mcp-broadcast

@cryptoapis-io/mcp-broadcast

MCP server for Crypto APIs Broadcast product. Submit locally signed transactions to the blockchain.

API Version: Compatible with Crypto APIs version 2024-12-12

Features

• Broadcast signed transaction hex to any supported blockchain
• Supports EVM (Ethereum, Ethereum Classic, BSC, Polygon, Avalanche (C-Chain), Arbitrum, Base, Optimism, Tron)
• Supports UTXO (Bitcoin, Bitcoin Cash, Litecoin, Dogecoin, Dash, Zcash)
• Works with transactions signed by @cryptoapis-io/mcp-signer or any external signer

Prerequisites

• Node.js 18+
• Crypto APIs account and API key (sign up | get API key)

Installation

npm install @cryptoapis-io/mcp-broadcast

Or install all Crypto APIs MCP servers: npm install @cryptoapis-io/mcp

Usage

# Run with API key
npx @cryptoapis-io/mcp-broadcast --api-key YOUR_API_KEY

# Or use environment variable
export CRYPTOAPIS_API_KEY=YOUR_API_KEY
npx @cryptoapis-io/mcp-broadcast

# HTTP transport (listens on 127.0.0.1; see "Exposing the server beyond localhost")
npx @cryptoapis-io/mcp-broadcast --transport http --port 3000 --api-key YOUR_API_KEY

Claude Desktop

Add to your Claude Desktop config (~/Library/Application Support/Claude/claude_desktop_config.json on macOS, %APPDATA%\Claude\claude_desktop_config.json on Windows):

{
  "mcpServers": {
    "cryptoapis-broadcast": {
      "command": "npx",
      "args": ["-y", "@cryptoapis-io/mcp-broadcast"],
      "env": {
        "CRYPTOAPIS_API_KEY": "your_api_key_here"
      }
    }
  }
}

Cursor

Add to .cursor/mcp.json (project) or ~/.cursor/mcp.json (global):

{
  "mcpServers": {
    "cryptoapis-broadcast": {
      "command": "npx",
      "args": ["-y", "@cryptoapis-io/mcp-broadcast"],
      "env": {
        "CRYPTOAPIS_API_KEY": "your_api_key_here"
      }
    }
  }
}

MCP Inspector

npx @modelcontextprotocol/inspector npx @cryptoapis-io/mcp-broadcast --api-key YOUR_API_KEY

n8n

1. Start the server in HTTP mode:

   npx @cryptoapis-io/mcp-broadcast --transport http --port 3000 --api-key YOUR_API_KEY
   

2. In your n8n workflow, add an AI Agent node
3. Under Tools, add an MCP Client Tool and set the URL to http://localhost:3000/mcp

n8n in Docker: localhost inside the container is not your machine. Start the server with --host 0.0.0.0 and MCP_AUTH_TOKEN set (see Exposing the server beyond localhost), use http://host.docker.internal:3000/mcp as the URL, and add an Authorization: Bearer <token> header to the MCP Client Tool credential.

All servers default to port 3000. Use --port to assign different ports when running multiple servers.

Available Tools

broadcast_signed_transaction

Submit a signed transaction to the blockchain.

Parameter	Description
blockchain	Target blockchain (ethereum, bitcoin, binance-smart-chain, tron, polygon, etc.)
network	Network (mainnet, testnet, sepolia, mordor, nile, amoy, fuji, etc.)
signedTransactionHex	The signed transaction hex string to broadcast

CLI Arguments

Argument	Description	Default
--api-key	Crypto APIs API key	CRYPTOAPIS_API_KEY env var
--transport	Transport type: stdio or http	stdio
--host	HTTP host (use 0.0.0.0 to accept remote connections — requires an auth token with --api-key)	127.0.0.1
--auth-token	Bearer token callers must send (Authorization: Bearer <token>); prefer the MCP_AUTH_TOKEN env var	MCP_AUTH_TOKEN env var
--allowed-hosts	Comma-separated Host header allowlist for non-loopback binds	—
--port	HTTP port	3000
--path	HTTP path	/mcp
--stateless	Enable stateless HTTP mode	false

HTTP API Key Modes

When using HTTP transport, the server supports two API key modes:

• With --api-key: The key is used for all requests. x-api-key request headers are ignored.
• Without --api-key: Each request must include an x-api-key header with a valid Crypto APIs key. This enables hosting a public server where each user provides their own key.

# Per-request key mode (multi-tenant)
npx @cryptoapis-io/mcp-broadcast --transport http --port 3000
# Clients send x-api-key header with each request

Exposing the server beyond localhost

HTTP mode listens on 127.0.0.1 by default, so only processes on the same machine can reach it. To accept connections from other machines or containers, bind explicitly and protect the port:

# Startup-key mode: callers must present the token (the server refuses to start without one)
export MCP_AUTH_TOKEN=$(openssl rand -hex 32)
npx @cryptoapis-io/mcp-broadcast --transport http --host 0.0.0.0 --port 3000 --api-key YOUR_API_KEY \
  --allowed-hosts mcp.internal.example
# Clients send: Authorization: Bearer $MCP_AUTH_TOKEN

# Per-request key mode: no startup key, every request must carry the caller's own x-api-key
npx @cryptoapis-io/mcp-broadcast --transport http --host 0.0.0.0 --port 3000

--allowed-hosts restricts the Host header (DNS rebinding protection) when not bound to loopback. Prefer MCP_AUTH_TOKEN over --auth-token: command-line arguments are visible in the process list.

Stdio transport always requires an API key at startup.

Important: API Key Required

Warning: Making requests without a valid API key — or with an incorrect one — may result in your IP being banned from the Crypto APIs ecosystem. Always ensure a valid API key is configured before starting any server.

Remote MCP Server

Crypto APIs provides an official remote MCP server with all tools available via HTTP Streamable transport at https://ai.cryptoapis.io/mcp. Pass your API key via the x-api-key header — no installation required.

License

MIT