Source Map Parser

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This project implements a WebAssembly-based Source Map parser that can map JavaScript error stack traces back to source code and extract relevant context information. Developers can easily map JavaScript error stack traces back to source code for quick problem identification and resolution. This documentation aims to help developers better understand and use this tool.

MCP Integration

Note: Requires Node.js 20+ support

Option 1: Run directly with NPX

npx -y source-map-parser-mcp@latest

Option 2: Download the build artifacts

Download the corresponding version of the build artifacts from the GitHub Release page, then run:

node dist/main.es.js

Use as an npm package (bring your own MCP server)

You can embed the tools into your own MCP server process and customize behavior.

Install:

npm install source-map-parser-mcp

Minimal server (TypeScript):

import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
import {
  registerTools,
  Parser,
  type ToolsRegistryOptions,
} from 'source-map-parser-mcp';

const server = new McpServer(
  { name: 'your-org.source-map-parser', version: '0.0.1' },
  { capabilities: { tools: {} } }
);

// Optional: control context lines via env
const options: ToolsRegistryOptions = {
  contextOffsetLine:
    Number(process.env.SOURCE_MAP_PARSER_CONTEXT_OFFSET_LINE) || 1,
};

registerTools(server, options);

// Start as stdio server
const transport = new StdioServerTransport();
await server.connect(transport);

// If you need programmatic parsing without MCP:
const parser = new Parser({ contextOffsetLine: 1 });
// await parser.parseStack({ line: 10, column: 5, sourceMapUrl: 'https://...' });
// await parser.batchParseStack([{ line, column, sourceMapUrl }]);

Build and Type Declarations

This project ships both ESM and CJS builds and a single bundled TypeScript declaration file.

• Build outputs:
  • ESM: dist/index.es.js
  • CJS: dist/index.cjs.js
  • CLI entry: dist/main.es.js
  • Types: dist/index.d.ts (single bundled d.ts)

Quick build locally:

npm install
npm run build

Using types in your project:

import {
  Parser,
  registerTools,
  type ToolsRegistryOptions,
} from 'source-map-parser-mcp';

Runtime Parameter Configuration

System runtime parameters can be flexibly configured through environment variables to meet the needs of different scenarios

• SOURCE_MAP_PARSER_RESOURCE_CACHE_MAX_SIZE: Sets the maximum memory space occupied by resource cache, default is 200MB. Adjusting this value appropriately can balance performance and memory usage.
• SOURCE_MAP_PARSER_CONTEXT_OFFSET_LINE: Defines the number of context code lines to display around the error location, default is 1 line. Increasing this value provides more context information, facilitating problem diagnosis.

Example:

# Set 500MB cache and display 3 lines of context
export SOURCE_MAP_PARSER_RESOURCE_CACHE_MAX_SIZE=500
export SOURCE_MAP_PARSER_CONTEXT_OFFSET_LINE=3
npx -y source-map-parser-mcp@latest

Feature Overview

1. Stack Parsing: Parse the corresponding source code location based on provided line number, column number, and Source Map file.
2. Batch Processing: Support parsing multiple stack traces simultaneously and return batch results.
3. Context Extraction: Extract context code for a specified number of lines to help developers better understand the environment where errors occur.
4. Context Lookup: Look up original source code context for specific compiled code positions.
5. Source Unpacking: Extract all source files and their content from source maps.

MCP Service Tool Description

operating_guide

Get usage instructions for the MCP service. Provides information on how to use the MCP service through chat interaction.

parse_stack

Parse stack information by providing stack traces and Source Map addresses.

Request Example

• stacks: Stack information including line number, column number, and Source Map address.
  • line: Line number, required.
  • column: Column number, required.
  • sourceMapUrl: Source Map address, required.

{
  "stacks": [
    {
      "line": 10,
      "column": 5,
      "sourceMapUrl": "https://example.com/source.map"
    }
  ]
}

Response Example

{
  "content": [
    {
      "type": "text",
      "text": "[{\"success\":true,\"token\":{\"line\":10,\"column\":5,\"sourceCode\":[{\"line\":8,\"isStackLine\":false,\"raw\":\"function foo() {\"},{\"line\":9,\"isStackLine\":false,\"raw\":\"  console.log('bar');\"},{\"line\":10,\"isStackLine\":true,\"raw\":\"  throw new Error('test');\"},{\"line\":11,\"isStackLine\":false,\"raw\":\"}\"}],\"src\":\"index.js\"}}]"
    }
  ]
}

lookup_context

Look up original source code context for a specific line and column position in compiled/minified code.

Request Example

• line: The line number in the compiled code (1-based), required.
• column: The column number in the compiled code, required.
• sourceMapUrl: The URL of the source map file, required.
• contextLines: Number of context lines to include (default: 5), optional.

{
  "line": 42,
  "column": 15,
  "sourceMapUrl": "https://example.com/app.js.map",
  "contextLines": 5
}

Response Example

{
  "content": [
    {
      "type": "text",
      "text": "{\"filePath\":\"src/utils.js\",\"targetLine\":25,\"contextLines\":[{\"lineNumber\":23,\"content\":\"function calculateSum(a, b) {\"},{\"lineNumber\":24,\"content\":\"  if (a < 0 || b < 0) {\"},{\"lineNumber\":25,\"content\":\"    throw new Error('Negative numbers not allowed');\"},{\"lineNumber\":26,\"content\":\"  }\"},{\"lineNumber\":27,\"content\":\"  return a + b;\"}]}"
    }
  ]
}

unpack_sources

Extract all source files and their content from a source map.

Request Example

• sourceMapUrl: The URL of the source map file to unpack, required.

{
  "sourceMapUrl": "https://example.com/bundle.js.map"
}

Response Example

{
  "content": [
    {
      "type": "text",
      "text": "{\"sources\":{\"src/index.js\":\"import { utils } from './utils.js';\\nconsole.log('Hello World!');\",\"src/utils.js\":\"export const utils = { add: (a, b) => a + b };\"},\"sourceRoot\":\"/\",\"file\":\"bundle.js\",\"totalSources\":2}"
    }
  ]
}

Parsing Result Description

• success: Indicates whether the parsing was successful.
• token: The Token object returned when parsing is successful, containing source code line number, column number, context code, and other information.
• error: Error information returned when parsing fails.

Example Run

System Prompt

According to actual needs, you can use system prompts to guide the model on how to parse stack information. For security or performance reasons, some teams may not want to expose Source Maps directly to the browser for parsing, but instead process the upload path of the Source Map. For example, converting the path bar-special.js to special/bar.js.map. In this case, you can instruct the model to perform path conversion through prompt rules.

Here is an example:

# Error Stack Trace Parsing Rules

When performing source map parsing, please follow these rules:

1. If the URL contains `special`, the file should be parsed into the `special/` directory, while removing `-special` from the filename.
2. All source map files are stored in the following CDN directory:  
   `https://cdn.jsdelivr.net/gh/MasonChow/source-map-parser-mcp@main/example/`

## Examples

- Source map address for `bar-special.js`:  
  `https://cdn.jsdelivr.net/gh/MasonChow/source-map-parser-mcp@main/example/special/bar.js.map`

Runtime Example

Error Stack

Uncaught Error: This is a error
    at foo-special.js:49:34832
    at ka (foo-special.js:48:83322)
    at Vs (foo-special.js:48:98013)
    at Et (foo-special.js:48:97897)
    at Vs (foo-special.js:48:98749)
    at Et (foo-special.js:48:97897)
    at Vs (foo-special.js:48:98059)
    at sv (foo-special.js:48:110550)
    at foo-special.js:48:107925
    at MessagePort.Ot (foo-special.js:25:1635)

FAQ

1. WebAssembly Module Loading Failure

If the tool returns the following error message, please troubleshoot as follows:

parser init error: WebAssembly.instantiate(): invalid value type 'externref', enable with --experimental-wasm-reftypes @+86