diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2850e95c..69c3051c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@
 - Fix Firefox open file that stopped working due to react upgrade
 - Fix issue with missing bottom error panel
 - Fixed headers in left panes (Layers list and Layer editor) to remain visible when scrolling
+- Fix error when using a source from localhost
 - _...Add new stuff here..._
 
 ## 3.0.0
diff --git a/src/components/InputUrl.tsx b/src/components/InputUrl.tsx
index 3cf3810d..3add35ee 100644
--- a/src/components/InputUrl.tsx
+++ b/src/components/InputUrl.tsx
@@ -3,55 +3,31 @@ import InputString from "./InputString";
 import SmallError from "./SmallError";
 import { Trans, type WithTranslation, withTranslation } from "react-i18next";
 import { type TFunction } from "i18next";
+import { ErrorType, validate } from "../libs/urlopen";
 
-function validate(url: string, t: TFunction): JSX.Element | undefined {
-  if (url === "") {
-    return;
-  }
-
-  let error;
-  const getProtocol = (url: string) => {
-    try {
-      const urlObj = new URL(url);
-      return urlObj.protocol;
-    }
-    catch (_err) {
-      return undefined;
-    }
-  };
-  const protocol = getProtocol(url);
-  const isSsl = window.location.protocol === "https:";
-
-  if (!protocol) {
-    if (isSsl) {
-      error = (
+function errorTypeToJsx(errorType: ErrorType | undefined, t: TFunction): JSX.Element | undefined {
+  switch (errorType) {
+    case ErrorType.EmptyHttpsProtocol:
+      return (
         <SmallError>
           <Trans t={t}>Must provide protocol: <code>https://</code></Trans>
         </SmallError>
       );
-    } else {
-      error = (
+    case ErrorType.EmptyHttpOrHttpsProtocol:
+      return (
         <SmallError>
           <Trans t={t}>Must provide protocol: <code>http://</code> or <code>https://</code></Trans>
         </SmallError>
       );
-    }
+    case ErrorType.CorsError:
+      return (
+        <SmallError>
+          <Trans t={t}>CORS policy won&apos;t allow fetching resources served over http from https, use a <code>https://</code> domain</Trans>
+        </SmallError>
+      );
+    default:
+      return undefined;
   }
-  else if (
-    protocol &&
-    protocol === "http:" &&
-    window.location.protocol === "https:"
-  ) {
-    error = (
-      <SmallError>
-        <Trans t={t}>
-          CORS policy won&apos;t allow fetching resources served over http from https, use a <code>https://</code> domain
-        </Trans>
-      </SmallError>
-    );
-  }
-
-  return error;
 }
 
 export type FieldUrlProps = {
@@ -71,7 +47,7 @@ export type FieldUrlProps = {
 type InputUrlInternalProps = FieldUrlProps & WithTranslation;
 
 type InputUrlState = {
-  error?: React.ReactNode
+  error?: ErrorType
 };
 
 class InputUrlInternal extends React.Component<InputUrlInternalProps, InputUrlState> {
@@ -82,20 +58,20 @@ class InputUrlInternal extends React.Component<InputUrlInternalProps, InputUrlSt
   constructor (props: InputUrlInternalProps) {
     super(props);
     this.state = {
-      error: validate(props.value, props.t),
+      error: validate(props.value),
     };
   }
 
   onInput = (url: string) => {
     this.setState({
-      error: validate(url, this.props.t),
+      error: validate(url),
     });
     if (this.props.onInput) this.props.onInput(url);
   };
 
   onChange = (url: string) => {
     this.setState({
-      error: validate(url, this.props.t),
+      error: validate(url),
     });
     this.props.onChange(url);
   };
@@ -109,7 +85,7 @@ class InputUrlInternal extends React.Component<InputUrlInternalProps, InputUrlSt
           onChange={this.onChange}
           aria-label={this.props["aria-label"]}
         />
-        {this.state.error}
+        {errorTypeToJsx(this.state.error, this.props.t)}
       </div>
     );
   }
diff --git a/src/libs/urlopen.test.ts b/src/libs/urlopen.test.ts
new file mode 100644
index 00000000..3dc4c5db
--- /dev/null
+++ b/src/libs/urlopen.test.ts
@@ -0,0 +1,153 @@
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { validate, ErrorType } from "./urlopen";
+
+// Mock window.location if not in browser environment
+const mockLocation = {
+  protocol: "http:",
+  hostname: "localhost",
+};
+
+Object.defineProperty(global, "window", {
+  value: {
+    location: mockLocation,
+  },
+  writable: true,
+});
+
+describe("validate", () => {
+  let originalProtocol: string;
+
+  beforeEach(() => {
+    // Save original protocol
+    originalProtocol = window.location.protocol;
+  });
+
+  afterEach(() => {
+    // Restore original protocol
+    Object.defineProperty(window.location, "protocol", {
+      writable: true,
+      value: originalProtocol,
+    });
+  });
+
+  describe("when URL is empty", () => {
+    it("should return ErrorType.None", () => {
+      expect(validate("")).toBe(ErrorType.None);
+    });
+  });
+
+  describe("when window.location.protocol is https:", () => {
+    beforeEach(() => {
+      Object.defineProperty(window.location, "protocol", {
+        writable: true,
+        value: "https:",
+      });
+    });
+
+    it("should return EmptyHttpsProtocol when URL has no protocol", () => {
+      expect(validate("example.com")).toBe(ErrorType.EmptyHttpsProtocol);
+      expect(validate("www.example.com/path")).toBe(ErrorType.EmptyHttpsProtocol);
+    });
+
+    it("should return None for valid https URLs", () => {
+      expect(validate("https://example.com")).toBe(ErrorType.None);
+      expect(validate("https://www.example.com/path")).toBe(ErrorType.None);
+    });
+
+    it("should return CorsError for http URLs pointing to non-local hosts", () => {
+      expect(validate("http://example.com")).toBe(ErrorType.CorsError);
+      expect(validate("http://api.example.com/endpoint")).toBe(ErrorType.CorsError);
+    });
+
+    it("should return None for http URLs pointing to localhost", () => {
+      expect(validate("http://localhost")).toBe(ErrorType.None);
+      expect(validate("http://localhost:3000")).toBe(ErrorType.None);
+      expect(validate("http://127.0.0.1")).toBe(ErrorType.None);
+      expect(validate("http://127.0.0.1:8080")).toBe(ErrorType.None);
+      expect(validate("http://127.255.255.255")).toBe(ErrorType.None);
+    });
+
+    it("should return None for http URLs pointing to IPv6 localhost", () => {
+      expect(validate("http://[::1]")).toBe(ErrorType.None);
+      expect(validate("http://[::1]:3000")).toBe(ErrorType.None);
+    });
+
+    it("should return None for other protocols", () => {
+      expect(validate("ftp://example.com")).toBe(ErrorType.None);
+      expect(validate("ws://example.com")).toBe(ErrorType.None);
+      expect(validate("wss://example.com")).toBe(ErrorType.None);
+    });
+  });
+
+  describe("when window.location.protocol is http:", () => {
+    beforeEach(() => {
+      Object.defineProperty(window.location, "protocol", {
+        writable: true,
+        value: "http:",
+      });
+    });
+
+    it("should return EmptyHttpOrHttpsProtocol when URL has no protocol", () => {
+      expect(validate("example.com")).toBe(ErrorType.EmptyHttpOrHttpsProtocol);
+      expect(validate("www.example.com/path")).toBe(ErrorType.EmptyHttpOrHttpsProtocol);
+    });
+
+    it("should return None for valid http URLs", () => {
+      expect(validate("http://example.com")).toBe(ErrorType.None);
+      expect(validate("http://www.example.com/path")).toBe(ErrorType.None);
+    });
+
+    it("should return None for valid https URLs", () => {
+      expect(validate("https://example.com")).toBe(ErrorType.None);
+      expect(validate("https://www.example.com/path")).toBe(ErrorType.None);
+    });
+
+    it("should return None for localhost URLs", () => {
+      expect(validate("http://localhost")).toBe(ErrorType.None);
+      expect(validate("http://127.0.0.1")).toBe(ErrorType.None);
+    });
+  });
+
+  describe("edge cases", () => {
+    it("should handle URLs with ports", () => {
+      Object.defineProperty(window.location, "protocol", {
+        writable: true,
+        value: "https:",
+      });
+
+      expect(validate("https://example.com:8443")).toBe(ErrorType.None);
+      expect(validate("http://example.com:8080")).toBe(ErrorType.CorsError);
+      expect(validate("http://localhost:3000")).toBe(ErrorType.None);
+    });
+
+    it("should handle URLs with paths and query strings", () => {
+      Object.defineProperty(window.location, "protocol", {
+        writable: true,
+        value: "https:",
+      });
+
+      expect(validate("https://example.com/path?query=value")).toBe(ErrorType.None);
+      expect(validate("http://example.com/path?query=value")).toBe(ErrorType.CorsError);
+    });
+
+    it("should handle malformed URLs that cannot be parsed", () => {
+      Object.defineProperty(window.location, "protocol", {
+        writable: true,
+        value: "https:",
+      });
+
+      expect(validate("not a url at all")).toBe(ErrorType.EmptyHttpsProtocol);
+      expect(validate("://")).toBe(ErrorType.EmptyHttpsProtocol);
+    });
+
+    it("should handle localhost variations case-insensitively", () => {
+      Object.defineProperty(window.location, "protocol", {
+        writable: true,
+        value: "https:",
+      });
+
+      expect(validate("http://LOCALHOST")).toBe(ErrorType.None);
+      expect(validate("http://LocalHost:3000")).toBe(ErrorType.None);
+    });
+  });
+});
diff --git a/src/libs/urlopen.ts b/src/libs/urlopen.ts
index a793f081..86c27a8b 100644
--- a/src/libs/urlopen.ts
+++ b/src/libs/urlopen.ts
@@ -25,3 +25,45 @@ export async function loadStyleUrl(styleUrl: string): Promise<StyleSpecification
     return style.emptyStyle;
   }
 }
+
+export const enum ErrorType {
+  None,
+  EmptyHttpsProtocol,
+  EmptyHttpOrHttpsProtocol,
+  CorsError
+}
+
+function getProtocolSafe(url: string): { protocol?: string, isLocal?: boolean } {
+  try {
+    const urlObj = new URL(url);
+    const { protocol, hostname } = urlObj;
+    const isLocal = /^(localhost|\[::1\]|127(.[0-9]{1,3}){3})/i.test(hostname);
+    return { protocol, isLocal };
+  }
+  catch (_err) {
+    return {};
+  }
+};
+
+export function validate(url: string): ErrorType {
+  if (url === "") {
+    return ErrorType.None;
+  }
+
+  const { protocol, isLocal } = getProtocolSafe(url);
+  const isSsl = window.location.protocol === "https:";
+
+  if (!protocol && isSsl) {
+    return ErrorType.EmptyHttpsProtocol;
+  }
+  if (!protocol) {
+    return ErrorType.EmptyHttpOrHttpsProtocol;
+  }
+  if (protocol &&
+    protocol === "http:" &&
+    window.location.protocol === "https:" &&
+    !isLocal) {
+    return ErrorType.CorsError;
+  }
+  return ErrorType.None;
+}