exhibit402-mcp

MCP server for exhibit402, a live x402-paid web-evidence service. It lets an agent pay USDC on Base to permanently certify what a public URL serves right now, and to re-verify existing certificates.

How a capture works: two independent observers on different networks capture the URL at the same frozen instant. Byte-identical captures get tier CERTIFIED. Differing captures get tier WITNESSED, with a pixel agreement percentage and a diff map. Either way the evidence (screenshot plus a signed manifest) is stored permanently on Arweave, an RFC 3161 timestamp token is included, and an ERC-721 certificate is minted on Base to the wallet that paid.

Machine-readable service docs: /llms.txt and /openapi.json.

Tools

If certify_url hits its polling timeout, it still returns the claim_url. Claim tickets are durable and free to read: fetch the claim URL later with a plain GET to collect the finished certificate. You are not charged twice.

Refund policy (disclosed by the service): rejected captures (oversize, unreachable page, content screen) refund automatically minus a $0.10 fee; service faults refund in full. WITNESSED is a deliverable, not a failure, and is not refunded.

Related MCP server: VERITY

Setup

You need one environment variable:

• EXHIBIT402_WALLET_KEY: an EVM private key (hex) for a wallet that holds USDC on Base (chain id 8453). The wallet needs no ETH; x402 settles via EIP-3009 and the facilitator pays gas. The key stays in your process environment and is never logged.

Without the key the server still starts and lists its tools, and every call returns a clear setup error instead of failing silently.

Claude Code (one line)

claude mcp add exhibit402 --env EXHIBIT402_WALLET_KEY=0xYOUR_KEY -- npx -y exhibit402-mcp

Claude Desktop

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "exhibit402": {
      "command": "npx",
      "args": ["-y", "exhibit402-mcp"],
      "env": { "EXHIBIT402_WALLET_KEY": "0xYOUR_KEY" }
    }
  }
}

Cursor

Add to .cursor/mcp.json:

{
  "mcpServers": {
    "exhibit402": {
      "command": "npx",
      "args": ["-y", "exhibit402-mcp"],
      "env": { "EXHIBIT402_WALLET_KEY": "0xYOUR_KEY" }
    }
  }
}

Pricing summary

All payments are x402 (USDC on Base, eip155:8453). Payment settles before the capture starts; polling the claim ticket is free.

Notes for operators

• EXHIBIT402_URL overrides the service base URL (default https://exhibit402.dylan-caponi.workers.dev). You will not normally need it.

• Fulfillment is normally 30 to 120 seconds, up to about 5 minutes with a cold observer or a retry round.

• A verified: false verdict from verify_certificate is a delivered result and is charged. Malformed ids, unknown ids, and gateway outages are not charged.

• The service refuses private and internal addresses before payment.

License

MIT