docs: add an overview to rmcp/src/lib.rs (#116)

crates/rmcp/src/lib.rs

@@ -1,3 +1,92 @@
+//! The official Rust SDK for the Model Context Protocol (MCP).
+//!
+//! The MCP is a protocol that allows AI assistants to communicate with other
+//! services. `rmcp` is the official Rust implementation of this protocol.
+//!
+//! There are two ways in which the library can be used, namely to build a
+//! server or to build a client.
+//!
+//! ## Server
+//!
+//! A server is a service that exposes capabilities. For example, a common
+//! use-case is for the server to make multiple tools available to clients such
+//! as Claude Desktop or the Cursor IDE.
+//!
+//! For example, to implement a server that has a tool that can count, you would
+//! make an object for that tool and add an implementation with the `#[tool(tool_box)]` macro:
+//!
+//! ```rust
+//! use std::sync::Arc;
+//! use rmcp::{Error as McpError, model::*, tool};
+//! use tokio::sync::Mutex;
+//!
+//! #[derive(Clone)]
+//! pub struct Counter {
+//!     counter: Arc<Mutex<i32>>,
+//! }
+//!
+//! #[tool(tool_box)]
+//! impl Counter {
+//!     fn new() -> Self {
+//!         Self {
+//!             counter: Arc::new(Mutex::new(0)),
+//!         }
+//!     }
+//!
+//!     #[tool(description = "Increment the counter by 1")]
+//!     async fn increment(&self) -> Result<CallToolResult, McpError> {
+//!         let mut counter = self.counter.lock().await;
+//!         *counter += 1;
+//!         Ok(CallToolResult::success(vec![Content::text(
+//!             counter.to_string(),
+//!         )]))
+//!     }
+//! }
+//! ```
+//!
+//! Next also implement [ServerHandler] for `Counter` and start the server inside
+//! `main` by calling `Counter::new().serve(...)`. See the examples directory in the repository for more information.
+//!
+//! ## Client
+//!
+//! A client can be used to interact with a server. Clients can be used to get a
+//! list of the available tools and to call them. For example, we can `uv` to
+//! start a MCP server in Python and then list the tools and call `git status`
+//! as follows:
+//!
+//! ```rust
+//! use anyhow::Result;
+//! use rmcp::{model::CallToolRequestParam, service::ServiceExt, transport::TokioChildProcess};
+//! use tokio::process::Command;
+//!
+//! async fn client() -> Result<()> {
+//!     let service = ()
+//!       .serve(TokioChildProcess::new(
+//!             Command::new("uvx").arg("mcp-server-git"),
+//!         )?)
+//!         .await?;
+//!
+//!     // Initialize
+//!     let server_info = service.peer_info();
+//!     println!("Connected to server: {server_info:#?}");
+//!
+//!     // List tools
+//!     let tools = service.list_tools(Default::default()).await?;
+//!     println!("Available tools: {tools:#?}");
+//!
+//!     // Call tool 'git_status' with arguments = {"repo_path": "."}
+//!     let tool_result = service
+//!         .call_tool(CallToolRequestParam {
+//!             name: "git_status".into(),
+//!             arguments: serde_json::json!({ "repo_path": "." }).as_object().cloned(),
+//!         })
+//!         .await?;
+//!     println!("Tool result: {tool_result:#?}");
+//!
+//!     service.cancel().await?;
+//!     Ok(())
+//! }
+//! ```
 mod error;
 pub use error::Error;