kerlenton/mcpsnoop

go install github.com/kerlenton/mcpsnoop/cmd/mcpsnoop@latest
brew install mcpsnoop
Prebuilt binaries for every platform on the Releases page

Usage

• •Wrap a stdio server: mcpsnoop -- node build/index.js (swap in your client's MCP config)
• •Proxy a streamable-HTTP server: mcpsnoop http --target http://localhost:3000/mcp --listen :7000
• •Open the live TUI: mcpsnoop (sessions backfill from disk); mcpsnoop demo to try
• •Gate CI: mcpsnoop check --fail-on error,invalid,warn session.jsonl

Key features

• ✓Transparent stdio shim + streamable-HTTP reverse proxy; sees the real client↔server traffic, whatever language the server is in
• ✓Flags hung calls, stream errors, stray output corrupting the stream, malformed JSON-RPC frames, and tool definition drift after approval
• ✓mcpsnoop check for CI (error/invalid/warn/pending/mismatch/drift/deprecated signals), JUnit output, --expect-tool/--forbid-tool/--max-duration
• ✓Session export to json/html/text/har/otlp; live OTLP streaming; mcpsnoop diff between sessions; mcpsnoop baseline for trusted tool definitions
• ✓Key/path/value-based secret redaction; tool summary shows per-tool context cost (definitions/results) in bytes
• ✓Capability inspector, call replay, filtering (tool:/method:/status:/kind:), remote SSH tunnel viewing

Best for

Debugging and verifying MCP servers/agents in the real data path — catching calls the model never made, hung calls, malformed frames, and schema drift.

Caveats

• ⚠Runs the server command you wrap — only wrap servers you trust; run untrusted ones in a container
• ⚠Captured frames can include prompts, tool arguments, credentials, and results — opt in to redaction (best effort)
• ⚠Live SSH tunnel needs Linux/macOS on both ends; Windows uses the post-mortem log copy instead
• ⚠The 2026-07-28 MCP revision removed server-initiated requests; deprecated features (Roots, Sampling, Logging) are flagged, not errors