workers-rs-mcp

An example MCP (Model Context Protocol) server written in Rust, running on Cloudflare Workers.

The server compiles to WebAssembly and runs on Cloudflare's edge infrastructure, handling MCP JSON-RPC requests over HTTP.

How it works

HTTP routing is handled by Axum via the workers-rs SDK. MCP protocol logic is handled by the mcpserver crate.

Endpoints

Method	Path	Description
GET	/	Server name and version
GET	/healthz	Health check — returns OK
POST	/mcp	MCP JSON-RPC endpoint

Session management

• initialize requests generate a new mcp-session-id (UUID v4) returned in the response header
• All subsequent requests should include the mcp-session-id header

Tools

Includes one example tool:

• echo — echoes the input message back to the caller

Getting started

Prerequisites

• Rust with the wasm32-unknown-unknown target:

  rustup target add wasm32-unknown-unknown

• Wrangler CLI:

  npm install -g wrangler

Local development

wrangler dev

Deploy to Cloudflare Workers

wrangler deploy

Pushing to main also deploys automatically via GitHub Actions (requires CLOUDFLARE_API_TOKEN and CLOUDFLARE_ACCOUNT_ID secrets).

Adding tools

1. Implement the ToolHandler trait in src/lib.rs:

struct MyToolHandler;

#[async_trait]
impl ToolHandler for MyToolHandler {
    async fn call(&self, args: Value, _context: Value) -> Result<ToolResult, McpError> {
        // your logic here
        Ok(text_result("result".to_string()))
    }
}

2. Register the tool with the MCP server:

mcp_router.handle_tool("my-tool", Arc::new(MyToolHandler));

3. Add the tool schema to mcp/tools.json.