Source Map VLQ Decoder

Decode and encode Base64 Variable-Length Quantity (VLQ) mapping segments used in JavaScript and CSS source maps (`.map` files). Decodes VLQ strings into relative column numbers, source file indices, line numbers, and symbol indices.

Why Use This Tool?

• Source Map Debugging: Inspect and verify compiled JavaScript minified line/column mappings back to original source files.
• Build Tool Development: Debug custom source map generator plugins for Webpack, Vite, or Esbuild.
• Understand VLQ Encoding: Learn how Base64 VLQ packs multi-digit relative numbers into compact ASCII strings.

How to Use

1. Paste Base64 VLQ mapping segment (e.g. `AAAA`, `CAAC`, `EAAEE`).
2. Click Decode VLQ.
3. View parsed relative integers: Generated Column, Source File Index, Original Line, Original Column, Symbol Index.

Real Working Example

Input:

VLQ Segment: CAAC

Output Result:

Decoded Integers: [1, 0, 0, 1]
Interpretation:
- Generated Column Offset: +1
- Source File Index Offset: +0
- Original Line Offset: +0
- Original Column Offset: +1

Important Technical Details & Specifications

• Source Map Revision 3 Spec: Implements official Source Map v3 VLQ Base64 encoding/decoding rules.
• Sign-Bit & Continuation Bit Math: Decodes 5-bit VLQ payloads with 6th continuation bit.
• Local Memory Execution: Zero network overhead.

Related Developer Tools

• JavaScript Beautifier: Beautify JavaScript code.
• Base64 Encoder/Decoder: Encode and decode Base64.
• Hexdump Viewer: Render binary hex dumps.