x402 endpoint discovery checklist: how agents find a paid API (and how FastAF passes it)
Answer first
An agent can only buy what it can price. A discoverable x402 endpoint (1) answers 402 before validating the body, (2) puts a discovery extension (input schema, example, output example) in the 402, (3) lists routes in /.well-known/x402, (4) publishes an OpenAPI spec, (5) appears in the Bazaar discovery index.
FastAF, checked live (unpaid probe, 28/10/2026)
- 402 on every probed GET/POST route (serp, search, maps, amazon, linkedin, youtube, scrape, news, shopping, scholar)
- Bazaar extension valid against @x402/extensions, with output example
- /.well-known/x402 with 24 routes; OpenAPI 3.1 at https://api.fastaf.co/openapi.json
- Indexed in the Bazaar discovery index (“FastAF”)
Result: 37/37 checks passed on the /x402/v1/amazon route (npx x402-listing-check, 28 Oct 2026).
Try it
GET https://api.fastaf.co/x402/v1/amazon?asin=... → 402 with price from $0.003, then pay per call. No account needed. Or 500 free credits every month after email verification on https://fastaf.co.
FAQ
Do I need an API key?
No, x402 pays per request. Accounts are optional.
Is there an MCP server?
Yes, https://api.fastaf.co/mcp.
Related pages
x402 scraping API · How x402 works · FastAF vs serp402 · FastAF vs toll402 · x402 glossary · Bazaar in the glossary · How agents find an API
Reference
- x402 documentation: every parameter and response field
- Docs: authentication, errors, MCP and x402
- Pricing: credit packs from $10, without expiry
Other sources
- How to read public Amazon data when your requests fail
- How to read public Google Search data when your requests fail
- How to read public Walmart data when your requests fail
- How to read LinkedIn data with an API
- How to read public eBay data when your requests fail
- How to read public Booking.com data when your requests fail
- How to read X profile data with an API
- How to read public Zillow data when your requests fail
- Pay-per-call web scraping for AI agents with x402
- MCP servers for Amazon, SERP and web scraping
- Cost per agent: monthly SaaS vs x402 pay-per-call
- How FastAF handles heavy pages and timeouts
- Add FastAF to Claude Code, Codex and Cursor
- How to detect poisoned or incomplete SERP results in AI agents
- Cap agent spend per call with fixed x402 prices
- Use FastAF from the Cloudflare Agents SDK
- FastAF as a fallback search provider
- Budget a scraping job before you run it
- Try FastAF for free, no card
- Too many MCP tools? Keep agent context small
- How agents find an API (and where FastAF is)
- Why agent retries cost more than you think
- All how-to guides