Lingua Detective x402 MCP

MCP server exposing Lingua Detective's paid APIs with per-call x402 payments (USDC on Solana, gas sponsored): no account, no API key, no subscription. An AI agent calls the tool, pays a few cents, and receives the result.

Tools (4)

Related MCP server: farebox-mcp

Payment modes

The server reads its configuration from the environment. Two modes (in priority order):

1. Prepaid credit — X402_CREDIT_TOKEN: an opaque token obtained via a top-up (credit_topup or bundle_check). Each call debits the credit without a Solana transaction. Ideal for high volume.

2. Payer wallet — X402_PAYER_KEY_B64: a Solana private key (64 bytes, base64) of a wallet funded in USDC (no SOL required: gas is sponsored by the facilitator). Each call settles its x402 transaction automatically.

With neither, the tools return the decoded 402 challenge (amount, payTo address, network) so the agent understands what is being requested.

Environment variables

Installation

Claude Desktop

{
  "mcpServers": {
    "linguadetective": {
      "command": "npx",
      "args": ["-y", "lingua-x402-mcp"],
      "env": {
        "X402_PAYER_KEY_B64": "<your base64 private key>",
        "X402_TRUSTED_PAYTO": "H3NuGHu9mpGgscj2DWtrs699PWdovPUicy2N9dDaYLTk"
      }
    }
  }
}

Cursor / other stdio clients

Add the same command: npx, args: ["-y", "lingua-x402-mcp"] entry with your env.

Local

git clone https://github.com/maximethemens-code/lingua-x402-mcp && cd lingua-x402-mcp && npm install
X402_PAYER_KEY_B64=... npm start   # npm start = node src/index.js

Example call

detect_langue { text: "Bonjour tout le monde, ceci est une phrase en français." }
→ { "langues": [ { "code": "fra", "nom": "français", ... } ], ... }   ($0.002 USDC debited)

Security

• X402_PAYER_KEY_B64 is never sent to the server: it is only used to sign the transaction locally.

• X402_TRUSTED_PAYTO is strongly recommended: it prevents the wallet from paying an unexpected recipient (e.g. if X402_BASE_URL points to a malicious server).

• The payment wallet must be distinct from the receiving wallet (payTo).

Known limitations

• Detection is offline (the franc library, 186 languages, ISO 639-3 codes): no network call, but a text that is too short (< 10 characters) returns an error.

• Real on-chain settlement (verify/settle via Dexter) is only exercised with a wallet actually funded in USDC.