A note from the builder
Before an agent pays, someone should check the quote.
A developer sent me his x402 endpoint this week. I caught myself asking the same questions a buying agent should ask: Is it live? Is the listed price still right? Can the agent actually call it? Does it use a rail the buyer allows?
A directory gets the agent to the endpoint. That is useful. It still does not make the buying decision.
That gap is why I built 402Signal.
The buyer sends a capability or URL and its limits. 402Signal checks the strongest candidates during that request, reads the payment terms they return now, and applies the buyer's rules. It returns one route or a specific reason to stop.
It is not a wallet. The agent keeps its keys, signing authority, seller payment, and final decision.
A successful route costs $0.003 USDC. A normal typed miss costs $0. If 402Signal cannot find something the buyer can use, that should not be the billable result.
The other piece I care about is the record. A payment receipt proves that money moved. It does not explain what the agent saw or why one route passed its rules.
For buyers that require transparency, 402Signal commits routing evidence to an append-only log. Falcon-1024 authorizes the checkpoint transaction anchored on Algorand MainNet. That makes later changes to committed history detectable.
The boundary matters: this does not make the seller payment or API response post-quantum secure. Keep the private verification record returned with the route. Private replay records can retain it, but they are not a recovery service.
There is now an optional check for the gap between finding a route and paying the seller. Ask for a bound route, then have your app compare the seller's current request with the signed terms. A changed price or recipient, a different request, or expired evidence stops the handoff to your payment code. Your wallet still validates and signs the transaction.
The immediate receipt uses the log's Ed25519 signature; the cumulative Falcon anchor comes later. This checks observed terms, not the quality of what the seller delivers. The integration guide covers the supported requests and limits.
If you are building an x402 buyer, try it with a real request. I want to hear where it stops, where the evidence is thin, and what you would need before letting an agent use it repeatedly.
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