# Agent Preflight APIs Pre-action x402 payment checks and deterministic email HTML validation for AI agents. - Paid endpoint: POST https://email-preflight-api.vercel.app/api/x402-shortlist - Price: USD 0.005 in USDC on Base through x402 v2 - Free static shortlist sample: GET https://email-preflight-api.vercel.app/api/x402-shortlist/sample - Paid endpoint: POST https://email-preflight-api.vercel.app/api/preflight - Price: USD 0.01 in USDC on Base through x402 v2 - Paid endpoint: POST https://email-preflight-api.vercel.app/api/x402-preflight - Price: USD 0.003 in USDC on Base through x402 v2 - Free x402 response sample: GET https://email-preflight-api.vercel.app/api/x402-preflight/sample - Agent skill: https://email-preflight-api.vercel.app/SKILL.md - OpenAPI: https://email-preflight-api.vercel.app/openapi.json - x402 descriptor: https://email-preflight-api.vercel.app/.well-known/x402 - Health: https://email-preflight-api.vercel.app/api/health x402 Purchase Shortlist input JSON: {"need":"current weather for a city","maxPriceUsd":0.01,"network":"eip155:8453","method":"GET"} It searches only the official public Coinbase Bazaar discovery host with a small result limit, preserves Bazaar's relevance/quality order as searchRank, and probes at most three candidates in parallel through the hardened unpaid probe. It rejects unsafe targets, filters, challenge/resource/payment drift, and incomplete invocation metadata. It returns one recommendation, alternates, disqualifications, and request skeletons. Partial search and timeout results are labeled. It makes no target payment and does not establish merchant identity, settlement success, endpoint quality, safety, endorsement, or future behavior. Input JSON: {"html":"..."} The response reports Gmail clipping risk, source-size contributors, missing image alt attributes, unsafe or placeholder links, embedded data images, and whether active source contains an unsubscribe reference. Do not submit subscriber lists or other personal data. Use x402 Endpoint Preflight immediately before paying an unfamiliar API. It sends one unpaid GET, HEAD, or POST request to a public HTTPS target. It never sends payment, authorization, cookie, credential, or caller-supplied headers; refuses redirects; and returns deterministic checks of the x402 v2 challenge and optional Bazaar metadata. It does not verify settlement, merchant identity, endpoint quality, or future behavior. Input JSON: {"url":"https://merchant.example/api/resource","method":"POST","expected":{"network":"eip155:8453","maxAmountUsd":0.01}} POST probes always send the fixed JSON object {} to the target; callers cannot supply target request content.