repack-logs-mcp

An MCP (Model Context Protocol) server for tailing Re.Pack/Rspack dev server logs. Enables AI assistants like Claude to query build logs, find errors, and monitor compilation status.

How It Works

This package provides three components:

1. RepackLogsPlugin - An Rspack/Webpack plugin that writes build logs to a JSON file
2. MCP Server - Watches the log file and provides tools for AI assistants to query logs
3. Client Logger - A lightweight logger for React Native apps that sends runtime logs to the MCP server

Installation

npm install -g repack-logs-mcp
# or use directly with npx
npx repack-logs-mcp /path/to/.repack-logs.json

Setup

Step 1: Add the Plugin to Your Rspack Config

Add the RepackLogsPlugin to your rspack.config.mjs (or rspack.config.js):

import { RepackLogsPlugin } from 'repack-logs-mcp/plugin';

export default {
  // ... your existing config
  plugins: [
    // ... your existing plugins
    new RepackLogsPlugin({
      // Path to write logs (default: '.repack-logs.json')
      outputPath: '/absolute/path/to/.repack-logs.json',
      // Clear logs on each build start (default: true)
      clearOnStart: true,
    }),
  ],
};

Example with Re.Pack:

import * as Repack from '@callstack/repack';
import { RepackLogsPlugin } from 'repack-logs-mcp/plugin';

export default Repack.defineRspackConfig({
  // ... your config
  plugins: [
    new Repack.RepackPlugin(),
    new RepackLogsPlugin({
      outputPath: '/Users/yourname/project/.repack-logs.json',
    }),
  ],
});

Step 2: Add Runtime Logging (Optional)

To capture runtime logs (console.log from your app), you need to add a small client script that intercepts console calls and sends them to the MCP server.

Step 2a: Create the client file

Create a file called mcp-client.js in your React Native app's root directory (next to index.js):

/**
 * MCP Console Capture Client
 * Intercepts console.log/warn/error and sends to MCP server
 */

var SERVER_URL = 'http://localhost:9090';
var logBuffer = [];
var flushTimer = null;
var BATCH_INTERVAL = 1000;
var originalConsole = {
  log: console.log,
  warn: console.warn,
  error: console.error,
  debug: console.debug,
  info: console.info
};

function flushLogs() {
  if (flushTimer) {
    clearTimeout(flushTimer);
    flushTimer = null;
  }
  if (logBuffer.length === 0) return;

  var logs = logBuffer.slice();
  logBuffer = [];

  fetch(SERVER_URL + '/logs', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ logs: logs })
  }).catch(function() {});
}

function formatArg(arg) {
  if (typeof arg === 'string') return arg;
  if (arg instanceof Error) return arg.name + ': ' + arg.message;
  try {
    return JSON.stringify(arg);
  } catch (e) {
    return String(arg);
  }
}

function createInterceptor(type, original) {
  return function() {
    var args = Array.prototype.slice.call(arguments);
    original.apply(console, args);

    var tag = 'console';
    var message = args.map(formatArg).join(' ');

    if (typeof args[0] === 'string') {
      var match = args[0].match(/^\[([^\]]+)\]/);
      if (match) tag = match[1];
    }

    var entry = {
      type: type,
      message: message,
      tag: tag,
      timestamp: new Date().toISOString()
    };

    if (args.length > 1) {
      try {
        entry.data = args.length === 2 ? args[1] : args.slice(1);
      } catch (e) {}
    }

    logBuffer.push(entry);
    if (!flushTimer) {
      flushTimer = setTimeout(flushLogs, BATCH_INTERVAL);
    }
  };
}

function enableConsoleCapture(options) {
  options = options || {};
  if (options.serverUrl) SERVER_URL = options.serverUrl;

  console.log = createInterceptor('info', originalConsole.log);
  console.info = createInterceptor('info', originalConsole.info);
  console.warn = createInterceptor('warn', originalConsole.warn);
  console.error = createInterceptor('error', originalConsole.error);
  console.debug = createInterceptor('debug', originalConsole.debug);
}

function disableConsoleCapture() {
  console.log = originalConsole.log;
  console.info = originalConsole.info;
  console.warn = originalConsole.warn;
  console.error = originalConsole.error;
  console.debug = originalConsole.debug;
}

module.exports = {
  enableConsoleCapture: enableConsoleCapture,
  disableConsoleCapture: disableConsoleCapture
};

Step 2b: Enable capture in your app

Add this to your index.js (before AppRegistry.registerComponent):

// Enable console.log capture for MCP debugging (only in dev)
if (__DEV__) {
  try {
    const { enableConsoleCapture } = require('./mcp-client');
    enableConsoleCapture();
  } catch (e) {
    // MCP client not available, skip
  }
}

Step 2c: Check the runtime server port

Run get_status to see which port the runtime server is using:

Runtime Log Server:
  Port: 9090
  URL: http://localhost:9090

If the port is different from 9090 (e.g., 9093), update SERVER_URL in mcp-client.js to match.

That's it! Now ALL your existing console.log calls are automatically sent to the MCP server.

The capture:

• Intercepts console.log, console.warn, console.error, console.debug
• Extracts tags from [TagName] patterns (e.g., console.log('[MyComponent] hello'))
• Still outputs to Metro console (so you see logs there too)
• Batches logs for efficiency (sends every 1 second)
• Only runs in development mode

Step 3: Configure the MCP Server

Point the MCP server to the same log file path used in your plugin config.

Tools Provided

Tool	Description
get_build_logs	Get recent build logs with filters (type, limit, time, issuer, search)
get_runtime_logs	Get runtime logs from the React Native app (console.log output)
get_errors	Get only errors and warnings
clear_logs	Clear the in-memory buffer
get_status	Show watcher status, runtime server port, and statistics

Configuration

The log file path can be set via:

1. CLI argument (highest priority):

   npx repack-logs-mcp /path/to/.repack-logs.json
   

2. Environment variable:

   REPACK_LOG_FILE=/path/to/.repack-logs.json npx repack-logs-mcp
   

3. Default: .repack-logs.json in current directory

Plugin Options

Option	Description	Default
outputPath	Path to the log file	.repack-logs.json
clearOnStart	Clear log file on each build start	true

Environment Variables (MCP Server)

Variable	Description	Default
REPACK_LOG_FILE	Path to the build log file	.repack-logs.json
REPACK_MAX_LOGS	Maximum logs to keep in memory	1000
REPACK_RUNTIME_PORT	HTTP port for runtime log server	9090

Claude Code Integration

Add to your Claude Code MCP settings (~/.claude/settings.json or project settings):

{
  "mcpServers": {
    "repack-logs": {
      "command": "npx",
      "args": ["repack-logs-mcp", "/path/to/your/project/.repack-logs.json"]
    }
  }
}

Then ask Claude things like:

• "What are the recent build logs?"
• "Show me the runtime logs"
• "Are there any build errors?"
• "Show me warnings from the last build"
• "What's the status of the log watcher?"

Usage Examples

Get recent logs

Tool: get_build_logs
Args: { "limit": 10 }

Filter by type

Tool: get_build_logs
Args: { "types": ["error", "warn"], "limit": 20 }

Search logs

Tool: get_build_logs
Args: { "search": "Cannot find module" }

Get errors only

Tool: get_errors
Args: { "limit": 10 }

Get runtime logs

Tool: get_runtime_logs
Args: { "limit": 50 }

Filter runtime logs by tag

Tool: get_runtime_logs
Args: { "tag": "MyComponent", "limit": 20 }

Search runtime logs

Tool: get_runtime_logs
Args: { "search": "error", "types": ["error", "warn"] }

Development

# Install dependencies
npm install

# Build
npm run build

# Test with MCP Inspector
npx @modelcontextprotocol/inspector node dist/index.js .repack-logs.json

License

MIT