`rtb-mcp` v0.1¶

Thin wrapper over the official rmcp SDK. Walks rtb_app::command::BUILTIN_COMMANDS for entries marked mcp_exposed = true and registers each as an MCP tool. Each tools/call invocation runs the underlying Command::run against a clone of the host App.

Public API¶

use rtb_app::app::App;
use rtb_mcp::{McpServer, Transport};

# async fn run(app: App) -> Result<(), rtb_mcp::McpError> {
McpServer::new(app, Transport::Stdio).serve().await
# }

The crate ships three public items:

[McpServer] — owns the tool registry, drives the rmcp service loop.
[Transport] — Stdio / Sse { bind } / Http { bind }. Stdio is the default and the only fully-implemented variant in v0.1.
[McpError] — Transport / Protocol / Command variants, each carrying enough context for telemetry routing.

Opting a command into MCP¶

Command::mcp_exposed and Command::mcp_input_schema are default trait methods on rtb_app::command::Command:

impl Command for MyTool {
    // …
    fn mcp_exposed(&self) -> bool { true }
    fn mcp_input_schema(&self) -> Option<serde_json::Value> {
        Some(serde_json::to_value(schemars::schema_for!(MyArgs)).unwrap())
    }
}

Both default to false / None, so existing impls are untouched.

CLI¶

mcp is registered into BUILTIN_COMMANDS like any other built-in. Two subcommands:

Command	Behaviour
`mcp serve [--transport stdio\\|sse\\|http] [--bind ADDR]`	Run the server until the transport closes or `App::shutdown` fires.
`mcp list`	Print every exposed tool's name + description + JSON schema as one JSON object per line.

mcp serve defaults to --transport stdio. The Sse and Http variants currently return an McpError::Transport saying so — streamable-HTTP wiring lands in a v0.3.x point release.

Transports¶

Variant	Status	Notes
`Transport::Stdio`	shipped	The expected entry point for "spawn me as a subprocess" MCP clients.
`Transport::Sse { bind }`	stub	Surfaces `McpError::Transport`. v0.3.x.
`Transport::Http { bind }`	stub	Surfaces `McpError::Transport`. v0.3.x.

McpServer::serve_with_pipe(read, write) is the test seam — pass any AsyncRead + AsyncWrite pair (e.g. tokio::io::duplex) and the rmcp service loop will run against it. The integration test for the crate (tests/t9_s1_roundtrip.rs) uses this to drive a real MCP client against the server in-process.

Failure modes¶

Transport(String) — bind / accept / I/O failure.
Protocol(String) — protocol violations rtb-mcp raises (unknown tool name on dispatch, malformed arguments).
Command { command, message } — the underlying Command::run returned an error during a tools/call. The error is forwarded to the MCP client as the call's is_error: true payload.

McpError derives Clone, thiserror::Error, and miette::Diagnostic, matching every other RTB error enum.

Spec¶

Authoritative contract: docs/development/specs/2026-05-01-rtb-mcp-v0.1.md.

rtb-mcp v0.1¶