MCP Toolkit

mcp-toolkit

Shared machinery for a family of standalone MCP tool servers.

Each server (hex-mcp, ssh-mcp, eval-mcp, …) is a thin crate: implement ToolGroup, call run. Everything else lives here, so a fix lands in every server at once:

• CLI — --transport, --single-tool, --timeout, --bind, --auth-token, --list-tools, all with env-var equivalents.
• Transports — stdio and MCP Streamable HTTP, via the official rmcp SDK.
• --single-tool — collapses every tool into one dispatching tool for clients that cap how many they accept.
• Timeouts — a timeout argument on every tool, clamped to --max-timeout.
• Auth — bearer token on the HTTP transports; refuses to start without one unless --allow-unauthenticated is passed.

Usage

use mcp_toolkit::{ServerOptions, ToolDef, ToolGroup, ToolOutput, ToolResult};
use async_trait::async_trait;
use serde_json::{Value, json};

struct Greeter;

#[async_trait]
impl ToolGroup for Greeter {
    fn tools(&self) -> Vec<ToolDef> {
        vec![ToolDef::new("greet", "Say hello.", json!({ "type": "object" }))]
    }
    async fn call(&self, _name: &str, _args: Value) -> ToolResult<ToolOutput> {
        Ok(ToolOutput::text("hello"))
    }
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let options = ServerOptions::parse();
    mcp_toolkit::run("greeter", env!("CARGO_PKG_VERSION"), Arc::new(Greeter), options).await?;
    Ok(())
}

Why a ToolGroup trait rather than rmcp's macros

ToolGroup is plain data plus an async function, deliberately independent of rmcp. That means a tool crate can be unit-tested without standing up a protocol server, and a host process can embed the tools directly — which is how omni-mcp consumes them, as library calls rather than sidecar subprocesses.

--single-tool also needs to synthesise a tool at runtime from the others, which the attribute macros cannot express.

Notes

--transport sse is accepted as an alias for http. The standalone SSE transport was deprecated in the MCP specification in favour of Streamable HTTP, which uses SSE for its streaming responses.

Development

./scripts/build.sh

Runs cargo fmt --check, cargo clippy -D warnings (max 100 lines per function) and the tests (which enforce max 1000 lines per file).

License

Unlicense (public domain).