Stdio proxy (CLI)

The mcp-tap CLI binary sits between any MCP client and server over stdio, transparently intercepting JSON-RPC messages without modifying them.

Usage

mcp-tap --api-key tap_abc123 -- npx -y @modelcontextprotocol/server-github

mcp-tap --api-key tap_abc123 --endpoint https://custom.endpoint/api/v1/events -- python my_server.py

With AARM receipt signing:

mcp-tap --api-key tap_abc123 --signing-key ./private-key.pem -- node server.js

Flag	Required	Description
`--api-key <key>`	Yes	Project API key
`--endpoint <url>`	No	Custom event ingestion endpoint
`--signing-key <path>`	No	Path to Ed25519 private key PEM for AARM signing

Everything after -- is treated as the MCP server command.

Spawn

Spawns the MCP server as a child process.

Forward

Forwards stdin from the client to the server, stdout from the server to the client.

Parse

Parses JSON-RPC messages on both pipes.

Emit tool events

For tools/call requests: records the request, matches it with the response, and emits a tool_call event with source: "mcp_proxy".

Emit lifecycle events

For other MCP lifecycle methods (e.g., initialize, tools/list): emits an mcp_lifecycle event.

The proxy also works as a Python module:

python -m mcp_tap --api-key tap_abc123 -- python my_server.py