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The MCP proxy sits between any MCP client and server, transparently forwarding all JSON-RPC messages while logging every tools/call request and response to the audit trail.

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Setup

plog proxy --command "npx @modelcontextprotocol/server-filesystem /path/to/dir"
plog proxy --command "npx @modelcontextprotocol/server-filesystem /tmp" --agent-id my-agent
The proxy:
  1. Spawns the given command as a child process
  2. Intercepts all JSON-RPC messages on stdin/stdout
  3. Logs tools/call requests and responses to ProvenLog
  4. Forwards everything transparently — the client and server are unaware of the proxy

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What gets captured

EventAction TypeDetails
Tool call requestTOOL_CALLTool name, input arguments
Tool call responseTOOL_RESULTTool output, duration

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Use cases

  • Audit MCP tool usage in Claude Desktop, Cursor, or any MCP client
  • Monitor which tools agents are calling and what data they access
  • Create a verifiable record of all MCP interactions without modifying the server