CrateDocs MCP Usage Guide

This guide explains how to use the CrateDocs MCP server with different types of clients.

Client Integration

Using with MCP-compatible LLMs

Any LLM client that follows the Model Context Protocol (MCP) can connect to this documentation server. The LLM will gain the ability to:

Look up documentation for any Rust crate
Search the crates.io registry for libraries
Get documentation for specific items within crates

Command-Line Client

For testing purposes, you can use a simple command-line client like this one:

use mcp_client::{Client, transport::StdioTransport};

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // Create a client using stdio transport
    let transport = StdioTransport::new();
    let mut client = Client::new(transport);
    
    // Connect to the server
    client.connect().await?;
    
    // Example: Looking up the 'tokio' crate
    let response = client.call_tool(
        "lookup_crate", 
        serde_json::json!({
            "crate_name": "tokio"
        })
    ).await?;
    
    println!("Documentation response: {}", response[0].text());
    
    Ok(())
}

Web Client

When using the Axum SSE mode, you can connect to the server using a simple web client:

// Connect to the SSE endpoint
const eventSource = new EventSource('http://127.0.0.1:8080/sse');

// Get the session ID from the initial connection
let sessionId;
eventSource.addEventListener('endpoint', (event) => {
    sessionId = event.data.split('=')[1];
    console.log(`Connected with session ID: ${sessionId}`);
});

// Handle messages from the server
eventSource.addEventListener('message', (event) => {
    const data = JSON.parse(event.data);
    console.log('Received response:', data);
});

// Function to send a tool request
async function callTool(toolName, args) {
    const response = await fetch(`http://127.0.0.1:8080/sse?sessionId=${sessionId}`, {
        method: 'POST',
        headers: {
            'Content-Type': 'application/json',
        },
        body: JSON.stringify({
            jsonrpc: '2.0',
            method: 'call_tool',
            params: {
                name: toolName,
                arguments: args
            },
            id: 1,
        }),
    });
    
    return response.ok;
}

// Example: Search for async crates
callTool('search_crates', { query: 'async runtime', limit: 5 });

Example Workflows

Helping an LLM Understand a New Crate

LLM client connects to the documentation server
User asks a question involving an unfamiliar crate
LLM uses lookup_crate to get general documentation
LLM uses lookup_item to get specific details on functions/types
LLM can now provide an accurate response about the crate

Helping Find the Right Library

User asks "What's a good crate for async HTTP requests?"
LLM uses search_crates with relevant keywords
LLM reviews the top results and their descriptions
LLM uses lookup_crate to get more details on promising options
LLM provides a recommendation with supporting information

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