Building Custom Agents

What a custom agent is

A custom agent is a saved agent mode a person or workspace owns. It is a directory agents/<key>/ in their plugins repository with two files: agent.ts (the config: label, description, color, runtime, MCP servers, tools) and instructions.md (its system prompt, layered on top of Amp's base prompt). Once saved and not a draft, it shows up in the agent picker of every new thread, and threads that run it get its instructions plus a generated list of its MCP servers and how to call them.

The manage_custom_agents tool reads and writes those files. It has four actions:

• list: every agent the person can see, whether they may write workspace agents, the workspace name, and the MCP servers configured for them (id, name, scope, connected).
• get: one agent's full config and instructions.
• put: create or fully replace one agent. Send the complete agent every time, not a diff.
• delete: remove one agent. Only after the person explicitly asks.