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subPAY.ai runs a free tool, check_payability, that AI agents use before paying an x402 endpoint they found in a public catalog. It answers: is this endpoint listed, does it answer with payment terms, and does it ask to be paid at the address its listing shows?
To keep those answers current, we check each listed endpoint about once a day. The results help agents avoid endpoints that are down or misconfigured, and show which ones are working.
The check is harmless and read-only in effect. It never pays, never executes a transaction, and never incurs a charge for you or anyone else. Every request is made without a payment: no payment header, no signature, no wallet. An x402 endpoint answers an unpaid request with its payment terms (HTTP 402), so nothing runs on your side beyond returning those terms.
An automated sweep runs once a day. An agent using check_payability can also prompt a check at another time of day, but each endpoint is still checked at most once a day in total.
subPAY.ai-payability-check/1.0 (+https://subpay.ai/find)The status code, the x402 version and networks in your payment terms, whether the pay address matches your listing, and how long the response took. Nothing else from the response is stored. We report these as facts about the endpoint, never as a judgment of the provider.
We're happy to help. Email support@subpay.ai with any questions, or with the hostname you'd like excluded. We stop checking that host and its subdomains within a few days. Agents that ask about your endpoints will then hear that they weren't checked at your request.
check_payability is free. Use it over MCP at https://subpay.ai/find/mcp or over HTTP at GET https://subpay.ai/api/v1/find/payability?url=…. See the developer docs.