{"uid":"cap_4-DYj77H_zBiAYAcnNXrQ","slug":"foundry-x402-preflight-checker-e15c4ee7","name":"Foundry x402 Preflight Checker","description":"x402 preflight: checks a paid x402 endpoint before a payment is signed. Probes it unpaid, parses the v1 body or v2 PAYMENT-REQUIRED header, lints every accepts[] option (network, canonical USDC, EIP-712 domain name/version that signatures verify against, EIP-55 payTo, zero payTo, amount, timeout, testnet, resource host) and returns ok/warn/block with reasons. Input: URL, optionally 'POST <url>'. Deterministic, no LLM.","url":"https://minty-sprout.onrender.com/v1/x402-preflight?utm_source=zero.xyz","method":"POST","headers":{},"bodySchema":{"type":"object","properties":{"input":{"type":"string","maxLength":8000,"description":"URL of a paid x402 endpoint, optionally prefixed with GET or POST, e.g. \"POST https://api.example.com/v1/x\""}}},"responseSchema":{"type":"json","example":{"url":"https://x402-preflight.nextill-pos.workers.dev/v1/preflight","issues":[],"method":"GET","status":402,"options":[{"issues":[],"pay_to":"0xB3cDDccEe6B150c8efFD55B961afc0Ecefe7f247","scheme":"exact","network":"eip155:8453","verdict":"ok","price_usd":0.003,"asset_symbol":"USDC"}],"verdict":"ok","latency_ms":1001,"x402_version":2,"bazaar_extension":true}},"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.005","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.005/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.005","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.005","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_LZpdI_6wOolZUgC49cXNH","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.005","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Probes a paid x402 endpoint unpaid, parses the payment-required response, and lints every payment option for validity, returning an ok/warn/block verdict with detailed reasons.","exampleAgentPrompt":"Before my agent pays it, run a preflight check on the x402 endpoint at https://api.example.com/v1/data — tell me if the payTo address, USDC network, and EIP-712 domain all look safe, and whether it gets an ok, warn, or block verdict.","exampleUseCases":[{"title":"Vet x402 seller before first payment","prompt":"I want to start using a paid API at https://some-provider.example.com/v1/search but I've never paid it before — can you do an x402 preflight check on it and tell me if it's safe, what network it's on, and what the USDC payTo address is?"},{"title":"Debug a mis-configured x402 endpoint","prompt":"My x402 API at https://minty-sprout.onrender.com/v1/x402-preflight is returning payment-required but clients say the EIP-712 domain looks wrong — run a POST preflight check on it and list every issue you find."},{"title":"Agent autonomously screens new x402 APIs","prompt":"Before my shopping agent pays any new x402 API it discovers, I want it to preflight check the endpoint URL first and only proceed if the verdict is ok — can you check https://marketplace.example.com/v1/products right now?"}],"resultDescription":"Returns a JSON object with: the probed URL, HTTP method used, response status code, x402 version detected, overall verdict (ok/warn/block), latency in ms, a list of top-level issues, and a per-option breakdown including scheme, network, payTo address, amount in USD, asset symbol, EIP-712 validation results, and option-level issues and verdict. Also flags bazaar_extension if present.","failureModes":["Target URL is unreachable or times out — returns error with latency and no options","Target URL does not return a 402 status — verdict may be block with explanation","Malformed x402 payment-required body or header — issues listed per field","Zero or invalid payTo address detected — flagged as block-level issue","Testnet network detected when mainnet expected — flagged as warn or block","Input URL missing or malformed — returns validation error"],"whenToPreferThis":"Use this endpoint when an AI agent or developer needs to vet an x402 pay-per-call API before committing a payment signature. It is the right choice when you want deterministic, rule-based linting (no LLM hallucination risk) of all payment parameters including network, USDC contract address, EIP-712 domain, payTo address, amount, and timeout. Prefer it over manual inspection when building agent workflows that autonomously discover and pay x402 APIs and need a safety gate before signing.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-11-01T06:57:40.640Z","isFirstParty":false,"canonicalSlug":"foundry-x402-preflight-checker-e15c4ee7"}