Bring your own agent

Run your existing agent with M3 while keeping its model, tools, and vendor configuration. M3 launches it as a subprocess through the Agent Client Protocol (ACP). You install and manage the executable.

Choose the task that matches your setup:

• Connect an ACP-compatible agent when an existing agent already speaks ACP.
• Expose your custom agent through ACP when your agent uses another interface and you will provide a small ACP process.

M3 passes your MCP servers to the agent for a session and records its messages, tool calls, results, and lifecycle frames. Assertions against captured MCP responses check what the server returned. Agent-reported tool updates describe the agent's actions and may lack a matching server response.

The ACP reference covers manifest fields, session selection, environment isolation, tool-policy evidence, cancellation, and failures. Compare ACP with native harnesses in agent harness compatibility.