atpmcp

A local MCP (Model Context Protocol) server for AT Protocol DAG-CBOR CID generation.

Overview

A standalone MCP server binary that communicates over stdio using JSON-RPC 2.0. It provides a create_record_cid tool that accepts a JSON object, serializes it to DAG-CBOR, hashes it with SHA-256, and returns the CIDv1 string. This allows AI assistants like Claude to compute content identifiers for AT Protocol records directly.

Tools

• create_record_cid: Accepts a JSON record object and returns its DAG-CBOR CID. The record is serialized using deterministic DAG-CBOR encoding, hashed with SHA-256, and returned as a CIDv1 base32 string.

Building

cargo build -p atpmcp

Claude Code Integration

Add the following to your Claude Code MCP configuration (~/.claude/claude_code_config.json):

{
  "mcpServers": {
    "atpmcp": {
      "command": "/path/to/atpmcp"
    }
  }
}

Replace /path/to/atpmcp with the absolute path to the compiled binary (e.g., target/release/atpmcp after running cargo build -p atpmcp --release).

Or, if atpmcp is already in your PATH:

tmp=$(jq '.mcpServers.atpmcp = {"command": "atpmcp"}' ~/.claude/claude_code_config.json) && echo "$tmp" > ~/.claude/claude_code_config.json

Once configured, Claude Code will have access to the create_record_cid tool and can compute CIDs for AT Protocol records during conversations.

Example usage in Claude Code

Ask Claude to compute a CID:

What is the CID for this AT Protocol record?

{
  "$type": "app.bsky.feed.post",
  "text": "Hello AT Protocol!",
  "createdAt": "2024-01-01T00:00:00.000Z"
}

Claude will call the create_record_cid tool and return the CID string.

Protocol Details

The server implements the MCP stdio transport:

• stdin: Receives newline-delimited JSON-RPC 2.0 messages
• stdout: Sends newline-delimited JSON-RPC 2.0 responses
• stderr: Tracing/logging output (controlled by RUST_LOG environment variable)

Supported methods:

License

MIT License