crimson-crab-mcp-template

Claude-powered MCP server in Rust (starter template)

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.

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