Claude-powered MCP server in Rust (starter template)

Name: crimson crab mcp template
Author: singhpratech

A minimal, production-ready Model Context Protocol (MCP) server, written in Rust, backed by Anthropic's Claude API through the crimson-crab SDK. It exposes five tools: ask_claude (send a prompt, get Claude's reply), chat (multi-turn conversation), count_tokens (price a prompt without running it), list_models (enumerate the models your API key can use), and get_model (limits and metadata for one model).

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, chat, count_tokens, list_models, and get_model tools will then be available.

The tools

`ask_claude`

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

Builds a Claude Messages request (defaulting to the claude-opus-5 model), calls the API, and returns the concatenated text of Claude's reply.

`chat`

Parameter	Type	Required	Description
`messages`	`array`	yes	The conversation so far, oldest first: `{role, content}` where `role` is an enum constrained to `"user"` or `"assistant"`. Must end with a user turn.
`system`	`string`	no	Optional system prompt.
`model`	`string`	no	Model id (defaults to the `ask_claude` model).
`max_tokens`	`integer`	no	Maximum tokens to generate (default 1024).

Sends the whole message history to Claude and returns the next reply — use it instead of ask_claude when the caller needs to keep context across turns.

`count_tokens`

Parameter	Type	Required	Description
`prompt`	`string`	yes	The prompt whose token count you want.
`system`	`string`	no	Optional system prompt to include in the count.
`model`	`string`	no	Model id to count against (counts are model-specific).

Returns the number of input tokens the prompt would consume, without running it — useful for estimating cost before an expensive call.

`list_models`

Parameter	Type	Required	Description
`limit`	`integer`	no	Maximum number of models to return.

Returns the id, display name, and release date of each Claude model available to the configured API key.

`get_model`

Parameter	Type	Required	Description
`model`	`string`	yes	The model id to look up, e.g. `claude-opus-5`.

Returns the model's display name, release date, context window (max_input_tokens), and maximum output tokens.

Errors from all tools 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.

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