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x402 Payment Preflight Shortlist
x402
x402 Payment Preflight Shortlist is a paid API for AI agents from email-preflight-api.vercel.app, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-15).
Searches the Coinbase CDP Bazaar for x402-payment-gated endpoints matching a described need, probes live candidates for valid 402 challenges, and recommends the best passing candidate with full payment details.
Price / call$0.005
Success—
StatusUnknown
How this service works
Pre-action x402 payment checks and deterministic email HTML validation for AI agents.
Output
A JSON object containing: a recommended endpoint with full x402 payment fields (payTo address, asset contract, atomic amount, USD amount, network, scheme), the live check result (HTTP status, payment match, resource match), search metadata (provider, result count, search method), privacy assurances (no credential forwarding, no body forwarding), probe statistics (candidates considered, probed count, deadline), and a list of alternates if the top pick fails. Also includes limitations disclaiming merchant identity and settlement guarantees.
Example use cases
Verify cheapest live weather API
“I need current weather data and want to pay via x402 on Base. Can you search for live endpoints that do weather lookups, cost under a cent, and have passed a real 402 probe? Give me the best one with its payment address and amount.”
Discover live translation service on Base
“Find me a working x402 API for text translation on eip155:8453 — I want to confirm it's actually live and responding with a proper 402 before I send any payment. Cap the price at $0.02.”
Preflight before autonomous agent purchase
“My agent is about to pay for a geolocation lookup using x402 on Base network, max $0.005. Before it pays, can you shortlist the best candidate endpoints, probe them live, and tell me which one passes so we send money to a real working service?”
Technical details
Endpoint
POSThttps://email-preflight-api.vercel.app/api/x402-shortlist?utm_source=zero.xyzWhen to prefer
Use this endpoint when an AI agent needs to autonomously discover and pay for an unknown x402-gated API without hard-coding a specific URL — especially when you want deterministic liveness verification (real HTTP 402 probe) layered on top of semantic search ranking, before committing any on-chain payment. Prefer this over querying the Coinbase Bazaar directly when you also need live endpoint health confirmation and structured payment parameters ready for immediate use.
Side effects
- No candidates found — Bazaar returns zero results for the described need; ok:false with empty recommendation
- All probed candidates fail live check — none return a valid 402 with matching payment details; status:partial or failed
- Probe deadline exceeded — probeDeadlineMs elapsed before all candidates could be checked; partial results returned
- Network mismatch — requested network has no indexed x402 endpoints in Bazaar
- Price ceiling too low — all discovered endpoints exceed maxPriceUsd; no recommendation made
- Bazaar search unavailable — upstream CDP search endpoint unreachable; service error returned
Output
Schema · Response
{
"type": "json",
"example": {
"ok": true,
"live": true,
"checks": {
"probeLimit": 3,
"probedCount": 3,
"candidateLimit": 6,
"probeDeadlineMs": 3500,
"selectionPolicy": "Preserve Coinbase Bazaar search rank; recommend the first candidate that passes every local deterministic live check."
},
"search": {
"status": "completed",
"endpoint": "https://api.cdp.coinbase.com/platform/v2/x402/discovery/search",
"provider": "Coinbase CDP Bazaar",
"resultCount": 4,
"searchMethod": "vector",
"rankingNotice": "Search rank is supplied by Coinbase Bazaar from retrieval relevance and service-quality signals; those signals are not independently verified here.",
"partialResults": true,
"consideredCount": 4
},
"status": "partial",
"privacy": {
"retained": false,
"targetPaymentsMade": false,
"callerBodyForwarded": false,
"credentialsForwarded": false,
"callerHeadersForwarded": false,
"rawUpstreamBodiesReturned": false
},
"request": {
"need": "current weather for a city",
"method": "GET",
"network": "eip155:8453",
"maxPriceUsd": 0.01
},
"service": "x402-purchase-shortlist",
"version": "2026-07-31",
"alternates": [],
"limitations": [
"Coinbase Bazaar supplies search rank; this service adds deterministic live checks, not an independent quality score.",
"A recommendation does not establish merchant identity, settlement success, endpoint quality, safety, endorsement, or future behavior."
],
"recommendation": {
"rank": 1,
"price": {
"asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
"payTo": "0x1111111111111111111111111111111111111111",
"scheme": "exact",
"network": "eip155:8453",
"amountUsd": "0.005",
"amountAtomic": "5000",
"amountUsdBasis": "USDC (6 decimals)"
},
"method": "GET",
"request": {
"url": "https://weather.example/api/current?city=Toronto",
"query": {
"city": "Toronto"
},
"method": "GET",
"headers": {
"Accept": "application/json"
}
},
"resource": "https://weather.example/api/current?city=Toronto",
"liveCheck": {
"status": "passed",
"httpStatus": 402,
"paymentMatched": true,
"resourceMatched": true,
"bazaarInvocationMetadataPresent": true
},
"searchRank": 2,
"description": "Current weather observations for a requested city.",
"bazaarLastUpdated": "2026-07-31T12:00:00Z",
"declaredServiceName": "Example Weather API"
},
"disqualifications": [
{
"code": "bazaar_payment_live_mismatch",
"stage": "probe",
"message": "Bazaar amount, network, asset, or payee metadata is stale or inconsistent with the live challenge.",
"resource": "https://stale.example/api/weather",
"searchRank": 1
}
]
}
}Tags
x402
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