x402-trust-mcp

An MCP server that lets your agent check the trust & reliability of x402 endpoints before paying them.

Backed by x402.fuchss.app, which monitors the entire x402 ecosystem on Base 24/7: uptime probes, 402-envelope spec compliance, advertised-price history, and real on-chain USDC settlement volume per endpoint.

Why

Agents increasingly pay x402 endpoints autonomously. But ~⅔ of listed x402 endpoints are unreachable and ~⅓ of the reachable ones serve non-compliant payment envelopes. Before your agent sends USDC to an unknown endpoint, ask: is it alive, compliant, and does anyone actually pay it?

Related MCP server: Thoughtproof-mcp

Tools

Paid tools cost a few tenths of a cent, charged over x402 (USDC on Base). If you set X402_PRIVATE_KEY, the server auto-pays within your X402_MAX_USD limit; otherwise it returns the price quote for your host to pay.

x402_trust_score result

A single call returns everything an agent needs to decide whether and at what price to use an endpoint — no second round-trip, no raw-unit guessing:

Everything is computed deterministically (no LLM) from continuous on-chain and probe observation, so the breakdown is fully auditable.

x402 V2 Payment Flow

This MCP server uses the canonical x402 V2 payment flow:

1. 402 + PAYMENT-REQUIRED — The server responds with HTTP 402 and a base64-encoded PAYMENT-REQUIRED header containing the payment requirements (accepts, network, asset, amount, payTo).

2. Sign + retry with PAYMENT-SIGNATURE — The MCP client signs an EIP-3009 transferWithAuthorization for the selected accept and re-POSTs with the PAYMENT-SIGNATURE header (base64-encoded payment payload).

3. Settlement + PAYMENT-RESPONSE — The server settles the payment and responds with the data plus a PAYMENT-RESPONSE header.

Legacy X-PAYMENT / X-PAYMENT-RESPONSE headers are accepted as a fallback during the V1→V2 transition period but are not the default.

Accept selection: When a 402 response offers multiple accepts (e.g. Solana

• Base USDC), the client selects the best compatible one (canonical USDC on an allow-listed chain) rather than blindly taking the first accept.

Install

Add to your MCP client config (e.g. Claude Desktop claude_desktop_config.json):

{
  "mcpServers": {
    "x402-trust": {
      "command": "npx",
      "args": ["-y", "x402-trust-mcp"]
    }
  }
}

To enable autonomous payment for the paid tools, add a funded Base USDC wallet:

{
  "mcpServers": {
    "x402-trust": {
      "command": "npx",
      "args": ["-y", "x402-trust-mcp"],
      "env": {
        "X402_PRIVATE_KEY": "0xYOUR_BASE_WALLET_KEY",
        "X402_MAX_USD": "0.05"
      }
    }
  }
}

Configuration (env vars)

The free tools work with no configuration at all.

Security

X402_PRIVATE_KEY is a hot wallet — fund it with only what you're willing to spend on trust lookups. The key never leaves your machine; it signs EIP-3009 payment authorizations locally.

Policy checks enforced before signing:

• Chain allow-list (Base mainnet by default)

• Canonical USDC contract verification (no arbitrary tokens)

• Optional payTo allow-list

• Per-call spend ceiling (X402_MAX_USD)

• Cumulative spend cap (X402_MAX_TOTAL_USD)

• Call-count cap (X402_MAX_CALLS)

License

MIT