Crypto APIs Signer

MCP server for local transaction signing across EVM, UTXO, Tron, and XRP blockchains. No Crypto APIs HTTP calls — signing happens entirely on your machine. No API key required.

Security

• Stdio only — no HTTP transport. The server does not listen on any port.
• Private keys in tool input — each tool receives privateKey / privateKeys / secret as parameters. Keys are never read from environment variables.
• No network calls — all signing is done locally using cryptographic libraries.

Installation

npm install @cryptoapis-io/mcp-signer

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

Usage

npx @cryptoapis-io/mcp-signer

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-signer": {
      "command": "npx",
      "args": ["-y", "@cryptoapis-io/mcp-signer"]
    }
  }
}

Cursor

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

{
  "mcpServers": {
    "cryptoapis-signer": {
      "command": "npx",
      "args": ["-y", "@cryptoapis-io/mcp-signer"]
    }
  }
}

MCP Inspector

npx @modelcontextprotocol/inspector npx @cryptoapis-io/mcp-signer

Available Tools

evm_sign

Sign an EVM transaction (Ethereum, Ethereum Classic, BSC, Polygon, Avalanche (C-Chain), Arbitrum, Base, Optimism, Tron).

Action	Description
sign-from-details	Sign from structured transaction fields (to, value, gasLimit, etc.)
sign-unsigned-hex	Sign a pre-built unsigned transaction hex
sign-typed-data	Sign an EIP-712 typed-data message (the x402 gasless path — e.g. the EIP-3009 TransferWithAuthorization from the x402 buyer /authorize). Returns { signature }, not a tx.

utxo_sign

Sign a UTXO transaction (Bitcoin, Bitcoin Cash, Litecoin, Dogecoin, Dash, Zcash).

Action	Description
sign-from-details	Sign from a prepared transaction object (inputs, outputs)
sign-unsigned-hex	Sign a raw unsigned transaction hex with input descriptors

tron_sign

Sign a Tron transaction using secp256k1 (no TronWeb dependency).

Action	Description
sign-from-details	Sign from a transaction object with raw_data_hex
sign-unsigned-hex	Sign a pre-built unsigned transaction hex

xrp_sign

Sign an XRP transaction.

Action	Description
sign-from-details	Sign from structured XRP transaction fields
sign-unsigned-hex	Sign a pre-built unsigned transaction hex

kaspa_sign

Sign a Kaspa transaction using schnorr (BIP340) via kaspa-wasm. Mainnet only.

Action	Description
sign-from-details	Sign a prepared Kaspa transaction (from the prepare-transaction API)

svm_sign

Partial-sign a Solana (SVM) x402 payment transaction — the buyer's source-authority signature only (the facilitator's feePayer slot stays unsigned, signed at settle).

Action	Description
partial-sign	Deserialize the base64 unsigned TransferChecked tx from the x402 buyer /authorize (scheme svm-transaction), add the buyer signature, re-serialize to base64. Returns { transaction }.

Most tools return signedTransactionHex — ready to broadcast with @cryptoapis-io/mcp-broadcast. The x402 paths return { signature } (EVM typed-data) or { transaction } (SVM) instead.

Dependencies

Package	Purpose
ethers	EVM transaction signing
bitcoinjs-lib + ecpair + tiny-secp256k1	UTXO transaction signing
elliptic	Tron transaction signing (secp256k1)
xrpl	XRP transaction signing

License

MIT