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Agent Endpoint Preflight (x402 Interoperability Checker)
x402
Agent Endpoint Preflight (x402 Interoperability Checker) is a paid API for AI agents from api.x402preflight.com, paid per call via x402, $0.05/call, status unknown (last checked 2026-09-15).
Checks a public endpoint's x402 payment challenge, network/asset/amount terms, origin binding, canonical V2 structure, and common integration failures without actually making a payment.
Price / call$0.05
Success—
StatusUnknown
How this service works
Read-only x402 endpoint interoperability preflight. Checks a public endpoint's payment challenge, network/asset/amount terms, origin binding, canonical V2 structure, and common integration failures without making a payment. Payment purchases one bounded assessment attempt. PASS DOES NOT MEAN SAFE. WARN, REJECT, NOT_X402, TARGET_UNREACHABLE, and TIMEOUT may be valid paid results.
Output
A JSON object containing a verdict string (PASS, WARN, REJECT, NOT_X402, TARGET_UNREACHABLE, or TIMEOUT), a canonical boolean, a reachable boolean, the observed HTTP status, an observedAt timestamp, an array of reasonCodes, structured paymentTerms (asset contract address, payTo address, amount, scheme, network, maxTimeoutSeconds), a challengeHash, originBinding validity, a redirectChain array, schemaFindings array, protocolVersion integer, and a securityFindings array.
Example use cases
Pre-integration x402 compliance audit
“Before I wire up my agent to pay https://api.examplepartner.com/data, can you run a preflight check on it and tell me whether it passes x402 canonical V2 validation and what asset and amount it's asking for?”
Debugging a 402 endpoint that keeps rejecting payments
“My payments to https://api.provider.io/v2/stream keep failing — can you do an x402 preflight on it and tell me the verdict and any reason codes or schema findings that might explain why the integration is broken?”
Checking origin binding before deploying an agent
“I'm about to deploy an agent that will call https://api.newvendor.com/agent-feed — can you preflight its x402 endpoint and confirm whether the origin binding is valid and the network is eip155:8453 with USDC?”
Technical details
Endpoint
POSThttps://api.x402preflight.com/v1/preflightWhen to prefer
Use this endpoint when you need a read-only, non-paying diagnostic of any public x402 endpoint — especially before integrating an agent payment flow, debugging 402 negotiation failures, auditing canonical V2 structure compliance, or verifying payment terms (asset, network, amount) without committing real USDC. Prefer this over manually parsing 402 headers or attempting a live payment when the correctness of the remote endpoint is uncertain.
Side effects
- TARGET_UNREACHABLE verdict when the target URL is offline or DNS fails
- TIMEOUT verdict when the target endpoint does not respond within the allowed window
- NOT_X402 verdict when the target does not return an HTTP 402 response at all
- REJECT verdict when the endpoint fails critical x402 structural requirements
- Payment of $0.05 USDC is consumed even if the result is WARN, REJECT, NOT_X402, TARGET_UNREACHABLE, or TIMEOUT — PASS is not guaranteed
- Malformed or unexpected paymentTerms fields if the target uses a non-standard x402 implementation
Output
Schema · Response
{
"type": "json",
"example": {
"verdict": "WARN",
"canonical": false,
"reachable": true,
"httpStatus": 402,
"observedAt": "2026-01-01T00:00:00.000Z",
"reasonCodes": [
"NONCANONICAL_RESOURCE"
],
"paymentTerms": {
"asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
"payTo": "0x0000000000000000000000000000000000000000",
"amount": "50000",
"scheme": "exact",
"network": "eip155:8453",
"maxTimeoutSeconds": 300
},
"challengeHash": "sha256:example",
"originBinding": {
"valid": true
},
"redirectChain": [],
"schemaFindings": [
"NONCANONICAL_RESOURCE"
],
"protocolVersion": 2,
"securityFindings": []
}
}Tags
x402
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