agent-client-protocol-rmcp

rmcp integration for Agent Client Protocol MCP servers.

Overview

This crate bridges rmcp-based MCP server implementations with the runtime-agnostic MCP server framework from agent-client-protocol. It lets you define MCP tools in Rust, serve them directly, or attach them to an ACP proxy.

Attached servers are advertised with the opt-in native MCP-over-ACP transport: McpServer::Acp plus mcp/connect, mcp/message, and mcp/disconnect. This crate does not enable the core SDK's unstable_mcp_over_acp feature merely to build or directly serve a server. Enable this crate's matching unstable_mcp_over_acp feature when using with_mcp_server. Use agent-client-protocol-polyfill when the final agent accepts HTTP but not ACP-transport MCP servers.

Usage

Use the McpServerExt trait to build an MCP server with tools:

use agent_client_protocol::{ConnectTo, mcp_server::McpServer, role::mcp};
use agent_client_protocol_rmcp::McpServerExt;

async fn serve(
    client_transport: impl ConnectTo<mcp::Server>,
) -> agent_client_protocol::Result<()> {
    let server = McpServer::<mcp::Client>::builder("my-tools").build();
    server.connect_to(client_transport).await
}

Choosing mcp::Client as the counterpart makes this a standalone MCP server that implements ConnectTo<mcp::Client>.

Or create an MCP server from an rmcp service:

use agent_client_protocol::mcp_server::McpServer;
use agent_client_protocol_rmcp::McpServerExt;

let server = McpServer::from_rmcp("my-server", MyRmcpService::new);

// Use as a handler in a proxy
Proxy.builder()
    .with_mcp_server(server)
    .connect_to(transport)
    .await?;

Why a Separate Crate?

This crate is separate from agent-client-protocol to avoid coupling the core protocol crate to the rmcp dependency. This allows:

• agent-client-protocol to remain focused on the ACP protocol
• agent-client-protocol-rmcp to track rmcp updates independently
• Integrations to choose compatible agent-client-protocol and rmcp major versions explicitly

Versioning

Both agent-client-protocol and rmcp are public dependencies of this crate: their types and traits appear in its public API. A source-incompatible major release of either dependency therefore requires a major release of this crate.

Related Crates

• agent-client-protocol — Core ACP protocol types and traits
• agent-client-protocol-conductor — Proxy-chain orchestration

License

Apache-2.0