@cryptoapis-io/mcp-signer

MCP server for local transaction signing across EVM, UTXO, Tron, XRP, Kaspa, Solana and Tezos. 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

Terminal

npm install @cryptoapis-io/mcp-signer

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

Usage

Terminal

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):

config.json

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

Cursor

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

config.json

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

MCP Inspector

Terminal

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 }`.

`tezos_sign`

Sign a Tezos operation for tz1 (ed25519), tz2 (secp256k1) or tz3 (P-256) keys (edsk… / spsk… / p2sk…).

Action	Description
`sign-forged-operation`	Sign the `forgedOperation` hex from `prepare_transactions_tezos`. The operation is decoded first: only reveal/transaction ops from the key's own address are signed, and the optional `expected` (`destination`, `amount` in mutez, `maxFee`) must match. Returns `{ signedOperation, operationHash, signature, … }`; broadcast `signedOperation`.

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