Claude-powered MCP server in Rust (starter template)

A minimal, production-ready Model Context Protocol (MCP) server, written in Rust, that exposes a single tool — ask_claude — backed by Anthropic's Claude API through the crimson-crab SDK. When an MCP client (such as Claude Desktop) calls the tool, the server sends the prompt to Claude and returns Claude's text answer.

Use it as the reference starting point for building your own Claude-powered MCP tools in Rust.

Use this template

Click Use this template on GitHub, or generate a fresh project with cargo generate:

cargo generate --git https://github.com/singhpratech/crimson-crab-mcp-template

You can also just clone it:

git clone https://github.com/singhpratech/crimson-crab-mcp-template

Quickstart

export ANTHROPIC_API_KEY=sk-ant-...
cargo run

The server communicates over stdio, so running it directly just waits for an MCP client to connect. All logging goes to stderr — stdout is reserved for the MCP protocol. Set RUST_LOG=debug for more verbose logs.

To build an optimized binary you can point a client at:

cargo build --release
# -> target/release/crimson-crab-mcp-template

Wire it into Claude Desktop

Add an entry to your Claude Desktop MCP config (claude_desktop_config.json), pointing at the built binary and passing your API key through the environment:

{
  "mcpServers": {
    "claude-via-crimson-crab": {
      "command": "/absolute/path/to/target/release/crimson-crab-mcp-template",
      "env": {
        "ANTHROPIC_API_KEY": "sk-ant-..."
      }
    }
  }
}

Restart Claude Desktop; the ask_claude tool will then be available.

What ask_claude does

Parameter	Type	Required	Description
prompt	string	yes	The prompt to send to Claude.
system	string	no	Optional system prompt.

The tool builds a Claude Messages request (defaulting to the claude-opus-4-8 model), calls the API, and returns the concatenated text of Claude's reply. Errors are returned as MCP tool errors rather than panicking. The Claude client is built once at startup and reused across calls.

Built with crimson-crab

This template is built with crimson-crab — a production-grade Rust SDK for Anthropic's Claude API. Source: https://github.com/singhpratech/crimson-crab.

License

Licensed under either of

• MIT license (LICENSE-MIT)
• Apache License, Version 2.0 (LICENSE-APACHE)

at your option.

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crimson-crab is an independent open-source project and is not affiliated with Anthropic.