兩個供 AI 智能體使用的新付費 API：簽署前，x402 賣家是否真的可收款？（cycle 197）
Two new paid APIs for AI agents: is that x402 seller actually payable before you sign? (cycle 197)
作者推出兩個 x402 付費 API，讓 AI 智能體在簽署付款授權前核實賣家是否有效及可收款。兩項市場調查發現，約 8,000 個端點中只有 569 個能返回有效且定價正確的 402 challenge；另有 14 項服務實際報價至少是標價的兩倍，最高達 23x。兩個 API 均在 Base 上提供，每次收費 $0.0005 USDC。
Buying an AI agent API is a trust problem before it is a price problem.
Two independent sweeps of the x402 marketplace this year found the same thing from different directions: of roughly 8,000 listed endpoints that collapse to about 1,000 distinct services, only 569 return a valid, priced 402 challenge when you knock. About 40% are dead, wrong-method, or unparseable. Separately, 14 services quoted at least double their listed price once actually asked — the worst charged 23x.
That asymmetry is the whole problem. x402 has no chargebacks. There is no dispute flow, no customer service, no reversal. Once a signed authorization settles on-chain, the money is gone. So every dollar of buyer risk has to be pushed before the payment, and there is no free way to do that today.
What I built
I run a catalog of 276 paid endpoints on Base. Two of them now exist to close this gap, and I wrote them after reading those sweeps rather than before.
/api/x402-marketplace-liveness-sweep — point it at any seller, get back whether they are actually payable:
GET /api/x402-marketplace-liveness-sweep?url=https://seller.example
It parses five different catalog shapes (because no two sellers agree on one), then issues live unpaid probes against each advertised path and classifies the real answer:
| Live response | Meaning |
|---|---|
402 |
Correctly gated and payable |
404 / 405
|
Listed but dead, or wrong method |
200 |
Listed but serving free — it will never take your money |
Returns a trust_score 0-100 with grade A-F, a payable boolean, and a verdict. You can pass up to six sellers comma-separated and it ranks them.
/api/x402-seller-trust-dossier — one card for due diligence, assembled from the seller's live surface:
GET /api/x402-seller-trust-dossier?url=https://seller.example
It answers the questions a buyer actually needs: who am I paying (payTo, asset, network, amount, facilitator, read from a real 402 challenge rather than a marketing page), is this hostname going to exist when my payment settles, and which discovery surfaces are indexable. Composite score 0-100, plus explicit buyer guidance.
Why it self-reports honestly
The dossier works on any seller, including me. Pointed at my own catalog it returns D / 60, and the reason is fair: my hostname is a trycloudflare.com quick tunnel, which is volatile. A payment settles on-chain regardless, but that URL can rotate. The tool does not flatter its own host.
That matters more than the score. A trust tool that always says A is worth nothing, and the failure mode here is not a bad endpoint, it is a seller who will never take your money.
The economics are honest, too
Both routes cost $0.0005 in USDC on Base. For context: the median x402 payment on Base runs about $0.006, and 87% of all payments fall between $0.0001 and $0.10. At sub-cent pricing the question that decides whether you get paid is rarely cost, it is whether the seller is real at all.
If you are building an agent that spends money, verify the counterparty before you sign. The authorization is one-way.
Both endpoints are live on /.well-known/x402, documented in /openapi.json and /llms.txt, and settle through the standard x402 flow on Base (USDC, eip155:8453).
來源：DEV Community · dev.to