Show HN: Mcpsnoop – Wireshark for MCP (transparent proxy and live TUI) Developer Kerlenton released mcpsnoop, an open-source transparent proxy and terminal UI that captures live MCP (Model Context Protocol) traffic between AI clients and servers, enabling debugging of real tool calls. The tool addresses limitations of the official MCP Inspector by sitting in the actual data path, offering features like replay, capability inspection, and hung-call detection. It is available via Go install, Homebrew, or prebuilt binaries. Wireshark for MCP. A transparent proxy that shows every real tool call between your AI client and your MCP servers, live in your terminal. The official MCP Inspector https://github.com/modelcontextprotocol/inspector connects as its own client. It never sees the traffic between your client Claude Desktop, Cursor, Claude Code and your server. A breakpoint in your own server only fires once a request arrives. It can't show you the call the real client never made, or made with arguments you didn't expect. So when a tool silently isn't called, capabilities don't line up, or a call just hangs, you're back to tail -ing a log in /tmp and guessing. mcpsnoop sits in the real data path instead, so you can debug the actual MCP traffic between your client and server. Wrap your server command with it and watch every JSON-RPC frame in a live terminal UI as your real client and server talk. Want to see it first, with nothing to set up? Run mcpsnoop demo for a scripted session that plays into the live UI. To use it for real, wrap your server in your client's MCP config: { "mcpServers": { "my-server": { "command": "mcpsnoop", "args": "--", "node", "build/index.js" } }} Everything after -- is the command that normally launches your server here, a TypeScript build run with node . Swap in whatever you already use, like python server.py , npx -y @scope/server , or a compiled binary. Use your client as usual, then open the UI: mcpsnoop No flags, no socket paths, no startup order to remember. The shim and the UI find each other on their own, and the UI backfills past sessions from disk, so it doesn't matter whether you open it before or after your client. For a streamable-HTTP server, run mcpsnoop as a reverse proxy and point your client at it: mcpsnoop http --target http://localhost:3000/mcp --listen :7000 No server of your own to test against? docs/DEMO.md /kerlenton/mcpsnoop/blob/main/docs/DEMO.md walks through pointing Claude at a published test server through mcpsnoop. Live JSON-RPC stream. Requests, responses, notifications and server stderr, colour-coded, with errors and slow calls flagged, including tool-level result.isError , not just JSON-RPC errors. Replay. Re-run any captured tool call against a fresh, isolated copy of the server. The fastest loop for iterating on a tool. Capability inspector c . See exactly what the client and server agreed on at the handshake. Frame inspector enter . Full, pretty-printed JSON with in-frame search. Hung-call detection. In-flight requests show PENDING with a live timer, so a stuck tool is obvious at a glance. A real filter query. Narrow the stream with tool: , status: , dir: , kind: , id: or plain text. | MCP Inspector | mcp-trace | mcpsnoop | | |---|---|---|---| | Sees your real client↔server traffic | no | yes | yes | | Interactive terminal UI | no | yes | yes | | Zero-config, no flags or ordering | no | no | yes | | Capability inspector | partial | no | yes | | Replay a captured call | no | no | yes | | Single binary, no runtime deps | no | varies | yes | go install github.com/kerlenton/mcpsnoop/cmd/mcpsnoop@latest Or with Homebrew https://brew.sh : brew tap kerlenton/mcpsnoop brew install mcpsnoop Recent Homebrew gates third-party taps; if it refuses, trust the tap once with brew trust kerlenton/mcpsnoop and re-run the install. A tap-free brew install mcpsnoop no tap, no trust needs Homebrew core, which only accepts projects past a notability bar stars, forks, watchers . If you'd find that handy, a star on the repo helps it qualify. Or grab a prebuilt binary for your platform from the Releases https://github.com/kerlenton/mcpsnoop/releases page. The official Inspector connects as a second client, off to the side. mcpsnoop sits in the actual pipe, so it sees exactly what your real client and server say to each other, whatever the server is written in. It's two roles in one binary: mcpsnoop --