JavaScript Source Map Unminifier
Upload minified JavaScript code and its source map (v3) to reconstruct the original source files. Map minified positions back to original file, line, and column. Supports inline source maps and external .map files — all free, private, and no signup required.
Upload or paste a minified JavaScript file and its source map to reconstruct original source code. Supports inline source maps (/*# sourceMappingURL=data:... */) and external .map files. All processing happens in your browser — no uploads.
Source Map Summary
- src/index.js ✓
- src/utils.js ✓
Understanding Source Map Unminification
A source map maps minified code back to original source files using VLQ-encoded position mappings. When sourcesContent is present (as in this sample), the original source code can be fully reconstructed. Without sourcesContent, only position data is available and reconstruction is limited to showing where each mapping points. The source map format (v3) is defined by theSource Map Specification.
Features
Source Map Unminification
Upload minified JavaScript alongside its source map to reconstruct original source code. Maps every minified position back to its original file, line, and column with full precision.
Inline & External Source Map Support
Supports inline source maps (data:application/json;base64,...), //# sourceMappingURL= comments, and external .map file upload. Works with all major bundlers: Webpack, Rollup, Vite, ESBuild, and Terser.
Original Code Reconstruction
After mapping, browse the reconstructed original source files with correct variable names, comments, and formatting. Navigate between original files using a file explorer panel.
Detailed Position Mapping
Explore the source map's mapping data in a structured table. See every original position (file, line, column) mapped to its minified position. Copy individual mappings or export the full mapping table as JSON.
Use Cases
Debugging Production Code
When encountering a cryptic minified stack trace, use the source map to map the error back to your original source files. Quickly identify the exact line and file that caused the issue without redeploying.
Third-Party Library Inspection
Analyze minified third-party JavaScript libraries that include source maps. Reconstruct the original code to understand how a library works, identify potential security issues, or debug integration problems.
Performance Optimization
Map minified bundle output back to original source to understand which modules contribute to bundle size. Identify large dependencies, dead code, and opportunities for tree-shaking by examining reconstructed source files.
Security Auditing
Audit minified JavaScript bundles for hidden malicious code, backdoors, or suspicious dependencies. Source maps reveal the original structure, making it easier to spot obfuscated or injected code.
Legacy Code Recovery
When you've lost the original source files but have a deployed minified bundle with source maps, use this tool to reconstruct original sources. Useful for recovering code from archived or deprecated projects.
Build Pipeline Validation
After setting up a new build pipeline, verify that source maps correctly map minified output back to original sources. Validate position mappings to ensure your error tracking tools receive accurate source references.
About Source Map Unminification
What Is a Source Map?
A source map (specified by the Source Map Specification) is a file that maps minified or transpiled code back to its original source. When JavaScript is minified, variable names are shortened, whitespace is removed, and multiple files are bundled together. A source map stores a mapping of every position in the output to its original file, line, and column — enabling tools like debuggers and error trackers to show original source code instead of the minified output.
How the Unminifier Works
The JavaScript Source Map Unminifier parses your minified code and source map using the mozilla/source-map library (ported to browser-compatible JS). The tool reads the VLQ-encoded mappings in the source map, decodes them into (output_line, output_column) → (source_file, source_line, source_column) pairs, and reconstructs the original source files. Files appear in a navigable tree, and each mapping can be inspected individually in a detail table. All processing happens in your browser — no data is ever uploaded.
VLQ Encoding & Mappings
Source maps use Variable Length Quantity (VLQ) encoding to compactly store position mappings as Base64-encoded strings. Each mapping segment encodes five values: column in the generated file, original source file index, original line number, original column number, and optional original name index. The unminifier decodes these VLQ segments and presents them in a human-readable table, showing every generated position and its corresponding original position. Understanding VLQ helps you verify that your source maps are correctly generated.
Privacy & Security
This tool runs entirely in your browser. Your minified code and source maps are never uploaded to any server, stored in any database, or transmitted over the network. All parsing, decoding, and reconstruction logic executes locally on your device. There are no API calls, no analytics tracking, and no data collection of any kind. This makes it safe to use with proprietary code, internal applications, and sensitive third-party libraries that you are auditing.