How to choose an x402 service before your agent pays
A reusable decision framework covering capability, evidence, price, policy and one-call validation.
DIRECT ANSWER
Shortlist x402 services by capability and input/output fit, then compare source quality, current quote evidence, price and network. Inspect one unpaid 402 response, enforce a narrow spend policy and run one representative paid call. Promote the service into an autonomous workflow only after the output is useful and the failure behavior is understood.
Key takeaways
- Capability fit comes before price because the cheapest wrong answer has no value.
- Registry presence and provider-reported live status are discovery signals, not proof.
- One controlled paid call is the fastest way to test settlement and output together.
The evidence ladder
Start with an identifiable provider and source documentation. Next look for a recent automated quote check. Paid-call verification adds evidence that settlement and documented output worked once. Ongoing production trust still requires monitoring, because any endpoint can change after it is verified.
| Level | Evidence | Decision |
|---|---|---|
| Discovered | Public registry or submission | Research only |
| Documented | Provider docs and schema | Shortlist |
| Quote checked | Usable unpaid 402 requirements | Budget test |
| Paid-call verified | Settlement plus expected output | Controlled adoption |
Fit and failure questions
Ask what input is required, whether the call is read-only, what the output guarantees, how timeouts are charged and whether retries can duplicate work. A provider that documents failure semantics is easier to integrate safely than a cheaper endpoint that only advertises a happy path.
The first paid call
Use a representative public input, a dedicated wallet and a cap equal to the inspected quote. Save the requirement, response status, settlement evidence and a small output sample. If any layer differs from the documentation, report the discrepancy and keep the service out of unattended workflows.
Related directory entries
Sources and methodology
TOLL·402 distinguishes public claims, registry discovery, unpaid quote checks and settled paid-call verification. Sources below support the visible claims; presence in a registry is not treated as verification.
- TOLL·402 verification states — Directory-specific evidence definitions.
- x402 buyer quickstart — Authoritative buyer implementation.
- x402 signed offers and receipts — Current extension for signed payment artifacts.