DevTools failed to load source map Browser Origin: On your device Last updated 15 Oct 2026

DevTools: Failed to load source map — Could not load content for https://…/app.js.map: HTTP error: status code 404

DevTools could not download the .map file that a script or stylesheet points to, so you see minified code instead of your sources. Visitors are not affected.

Exact message you may see DevTools failed to load source mapCould not load content forHTTP error: status code 404, net::ERR_HTTP_RESPONSE_CODE_FAILUREFailed to load source map
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Seen on: Chrome Edge JavaScript Nginx

Meaning

The last line of a bundle (//# sourceMappingURL=app.js.map) tells DevTools where the map is. The warning appears when the map was not deployed, is blocked or behind auth, or when a browser extension (chrome-extension://…) ships a bad reference. It is only a debugging warning; fix it by deploying the maps, or stop emitting the comment in production.

Common causes

  • Source maps not uploaded to the server (excluded from deploy or .gitignored)
  • Server or CDN blocks .map files or requires authentication
  • Wrong publicPath/base so the map URL is wrong
  • Third-party library or extension referencing a map it does not ship
  • Maps served with the wrong path after a CDN rewrite

⚡ Quick fix

  1. Deploy the .map files next to the bundles, or turn maps off for production builds
  2. Ignore warnings from chrome-extension:// URLs — they are from extensions
  3. In DevTools Settings turn off "Enable JavaScript source maps" if you do not need them

Detailed fix by platform

JavaScript

  1. Vite: build: { sourcemap: true } (or false); webpack: devtool: 'source-map' or false; Next.js: productionBrowserSourceMaps: true

Nginx

  1. Make sure .map files are not denied: remove rules like location ~ \.map$ { return 404; } if you want maps available (or restrict them to your IP)

Chrome

  1. DevTools → Settings (F1) → Preferences → Sources → untick "Enable JavaScript source maps" to silence the warnings

How to diagnose

  1. URL — Does the .map URL open in a new tab?
  2. Origin — Own bundle or an extension/library?
  3. Build — Are maps generated and deployed?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: On your device. Errors that are often confused with or caused by this one (click to open):

$ is not defined — Console: Uncaught ReferenceError: $ is not defined (jQuery not loaded or loaded after your code) (Browser)$ is not defined404 — HTTP 404 Not Found (HTTP)404Aw, Snap! — Chrome: Aw, Snap! Something went wrong while displaying this webpage. Error code: STATUS_ACCESS_VIOLATION / SIGILL / Out of Memory (Browser)Aw, Snap!ChunkLoadError — ChunkLoadError: Loading chunk 123 failed. (JavaScript)ChunkLoadErrorExtension context invalidated — Console: Uncaught Error: Extension context invalidated (extension was updated or reloaded) (Browser)Extension context inv…Failed to find a valid digest in the 'integrity' attribute — Console: Failed to find a valid digest in the 'integrity' attribute for resource … with computed SHA-256 integrity (Browser)Failed to find a vali…MIME type not executable — Refused to execute script from 'x' because its MIME type ('text/html') is not executable (JavaScript)MIME type not executa…Module parse failed — Module parse failed: Unexpected token. You may need an appropriate loader to handle this file type (React)Module parse failedDevTools …

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