Crate mcplease 

A simple framework for writing Model Context Protocol servers.

The types and headers modules are unconditional — both sides of the protocol need all of them, and they cost nothing but serde. headers is shared rather than split because a client deriving what to send and a server checking what arrived are the same derivation; splitting them is how they drift. Everything else sits behind a feature naming either a side of the protocol or a transport; see the [features] table in Cargo.toml. The default is everything.

A server that speaks a transport this crate does not implement wants default-features = false, features = ["server"]: that is traits, the tools! macro, and handle_request, which answers a decoded request without doing any I/O.

A client wants default-features = false, features = ["client"]: the client module, which is the same split from the other side — it builds requests and classifies the messages that arrive, and leaves framing, connections, and authorization to the transport. It pulls no dependencies this crate does not already have.

The dependencies re-exported at the root are there for the macros to name and for a downstream tool to use without duplicating the version requirement. Each is present only under the features that pull it.

Re-exports

pub use anyhow;server or session

pub use clap;cli

pub use dirs;cli or session

pub use fieldwork;server

pub use log;

pub use schemars;server

pub use serde;

pub use serde_json;

pub use shellexpand;cli or session

Modules

clientclient

Transport-agnostic client protocol — the mirror of handle_request.

headers

The standard request headers HTTP transports carry from 2026-07-28 onward (SEP-2243), and the validation a server owes them.

sessionsession

traitsserver

types

Serialization types for the Model Context Protocol.

Macros

server_infoserver

structured_outputserver

Implement ToolOutput for types that derive JsonSchema and Serialize, using the spec’s recommended lossless shape.

toolsserver

Structs

ServerConfigserver

Everything the serve loop needs beyond the tools themselves.

Constants

DEFAULT_TOOLS_TTL_MSserver

How long a client may consider a tools/list result fresh.

Functions

handle_requestserver

Answer one request. Dispatch is stateless: every supported revision’s entry points are answerable at any time, so both the initialize handshake (revisions through 2025-11-25) and the stateless server/discover flow (2026-07-28) work against the same loop.

runcli

servestdio

Read messages from stdin until EOF, answering each request on stdout.