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Module acp_basics

agent_client_protocol::concepts

Module acp_basics 

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The roles in ACP: clients, agents, proxies, and conductors.

The Agent-Client Protocol defines how AI agents communicate with the applications that use them. Understanding the four roles helps you choose the right approach for what you’re building.

§Clients

A client is an application that wants to use an AI agent. Examples include:

  • IDEs like VS Code or JetBrains
  • Command-line tools
  • Web applications
  • Automation scripts

Clients send prompts to agents and receive responses. They can also handle requests from the agent (like permission requests or tool approvals).

§Agents

An agent is an AI-powered service that responds to prompts. Examples include:

  • Claude Code
  • Custom agents built with language models

Agents receive prompts, process them (typically by calling an LLM), and stream back responses. They may also request permissions, invoke tools, or ask for user input during processing.

§Proxies

A proxy sits between a client and an agent, intercepting and potentially modifying messages in both directions. Proxies are useful for:

  • Adding tools via MCP (Model Context Protocol) servers
  • Injecting system prompts or context
  • Logging and debugging
  • Filtering or transforming messages

Proxies can be chained - you can have multiple proxies between a client and an agent, each adding its own capabilities.

§Conductors

A conductor orchestrates a chain of proxies with a final agent. It:

  • Spawns and manages proxy processes
  • Routes messages through the chain
  • Handles initialization and shutdown

The agent-client-protocol-conductor crate provides a conductor implementation. Most users don’t need to implement conductors themselves - they just configure which proxies to use.

§Message Flow

Messages flow through the system like this:

Client <-> Proxy 1 <-> Proxy 2 <-> ... <-> Agent
       ^                                ^
       |                                |
       +------ Conductor manages -------+

Each arrow represents a bidirectional connection. Requests flow toward the agent, responses flow back toward the client, and notifications can flow in either direction.

§Next Steps

Now that you understand the roles, see Connections and Links to learn how to establish connections in code.