How does VLQ decoding work in Source Maps?

Source Maps v3 encode line and column deltas as Variable-Length Quantity (VLQ) base64 strings. Each group represents generated column, source file index, original line, original column, and symbol name index.

Can I unmangle production error stack traces?

Yes. Paste any minified production stack trace into the Stack Trace Unmangler tab. The engine replaces bundle coordinates with original source files and line numbers.

Are my source maps or source code uploaded anywhere?

Never. All decoding and symbol resolution happen 100% locally in your web browser tab.

Source Map Explorer & Stack Unmangler

Decode Source Map v3 VLQ mappings, map minified line/column coordinates back to original TypeScript/JavaScript source files, and unmangle production stack traces.

100% Client-Side Privacy

Drop .map file here or click to browse

Supports Source Map v3 (.js.map, .css.map)

Version: 3

Source Files: 0 files

Symbols / Names: 0

Embedded Sources: No

Minified Line:

Minified Column:

Original File:-

Original Line:-

Original Column:-

Symbol / Identifier:-

Frequently Asked Questions

What is a Source Map?

A Source Map provides a mapping between transpiled/minified code (such as bundled JavaScript produced by esbuild, Vite, Webpack, or Rollup) and the original human-readable source code (like TypeScript or ES6).

How does the stack trace unmangler work?

It scans each line of the stack trace using regular expressions to extract filenames and line:column coordinates. It then looks up each coordinate in the decoded VLQ mappings table and substitutes original source locations.

Does this tool support 0-based and 1-based columns?

Yes. In standard Source Maps, lines are 1-based and columns are 0-based. The resolver normalizes browser DevTools convention so coordinates match exactly.

Is my source code secure?

Yes. No files or stack traces are ever transmitted over the network. 100% of processing runs in your browser.