Xdebug MCP Server

Xdebug MCP Server

An MCP (Model Context Protocol) server that provides PHP debugging capabilities through Xdebug's DBGp protocol. This allows AI assistants like Claude to directly debug PHP applications.

Features

Core Debugging

• Full Debug Control: Step into, step over, step out, continue, stop
• Breakpoints: Line breakpoints, conditional breakpoints, exception breakpoints, function call breakpoints
• Variable Inspection: View all variables, get specific variables, set variable values
• Expression Evaluation: Evaluate PHP expressions in the current context
• Stack Traces: View the full call stack
• Multiple Sessions: Debug multiple PHP scripts simultaneously
• Docker Support: Works with PHP running in Docker containers

Advanced Features

• Watch Expressions: Persistent watches that auto-evaluate on each break with change detection
• Logpoints: Log messages without stopping execution using {$var} placeholders
• Memory Profiling: Track memory usage and execution time between breakpoints
• Code Coverage: Track which lines were executed during debugging
• Request Context: Capture $_GET, $_POST, $_SESSION, $_COOKIE, headers automatically
• Step Filters: Skip vendor/library code during stepping
• Debug Profiles: Save and restore breakpoint configurations
• Session Export: Export debug sessions as JSON or HTML reports

Installation

From npm (Recommended)

npm install -g xdebug-mcp

From Source

git clone https://github.com/kpanuragh/xdebug-mcp.git
cd xdebug-mcp
npm install
npm run build

MCP Server Configuration

For Claude Code

Add the xdebug-mcp server to your MCP configuration (.mcp.json or Claude settings):

Using npm global install:

{
  "mcpServers": {
    "xdebug": {
      "command": "xdebug-mcp",
      "env": {
        "XDEBUG_PORT": "9003",
        "LOG_LEVEL": "info"
      }
    }
  }
}

Using npx:

{
  "mcpServers": {
    "xdebug": {
      "command": "npx",
      "args": ["-y", "xdebug-mcp"],
      "env": {
        "XDEBUG_PORT": "9003",
        "LOG_LEVEL": "info"
      }
    }
  }
}

With Path Mappings (for Docker)

When debugging PHP in Docker containers, you need path mappings to translate container paths to host paths:

{
  "mcpServers": {
    "xdebug": {
      "command": "xdebug-mcp",
      "env": {
        "XDEBUG_PORT": "9003",
        "PATH_MAPPINGS": "{\"/var/www/html\": \"/home/user/projects/myapp\"}",
        "LOG_LEVEL": "info"
      }
    }
  }
}

With DBGp Proxy Registration

If you already use a DBGp proxy, keep mcp-config.example.json as the default direct-listener example and start from mcp-config.proxy.example.json for proxy registration.

Proxy mode requires:

• TCP listener mode for xdebug-mcp (not XDEBUG_SOCKET_PATH)
• a unique callback port such as 9006, 9007, or 9008 for XDEBUG_PORT
• DBGP_PROXY_HOST, DBGP_PROXY_PORT, and DBGP_IDEKEY

See the DBGp Proxy Registration Guide for the full setup, multi-agent examples, and PHP/Xdebug proxy configuration.

PHP/Xdebug Configuration

php.ini (or xdebug.ini)

[xdebug]
zend_extension=xdebug

; Enable step debugging
xdebug.mode=debug

; Start debugging on every request
xdebug.start_with_request=yes

; Host where MCP server is running
; For Docker: use host.docker.internal
; For local PHP: use 127.0.0.1
xdebug.client_host=host.docker.internal

; Port where MCP server listens
xdebug.client_port=9003

; IDE key (optional, for filtering)
xdebug.idekey=mcp

Docker Compose

version: '3.8'

services:
  php:
    image: php:8.2-apache
    volumes:
      - ./src:/var/www/html
      - ./xdebug.ini:/usr/local/etc/php/conf.d/99-xdebug.ini
    extra_hosts:
      - "host.docker.internal:host-gateway"  # Required for Linux
    environment:
      - XDEBUG_MODE=debug
      - XDEBUG_CONFIG=client_host=host.docker.internal client_port=9003

Using Unix Domain Sockets

For improved performance and simplified setup on local systems, you can use Unix domain sockets instead of TCP. Unix sockets eliminate network stack overhead and are ideal for debugging on the same machine.

Benefits:

• ⚡ Lower latency (no TCP/IP stack overhead)
• 🔒 Better security (file permissions instead of port binding)
• 📦 Simpler setup (no port management)
• 🚀 Faster communication for local debugging

MCP Configuration (Unix Socket):

{
  "mcpServers": {
    "xdebug": {
      "command": "xdebug-mcp",
      "env": {
        "XDEBUG_SOCKET_PATH": "/tmp/xdebug.sock",
        "LOG_LEVEL": "info"
      }
    }
  }
}

PHP/Xdebug Configuration:

[xdebug]
zend_extension=xdebug
xdebug.mode=debug
xdebug.start_with_request=yes
xdebug.client_host=unix:///tmp/xdebug.sock

Socket File Permissions:

The socket file is created with default permissions. To restrict access, you can:

# After MCP server starts
chmod 600 /tmp/xdebug.sock

# Or use a secure directory
mkdir -p ~/.xdebug && chmod 700 ~/.xdebug
# Then set XDEBUG_SOCKET_PATH=$HOME/.xdebug/xdebug.sock

Automatic Cleanup:

When XDEBUG_SOCKET_PATH is set, the server will:

• Listen on the specified Unix socket instead of TCP port
• Automatically clean up stale socket files on startup (prevents "address in use" errors)
• Automatically clean up socket files on shutdown
• Use the same debugging tools and features as TCP mode

When to Use Unix Sockets:

• ✅ Local PHP development (best performance)
• ✅ Same-machine debugging
• ✅ High-frequency breakpoint hits
• ❌ Remote debugging (use TCP instead)

Unix socket support requested in Issue #1 by @dkd-kaehm

Available MCP Tools (41 Total)

Session Management

Breakpoints

Pending Breakpoints: You can set breakpoints before a debug session starts. These are stored as "pending breakpoints" and automatically applied when a PHP script connects with Xdebug. This is useful for setting up breakpoints before triggering a page load or script execution.

Execution Control

Inspection

Watch Expressions

Logpoints

Profiling

Code Coverage

Debug Profiles

Additional Tools

Usage Examples

Setting a Breakpoint

Use set_breakpoint with file="/var/www/html/index.php" and line=25

Conditional Breakpoint

Use set_breakpoint with file="/var/www/html/api.php", line=42, condition="$userId > 100"

Watch Expression

Use add_watch with expression="$user->email"
Use add_watch with expression="count($items)"

Logpoint

Use add_logpoint with file="/var/www/html/api.php", line=50, message="User {$userId} accessed {$endpoint}"

Inspecting Variables

Use get_variables to see all local variables
Use get_variable with name="$user" to inspect a specific variable
Use evaluate with expression="count($items)" to evaluate an expression

Capture Request Context

Use capture_request_context to see $_GET, $_POST, $_SESSION, cookies, and headers

Environment Variables

Connection Modes: TCP vs Unix Socket

Quick Decision Guide:

• 🏠 Local development? → Use Unix socket for best performance
• 🐳 Docker on same machine? → Use Unix socket with volume mount
• 🌐 Remote server? → Use TCP
• 🚀 Maximum speed? → Use Unix socket
• 📝 Don't know? → Start with TCP (default), switch to Unix socket if needed

How It Works

1. MCP Server starts and listens for Xdebug connections (TCP port 9003 or Unix socket)
2. PHP script runs with Xdebug enabled
3. Xdebug connects to the MCP server via DBGp protocol
4. AI uses MCP tools to control debugging (set breakpoints, step, inspect)
5. DBGp commands are sent to Xdebug, responses parsed and returned

┌─────────────┐     MCP/stdio      ┌─────────────┐   DBGp/TCP or    ┌─────────────┐
│   Claude    │ ◄────────────────► │  xdebug-mcp │ ◄─ Unix Socket ──► │   Xdebug    │
│  (AI Agent) │                    │   Server    │                   │  (in PHP)   │
└─────────────┘                    └─────────────┘                   └─────────────┘

Connection Options:

• TCP (Default): xdebug.client_host=127.0.0.1 + XDEBUG_PORT=9003
• Unix Socket: xdebug.client_host=unix:///tmp/xdebug.sock + XDEBUG_SOCKET_PATH=/tmp/xdebug.sock

Troubleshooting

No debug sessions appearing

1. Check that Xdebug is installed: php -v should show Xdebug
2. Verify Xdebug config: php -i | grep xdebug
3. Ensure xdebug.client_host points to the MCP server
4. For TCP: Check firewall allows connections on port 9003
5. For Unix socket: Verify socket path exists and has correct permissions: ls -la /tmp/xdebug.sock
6. Check MCP server logs: LOG_LEVEL=debug for verbose output

Connection issues with Docker

1. For Linux, add extra_hosts: ["host.docker.internal:host-gateway"]
2. Verify container can reach host: curl host.docker.internal:9003
3. Check xdebug logs in container: docker logs <container-id> | grep xdebug

Unix socket issues

1. "Address already in use": Socket file wasn't cleaned up
   • Remove manually: rm -f /tmp/xdebug.sock
   • MCP server will clean up automatically on next start
2. "Permission denied": Check socket file permissions
   • List socket: ls -la /tmp/xdebug.sock
   • Run as same user as PHP: ps aux | grep php
3. Socket path in php.ini:
   • Correct: xdebug.client_host=unix:///tmp/xdebug.sock
   • Wrong: xdebug.client_host=unix:/tmp/xdebug.sock (missing one /)

Breakpoints not hitting

1. Ensure file paths match exactly (use container paths for Docker)
2. Check breakpoint is resolved: list_breakpoints
3. Verify script execution reaches that line
4. Check that xdebug.start_with_request=yes is set
5. Try a simple file to verify basic setup works

Performance issues

1. If experiencing slow stepping, increase COMMAND_TIMEOUT:
   • Default: 30000ms (30 seconds)
   • Try: COMMAND_TIMEOUT=60000 for slower systems
2. For Unix sockets, verify socket is on fast filesystem (not network mount)
3. Check system load: top - excessive context switching slows debugging

Server won't start

1. Port in use (TCP):
   • Find process: lsof -i :9003
   • Kill it: kill -9 <pid>
2. Bad config:
   • Validate environment variables: echo $XDEBUG_SOCKET_PATH
   • Check for typos in path names
3. Permission denied:
   • For Unix socket, ensure write permission to parent directory
   • Example: mkdir -p ~/.xdebug && chmod 700 ~/.xdebug

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

MIT