MCP Sniffer

What is MCP Sniffer?

MCP Sniffer captures network traffic between MCP clients and servers. It runs as a reverse proxy between the client and server, capturing request and response payloads that can be visualized in a web UI, similar to the Network tab in Chrome DevTools.

How to use MCP Sniffer?

Install via pipx install mcp-sniffer, then run the server using mcp-sniffer --listen-port <port> --upstream-port <port>. Configure host and port settings via command-line options or environment variables. Access the web UI at the default address http://127.0.0.1:8888.

Key features of MCP Sniffer

• Acts as a reverse proxy between MCP client and server.
• Captures request and response payloads in real time.
• Web UI for visualizing captured traffic.
• Configurable listen, upstream, and web UI hosts/ports.
• Supports environment variables for all configuration options.
• Log level can be adjusted via --log-level.

Use cases of MCP Sniffer

• Debugging MCP client-server communication.
• Inspecting MCP protocol payloads during development.
• Monitoring MCP traffic for integration testing.

FAQ from MCP Sniffer

What does MCP Sniffer do?

It sits as a reverse proxy between an MCP client and server, recording all request and response payloads, and displays them in a web interface for inspection.

How do I install MCP Sniffer?

Install it with pipx install mcp-sniffer. pipx is recommended for isolated Python application installation.

How do I configure MCP Sniffer?

Use command-line flags like --listen-port, --upstream-port, --web-ui-host, and --web-ui-port, or set the corresponding environment variables (LISTEN_PORT, UPSTREAM_PORT, etc.).

Where do I view captured traffic?

Open a browser to http://127.0.0.1:8888 (or the configured web UI host/port) to see the web interface.

Can I change the log level?

Yes, use --log-level (e.g., INFO, DEBUG) or set the LOG_LEVEL environment variable.