MCP Debug

mcp-debug is a command-line tool for debugging MCP (Model Context Protocol) servers. It helps developers inspect MCP server capabilities, debug tool integrations, and test server notifications.

Key Features

• Connect to any MCP Server: Works with servers using streamable-http transport.
• OAuth 2.1 Authentication: Full MCP authorization specification (2025-11-25) compliance with security-first defaults
  • Automatic discovery (RFC 9728 Protected Resource Metadata, RFC 8414 AS Metadata)
  • Resource Indicators (RFC 8707) for token audience binding
  • PKCE validation (required by MCP spec)
  • Dynamic Client Registration (RFC 7591) and Client ID Metadata Documents
  • Step-up authorization for runtime permission escalation
  • Intelligent scope selection (auto and manual modes)
• Interactive REPL: Explore available tools, resources, and prompts interactively.
• MCP Server Mode: Acts as an MCP server itself, allowing integration with AI assistants like Cursor.
• Verbose Logging: Detailed logging of JSON-RPC messages for in-depth debugging.
• Self-Update: Keep the tool up-to-date with a single command.
• Shell Autocompletion: Generates autocompletion scripts for Bash, Zsh, Fish, and PowerShell.

Getting Started

Installation

To build the tool from source and install it in your PATH:

go install github.com/giantswarm/mcp-debug@latest

Documentation

For detailed instructions on all features:

• ➡️ mcp-debug Usage Guide - Complete feature guide
• ➡️ OAuth 2.1 Documentation - Comprehensive OAuth authentication guide

OAuth 2.1 Quick Start

Connect to a protected MCP server with automatic discovery:

./mcp-debug --oauth --endpoint https://mcp.example.com/mcp

This automatically:

• Discovers the authorization server (RFC 9728)
• Validates PKCE support (required by MCP spec)
• Uses the official Client ID Metadata Document (CIMD)
• Falls back to Dynamic Client Registration if CIMD is not supported
• Opens your browser for authorization
• Connects with audience-bound tokens (RFC 8707)

Client ID Metadata Document (CIMD)

mcp-debug uses CIMD by default for OAuth authentication. The official client metadata is hosted at:

https://giantswarm.github.io/mcp-debug/client.json

This allows OAuth-protected MCP servers to identify mcp-debug without requiring pre-registration. The authorization server fetches the metadata from this URL and displays "MCP Debugger CLI" on the consent screen.

If you need to use a custom CIMD or disable it:

# Use a custom CIMD URL
./mcp-debug --oauth --oauth-client-id-metadata-url https://example.com/my-client.json --endpoint https://mcp.example.com/mcp

# Disable CIMD and force Dynamic Client Registration
./mcp-debug --oauth --oauth-disable-cimd --endpoint https://mcp.example.com/mcp

See the OAuth Documentation for detailed guides, examples, and troubleshooting.

Basic Examples

Connect to a server and listen for notifications:

./mcp-debug --endpoint http://localhost:8090/mcp

Start the interactive REPL:

./mcp-debug --repl

Run as an MCP server for AI assistant integration:

./mcp-debug --mcp-server

Refer to the usage guide for more advanced examples.

Contributing

Contributions are welcome! Please open an issue or submit a pull request.

License

mcp-debug is licensed under the Apache 2.0 License.