Check an x402 payment challenge before your agent pays: network, USDC, amount, payTo, facilitator.
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Check an x402 payment challenge BEFORE your agent pays (0.002 USDC per check via x402; free trial 1024 checks/IP/UTC day). Give an endpoint URL (fetched unpaid, never paid) or paste a 402 challenge. Validates x402 version, scheme, network (CAIP-2, testnet flag), canonical USDC asset, amount sanity, payTo format/EIP-55 checksum/zero address, EIP-712 domain, payment window, facilitator reachability and scheme/network support, optional maxPriceUsd / expectPayTo / expectNetwork policy, and PayAI Bazaar listing match. Returns per-check pass/warn/fail and a verdict: looks_ok, review or do_not_pay. Informational; invalid input and failed checks are not charged.
x402 endpoint URL to probe (public http/https). Fetched unpaid; never paid.
HTTP method used to probe url
Alternative to url: the 402 challenge itself (JSON body, or the base64 PAYMENT-REQUIRED header value). Takes precedence over url.
Policy: fail options whose payTo differs from this address
Facilitator base URL to test (https). Default: PayAI (mainnet) / x402.org (testnet).
Policy: fail options priced above this many USD (USDC)
Policy: fail options not on this network (CAIP-2, e.g. eip155:8453)
Compare live terms with the PayAI Bazaar listing (url mode)
Pick your client. Values in capitals, like YOUR_TOKEN, are yours to fill in.
Run in a terminal
claude mcp add --transport http precheck https://x402-precheck.w0arvg81zlgf.workers.dev/mcp
Check an x402 payment challenge BEFORE your agent pays (0.002 USDC per check via x402; free trial 1024 checks/IP/UTC day). Give an endpoint URL (fetched unpaid, never paid) or paste a 402 challenge. Validates x402 version, scheme, network (CAIP-2, testnet flag), canonical USDC asset, amount sanity, payTo format/EIP-55 checksum/zero address, EIP-712 domain, payment window, facilitator reachability and scheme/network support, optional maxPriceUsd / expectPayTo / expectNetwork policy, and PayAI Bazaar listing match. Returns per-check pass/warn/fail and a verdict: looks_ok, review or do_not_pay. Informational; invalid input and failed checks are not charged.
| Argument | Type | Description |
|---|---|---|
| url | string | x402 endpoint URL to probe (public http/https). Fetched unpaid; never paid. |
| method | string | HTTP method used to probe url |
| challenge | string | object | Alternative to url: the 402 challenge itself (JSON body, or the base64 PAYMENT-REQUIRED header value). Takes precedence over url. |
| expectPayTo | string | Policy: fail options whose payTo differs from this address |
| facilitator | string | Facilitator base URL to test (https). Default: PayAI (mainnet) / x402.org (testnet). |
| maxPriceUsd | string | Policy: fail options priced above this many USD (USDC) |
| expectNetwork | string | Policy: fail options not on this network (CAIP-2, e.g. eip155:8453) |
| compareDirectory | string | Compare live terms with the PayAI Bazaar listing (url mode) |
{
"type": "object",
"properties": {
"url": {
"type": "string",
"description": "x402 endpoint URL to probe (public http/https). Fetched unpaid; never paid."
},
"method": {
"enum": [
"GET",
"POST"
],
"type": "string",
"default": "GET",
"description": "HTTP method used to probe url"
},
"challenge": {
"type": [
"string",
"object"
],
"description": "Alternative to url: the 402 challenge itself (JSON body, or the base64 PAYMENT-REQUIRED header value). Takes precedence over url."
},
"expectPayTo": {
"type": "string",
"description": "Policy: fail options whose payTo differs from this address"
},
"facilitator": {
"type": "string",
"description": "Facilitator base URL to test (https). Default: PayAI (mainnet) / x402.org (testnet)."
},
"maxPriceUsd": {
"type": "string",
"description": "Policy: fail options priced above this many USD (USDC)"
},
"expectNetwork": {
"type": "string",
"description": "Policy: fail options not on this network (CAIP-2, e.g. eip155:8453)"
},
"compareDirectory": {
"enum": [
"true",
"false"
],
"type": "string",
"default": "true",
"description": "Compare live terms with the PayAI Bazaar listing (url mode)"
}
}
}We read every tool's name, description and inputs the way the model will, looking for instructions hidden from you. A clean result means no warning signs, not a guarantee. Scanned Nov 10, 2026.