ -28,8 +28,9 @@ goog.require('ol.style.Stroke');
  */
 ol.style.RegularShape = function(options) {
 
-  goog.asserts.assert(goog.isDef(options.radius) ||
-      goog.isDef(options.radius1));
+  goog.asserts.assert(
+      goog.isDef(options.radius) || goog.isDef(options.radius1),
+      'must provide either "radius" or "radius1"');
 
   /**
    * @private
diff --git a/src/ol/style/style.js b/src/ol/style/style.js
index 23bd55d93f..7dbdf4ec8c 100644
--- a/src/ol/style/style.js
+++ b/src/ol/style/style.js
@@ -156,14 +156,16 @@ ol.style.Style.prototype.setGeometry = function(geometry) {
     this.geometryFunction_ = function(feature) {
       var result = feature.get(geometry);
       if (goog.isDefAndNotNull(result)) {
-        goog.asserts.assertInstanceof(result, ol.geom.Geometry);
+        goog.asserts.assertInstanceof(result, ol.geom.Geometry,
+            'feature geometry must be an ol.geom.Geometry instance');
       }
       return result;
     };
   } else if (goog.isNull(geometry)) {
     this.geometryFunction_ = ol.style.defaultGeometryFunction;
   } else if (goog.isDef(geometry)) {
-    goog.asserts.assertInstanceof(geometry, ol.geom.Geometry);
+    goog.asserts.assertInstanceof(geometry, ol.geom.Geometry,
+        'geometry must be an ol.geom.Geometry instance');
     this.geometryFunction_ = function() {
       return geometry;
     };
@@ -218,7 +220,8 @@ ol.style.createStyleFunction = function(obj) {
     if (goog.isArray(obj)) {
       styles = obj;
     } else {
-      goog.asserts.assertInstanceof(obj, ol.style.Style);
+      goog.asserts.assertInstanceof(obj, ol.style.Style,
+          'obj geometry must be an ol.style.Style instance');
       styles = [obj];
     }
     styleFunction = goog.functions.constant(styles);
@@ -358,6 +361,7 @@ ol.style.GeometryFunction;
  * @return {ol.geom.Geometry|undefined} Geometry to render.
  */
 ol.style.defaultGeometryFunction = function(feature) {
-  goog.asserts.assert(!goog.isNull(feature));
+  goog.asserts.assert(!goog.isNull(feature),
+      'feature must not be null');
   return feature.getGeometry();
 };
diff --git a/src/ol/tilecoord.js b/src/ol/tilecoord.js
index e2aa66b747..09f7da088f 100644
--- a/src/ol/tilecoord.js
+++ b/src/ol/tilecoord.js
@@ -60,7 +60,8 @@ ol.tilecoord.createFromQuadKey = function(quadKey) {
  */
 ol.tilecoord.createFromString = function(str) {
   var v = str.split('/');
-  goog.asserts.assert(v.length === 3);
+  goog.asserts.assert(v.length === 3,
+      'must provide a string in "z/x/y" format, got "%s"', str);
   v = goog.array.map(v, function(e, i, a) {
     return parseInt(e, 10);
   });
diff --git a/src/ol/tilegrid/tilegrid.js b/src/ol/tilegrid/tilegrid.js
index 8807e6e657..f3f39ccf28 100644
--- a/src/ol/tilegrid/tilegrid.js
+++ b/src/ol/tilegrid/tilegrid.js
@@ -44,7 +44,7 @@ ol.tilegrid.TileGrid = function(options) {
   this.resolutions_ = options.resolutions;
   goog.asserts.assert(goog.array.isSorted(this.resolutions_, function(a, b) {
     return b - a;
-  }, true));
+  }, true), 'resolutions must be sorted in descending order');
 
   /**
    * @protected
@@ -65,11 +65,13 @@ ol.tilegrid.TileGrid = function(options) {
   this.origins_ = null;
   if (goog.isDef(options.origins)) {
     this.origins_ = options.origins;
-    goog.asserts.assert(this.origins_.length == this.resolutions_.length);
+    goog.asserts.assert(this.origins_.length == this.resolutions_.length,
+        'number of origins and resolutions must be equal');
   }
   goog.asserts.assert(
       (goog.isNull(this.origin_) && !goog.isNull(this.origins_)) ||
-      (!goog.isNull(this.origin_) && goog.isNull(this.origins_)));
+      (!goog.isNull(this.origin_) && goog.isNull(this.origins_)),
+      'either origin or origins must be configured, never both');
 
   /**
    * @private
@@ -78,7 +80,8 @@ ol.tilegrid.TileGrid = function(options) {
   this.tileSizes_ = null;
   if (goog.isDef(options.tileSizes)) {
     this.tileSizes_ = options.tileSizes;
-    goog.asserts.assert(this.tileSizes_.length == this.resolutions_.length);
+    goog.asserts.assert(this.tileSizes_.length == this.resolutions_.length,
+        'number of tileSizes and resolutions must be equal');
   }
 
   /**
@@ -90,7 +93,8 @@ ol.tilegrid.TileGrid = function(options) {
       goog.isNull(this.tileSizes_) ? ol.DEFAULT_TILE_SIZE : undefined;
   goog.asserts.assert(
       (!goog.isDef(this.tileSize_) && !goog.isNull(this.tileSizes_)) ||
-      (goog.isDef(this.tileSize_) && goog.isNull(this.tileSizes_)));
+      (goog.isDef(this.tileSize_) && goog.isNull(this.tileSizes_)),
+      'either tileSize or tileSizes must be configured, never both');
 
   /**
    * @private
@@ -99,7 +103,8 @@ ol.tilegrid.TileGrid = function(options) {
   this.widths_ = null;
   if (goog.isDef(options.widths)) {
     this.widths_ = options.widths;
-    goog.asserts.assert(this.widths_.length == this.resolutions_.length);
+    goog.asserts.assert(this.widths_.length == this.resolutions_.length,
+        'number of widths and resolutions must be equal');
   }
 
 };
@@ -175,8 +180,11 @@ ol.tilegrid.TileGrid.prototype.getOrigin = function(z) {
   if (!goog.isNull(this.origin_)) {
     return this.origin_;
   } else {
-    goog.asserts.assert(!goog.isNull(this.origins_));
-    goog.asserts.assert(this.minZoom <= z && z <= this.maxZoom);
+    goog.asserts.assert(!goog.isNull(this.origins_),
+        'origins cannot be null if origin is null');
+    goog.asserts.assert(this.minZoom <= z && z <= this.maxZoom,
+        'given z is not in allowed range (%s <= %s <= %s)',
+        this.minZoom, z, this.maxZoom);
     return this.origins_[z];
   }
 };
@@ -188,7 +196,9 @@ ol.tilegrid.TileGrid.prototype.getOrigin = function(z) {
  * @api stable
  */
 ol.tilegrid.TileGrid.prototype.getResolution = function(z) {
-  goog.asserts.assert(this.minZoom <= z && z <= this.maxZoom);
+  goog.asserts.assert(this.minZoom <= z && z <= this.maxZoom,
+      'given z is not in allowed range (%s <= %s <= %s)',
+      this.minZoom, z, this.maxZoom);
   return this.resolutions_[z];
 };
 
@@ -378,7 +388,9 @@ ol.tilegrid.TileGrid.prototype.getTileCoordForCoordAndZ =
  */
 ol.tilegrid.TileGrid.prototype.getTileCoordResolution = function(tileCoord) {
   goog.asserts.assert(
-      this.minZoom <= tileCoord[0] && tileCoord[0] <= this.maxZoom);
+      this.minZoom <= tileCoord[0] && tileCoord[0] <= this.maxZoom,
+      'z of given tilecoord is not in allowed range (%s <= %s <= %s',
+      this.minZoom, tileCoord[0], this.maxZoom);
   return this.resolutions_[tileCoord[0]];
 };
 
@@ -411,8 +423,11 @@ ol.tilegrid.TileGrid.prototype.getTileSize = function(z) {
   if (goog.isDef(this.tileSize_)) {
     return this.tileSize_;
   } else {
-    goog.asserts.assert(!goog.isNull(this.tileSizes_));
-    goog.asserts.assert(this.minZoom <= z && z <= this.maxZoom);
+    goog.asserts.assert(!goog.isNull(this.tileSizes_),
+        'tileSizes cannot be null if tileSize is null');
+    goog.asserts.assert(this.minZoom <= z && z <= this.maxZoom,
+        'z is not in allowed range (%s <= %s <= %s',
+        this.minZoom, z, this.maxZoom);
     return this.tileSizes_[z];
   }
 };
@@ -425,7 +440,9 @@ ol.tilegrid.TileGrid.prototype.getTileSize = function(z) {
  */
 ol.tilegrid.TileGrid.prototype.getWidth = function(z) {
   if (!goog.isNull(this.widths_)) {
-    goog.asserts.assert(this.minZoom <= z && z <= this.maxZoom);
+    goog.asserts.assert(this.minZoom <= z && z <= this.maxZoom,
+        'z is not in allowed range (%s <= %s <= %s',
+        this.minZoom, z, this.maxZoom);
     return this.widths_[z];
   }
 };
diff --git a/src/ol/tilegrid/wmtstilegrid.js b/src/ol/tilegrid/wmtstilegrid.js
index 9f381c1682..e00e786399 100644
--- a/src/ol/tilegrid/wmtstilegrid.js
+++ b/src/ol/tilegrid/wmtstilegrid.js
@@ -20,7 +20,9 @@ goog.require('ol.tilegrid.TileGrid');
 ol.tilegrid.WMTS = function(options) {
 
   goog.asserts.assert(
-      options.resolutions.length == options.matrixIds.length);
+      options.resolutions.length == options.matrixIds.length,
+      'options resolutions and matrixIds must have equal length (%s == %s)',
+      options.resolutions.length, options.matrixIds.length);
 
   /**
    * @private
@@ -47,7 +49,8 @@ goog.inherits(ol.tilegrid.WMTS, ol.tilegrid.TileGrid);
  * @return {string} MatrixId..
  */
 ol.tilegrid.WMTS.prototype.getMatrixId = function(z) {
-  goog.asserts.assert(0 <= z && z < this.matrixIds_.length);
+  goog.asserts.assert(0 <= z && z < this.matrixIds_.length,
+      'attempted to retrive matrixId for illegal z (%s)', z);
   return this.matrixIds_[z];
 };
 
@@ -113,7 +116,9 @@ ol.tilegrid.WMTS.createFromCapabilitiesMatrixSet =
             metersPerUnit);
         var tileWidth = elt[tileWidthPropName];
         var tileHeight = elt[tileHeightPropName];
-        goog.asserts.assert(tileWidth == tileHeight);
+        goog.asserts.assert(tileWidth == tileHeight,
+            'square tiles are assumed, tileWidth (%s) ==  tileHeight (%s)',
+            tileWidth, tileHeight);
         tileSizes.push(tileWidth);
         widths.push(elt['MatrixWidth']);
       });
diff --git a/src/ol/tilerange.js b/src/ol/tilerange.js
index 2a2b51b61d..47ecd29103 100644
--- a/src/ol/tilerange.js
+++ b/src/ol/tilerange.js
@@ -59,7 +59,8 @@ ol.TileRange.boundingTileRange = function(var_args) {
     tileCoordZ = tileCoord[0];
     tileCoordX = tileCoord[1];
     tileCoordY = tileCoord[2];
-    goog.asserts.assert(tileCoordZ == tileCoord0Z);
+    goog.asserts.assert(tileCoordZ == tileCoord0Z,
+        'passed tilecoords all have the same Z-value');
     tileRange.minX = Math.min(tileRange.minX, tileCoordX);
     tileRange.maxX = Math.max(tileRange.maxX, tileCoordX);
     tileRange.minY = Math.min(tileRange.minY, tileCoordY);
diff --git a/src/ol/view.js b/src/ol/view.js
index 37bbdb3c86..5fba81032a 100644
--- a/src/ol/view.js
+++ b/src/ol/view.js
@@ -275,7 +275,8 @@ ol.View.prototype.getHints = function() {
  * @api
  */
 ol.View.prototype.calculateExtent = function(size) {
-  goog.asserts.assert(this.isDef());
+  goog.asserts.assert(this.isDef(),
+      'the view was not defined (had no center and/or resolution)');
   var center = this.getCenter();
   var resolution = this.getResolution();
   var minX = center[0] - resolution * size[0] / 2;
@@ -344,7 +345,9 @@ ol.View.prototype.getResolutionForValueFunction = function(opt_power) {
       function(value) {
         var resolution = maxResolution / Math.pow(power, value * max);
         goog.asserts.assert(resolution >= minResolution &&
-            resolution <= maxResolution);
+            resolution <= maxResolution,
+            'calculated resolution outside allowed bounds (%s <= %s <= %s)',
+            minResolution, resolution, maxResolution);
         return resolution;
       });
 };
@@ -383,7 +386,8 @@ ol.View.prototype.getValueForResolutionFunction = function(opt_power) {
       function(resolution) {
         var value =
             (Math.log(maxResolution / resolution) / Math.log(power)) / max;
-        goog.asserts.assert(value >= 0 && value <= 1);
+        goog.asserts.assert(value >= 0 && value <= 1,
+            'calculated value (%s) ouside allowed range (0-1)', value);
         return value;
       });
 };
@@ -393,7 +397,8 @@ ol.View.prototype.getValueForResolutionFunction = function(opt_power) {
  * @return {olx.ViewState} View state.
  */
 ol.View.prototype.getState = function() {
-  goog.asserts.assert(this.isDef());
+  goog.asserts.assert(this.isDef(),
+      'the view was not defined (had no center and/or resolution)');
   var center = /** @type {ol.Coordinate} */ (this.getCenter());
   var projection = this.getProjection();
   var resolution = /** @type {number} */ (this.getResolution());
@@ -483,7 +488,7 @@ ol.View.prototype.fitGeometry = function(geometry, size, opt_options) {
 
   // calculate rotated extent
   var rotation = this.getRotation();
-  goog.asserts.assert(goog.isDef(rotation));
+  goog.asserts.assert(goog.isDef(rotation), 'rotation was not defined');
   var cosAngle = Math.cos(-rotation);
   var sinAngle = Math.sin(-rotation);
   var minRotX = +Infinity;
@@ -602,9 +607,11 @@ goog.exportProperty(
  * @return {number} New value.
  */
 ol.View.prototype.setHint = function(hint, delta) {
-  goog.asserts.assert(0 <= hint && hint < this.hints_.length);
+  goog.asserts.assert(0 <= hint && hint < this.hints_.length,
+      'illegal hint (%s), must be between 0 and %s', hint, this.hints_.length);
   this.hints_[hint] += delta;
-  goog.asserts.assert(this.hints_[hint] >= 0);
+  goog.asserts.assert(this.hints_[hint] >= 0,
+      'Hint at %s must be positive, was %s', hint, this.hints_[hint]);
   return this.hints_[hint];
 };
 
@@ -764,7 +771,8 @@ ol.View.createRotationConstraint_ = function(options) {
     } else if (goog.isNumber(constrainRotation)) {
       return ol.RotationConstraint.createSnapToN(constrainRotation);
     } else {
-      goog.asserts.fail();
+      goog.asserts.fail(
+          'illegal option for constrainRotation (%s)', constrainRotation);
       return ol.RotationConstraint.none;
     }
   } else {
diff --git a/src/ol/webgl/context.js b/src/ol/webgl/context.js
index 616a2d7048..4b78795b3c 100644
--- a/src/ol/webgl/context.js
+++ b/src/ol/webgl/context.js
@@ -93,7 +93,8 @@ ol.webgl.Context = function(canvas, gl) {
   // use the OES_element_index_uint extension if available
   if (this.hasOESElementIndexUint) {
     var ext = gl.getExtension('OES_element_index_uint');
-    goog.asserts.assert(!goog.isNull(ext));
+    goog.asserts.assert(!goog.isNull(ext),
+        'Failed to get extension "OES_element_index_uint"');
   }
 
   goog.events.listen(this.canvas_, ol.webgl.WebGLContextEventType.LOST,
@@ -122,7 +123,8 @@ ol.webgl.Context.prototype.bindBuffer = function(target, buf) {
     var buffer = gl.createBuffer();
     gl.bindBuffer(target, buffer);
     goog.asserts.assert(target == goog.webgl.ARRAY_BUFFER ||
-        target == goog.webgl.ELEMENT_ARRAY_BUFFER);
+        target == goog.webgl.ELEMENT_ARRAY_BUFFER,
+        'target is supposed to be an ARRAY_BUFFER or ELEMENT_ARRAY_BUFFER');
     var /** @type {ArrayBufferView} */ arrayBuffer;
     if (target == goog.webgl.ARRAY_BUFFER) {
       arrayBuffer = new Float32Array(arr);
@@ -147,7 +149,8 @@ ol.webgl.Context.prototype.bindBuffer = function(target, buf) {
 ol.webgl.Context.prototype.deleteBuffer = function(buf) {
   var gl = this.getGL();
   var bufferKey = goog.getUid(buf);
-  goog.asserts.assert(bufferKey in this.bufferCache_);
+  goog.asserts.assert(bufferKey in this.bufferCache_,
+      'attempted to delete uncached buffer');
   var bufferCacheEntry = this.bufferCache_[bufferKey];
   if (!gl.isContextLost()) {
     gl.deleteBuffer(bufferCacheEntry.buffer);
@@ -231,7 +234,8 @@ ol.webgl.Context.prototype.getShader = function(shaderObject) {
     }
     goog.asserts.assert(
         gl.getShaderParameter(shader, goog.webgl.COMPILE_STATUS) ||
-        gl.isContextLost());
+        gl.isContextLost(),
+        'illegal state, shader not compiled or context lost');
     this.shaderCache_[shaderKey] = shader;
     return shader;
   }
@@ -266,7 +270,8 @@ ol.webgl.Context.prototype.getProgram = function(
     }
     goog.asserts.assert(
         gl.getProgramParameter(program, goog.webgl.LINK_STATUS) ||
-        gl.isContextLost());
+        gl.isContextLost(),
+        'illegal state, shader not linked or context lost');
     this.programCache_[programKey] = program;
     return program;
   }
diff --git a/src/ol/xml.js b/src/ol/xml.js
index 5f2a92b42d..908e6bbb9e 100644
--- a/src/ol/xml.js
+++ b/src/ol/xml.js
@@ -137,7 +137,8 @@ ol.xml.getLocalNameIE_ = function(node) {
     return localName;
   }
   var baseName = node.baseName;
-  goog.asserts.assert(goog.isDefAndNotNull(baseName));
+  goog.asserts.assert(goog.isDefAndNotNull(baseName),
+      'Failed to get localName/baseName of node %s', node);
   return baseName;
 };
 
@@ -362,10 +363,12 @@ ol.xml.makeArrayExtender = function(valueReader, opt_this) {
       function(node, objectStack) {
         var value = valueReader.call(opt_this, node, objectStack);
         if (goog.isDef(value)) {
-          goog.asserts.assert(goog.isArray(value));
+          goog.asserts.assert(goog.isArray(value),
+              'valueReader function is expected to return an array of values');
           var array = /** @type {Array.<*>} */
               (objectStack[objectStack.length - 1]);
-          goog.asserts.assert(goog.isArray(array));
+          goog.asserts.assert(goog.isArray(array),
+              'objectStack is supposed to be an array of arrays');
           goog.array.extend(array, value);
         }
       });
@@ -389,7 +392,8 @@ ol.xml.makeArrayPusher = function(valueReader, opt_this) {
             node, objectStack);
         if (goog.isDef(value)) {
           var array = objectStack[objectStack.length - 1];
-          goog.asserts.assert(goog.isArray(array));
+          goog.asserts.assert(goog.isArray(array),
+              'objectStack is supposed to be an array of arrays');
           array.push(value);
         }
       });
@@ -427,7 +431,8 @@ ol.xml.makeReplacer = function(valueReader, opt_this) {
  */
 ol.xml.makeObjectPropertyPusher =
     function(valueReader, opt_property, opt_this) {
-  goog.asserts.assert(goog.isDef(valueReader));
+  goog.asserts.assert(goog.isDef(valueReader),
+      'undefined valueReader, expected function(this: T, Node, Array.<*>)');
   return (
       /**
        * @param {Node} node Node.
@@ -441,7 +446,8 @@ ol.xml.makeObjectPropertyPusher =
               (objectStack[objectStack.length - 1]);
           var property = goog.isDef(opt_property) ?
               opt_property : node.localName;
-          goog.asserts.assert(goog.isObject(object));
+          goog.asserts.assert(goog.isObject(object),
+              'entity from stack was not an object');
           var array = goog.object.setIfUndefined(object, property, []);
           array.push(value);
         }
@@ -458,7 +464,8 @@ ol.xml.makeObjectPropertyPusher =
  */
 ol.xml.makeObjectPropertySetter =
     function(valueReader, opt_property, opt_this) {
-  goog.asserts.assert(goog.isDef(valueReader));
+  goog.asserts.assert(goog.isDef(valueReader),
+      'undefined valueReader, expected function(this: T, Node, Array.<*>)');
   return (
       /**
        * @param {Node} node Node.
@@ -472,7 +479,8 @@ ol.xml.makeObjectPropertySetter =
               (objectStack[objectStack.length - 1]);
           var property = goog.isDef(opt_property) ?
               opt_property : node.localName;
-          goog.asserts.assert(goog.isObject(object));
+          goog.asserts.assert(goog.isObject(object),
+              'entity from stack was not an object');
           object[property] = value;
         }
       });
@@ -507,10 +515,12 @@ ol.xml.makeChildAppender = function(nodeWriter, opt_this) {
     nodeWriter.call(goog.isDef(opt_this) ? opt_this : this,
         node, value, objectStack);
     var parent = objectStack[objectStack.length - 1];
-    goog.asserts.assert(goog.isObject(parent));
+    goog.asserts.assert(goog.isObject(parent),
+        'entity from stack was not an object');
     var parentNode = parent.node;
     goog.asserts.assert(ol.xml.isNode(parentNode) ||
-        ol.xml.isDocument(parentNode));
+        ol.xml.isDocument(parentNode),
+        'expected parentNode %s to be a Node or a Document', parentNode);
     parentNode.appendChild(node);
   };
 };
@@ -569,7 +579,8 @@ ol.xml.makeSimpleNodeFactory = function(opt_nodeName, opt_namespaceURI) {
       function(value, objectStack, opt_nodeName) {
         var context = objectStack[objectStack.length - 1];
         var node = context.node;
-        goog.asserts.assert(ol.xml.isNode(node) || ol.xml.isDocument(node));
+        goog.asserts.assert(ol.xml.isNode(node) || ol.xml.isDocument(node),
+            'expected node %s to be a Node or a Document', node);
         var nodeName = fixedNodeName;
         if (!goog.isDef(nodeName)) {
           nodeName = opt_nodeName;
@@ -578,7 +589,7 @@ ol.xml.makeSimpleNodeFactory = function(opt_nodeName, opt_namespaceURI) {
         if (!goog.isDef(opt_namespaceURI)) {
           namespaceURI = node.namespaceURI;
         }
-        goog.asserts.assert(goog.isDef(nodeName));
+        goog.asserts.assert(goog.isDef(nodeName), 'nodeName was undefined');
         return ol.xml.createElementNS(namespaceURI, nodeName);
       }
   );