x402 seller payability check

Buy one call from an x402 seller endpoint right now and report exactly what happened: the unpaid call's status, the 402 decoded (accepts, chains, payTo, asset, price), whether the accept's EIP-712 domain name matches the token it names (the defect that silently makes a whole catalog unpayable), whether a stock client's signed payment was accepted, the settlement receipt and transaction, a slice of the response body, and the time each leg took. Send POST /api/seller-payability with the required field url and pay $0.10 per call over x402 with USDC on an EVM chain. It returns a JSON object with url, method, checkedAt, payable, unpaidCall and 5 more.

Ends in plain-English flags, never a score. This is the live counterpart to seller-dossier, which reports what we already know: this one spends real USDC from our own wallet to find out. Point it at your own endpoint before you launch, or at a seller you are about to route money to. Up to $0.02 of the seller's price per check.

Category: x402 seller intelligence · Tags: x402 seller payability payment 402 check verify settlement · Also found as: payability-check can-i-pay-this seller-payment-check x402-payability

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/seller-payability \
  -H "Content-Type: application/json" \
  -d '{"url":"https://agent402.tools/api/hash","method":"POST","body":{"text":"hello"}}'

Without payment this returns HTTP 402 Payment Required with the exact price for seller-payability; any x402 v2 or MPP client pays it and retries.

Example response

{
  "url": "https://agent402.tools/api/hash",
  "method": "POST",
  "checkedAt": "2026-09-11T02:00:00.000Z",
  "payable": true,
  "unpaidCall": {
    "status": 402,
    "contentType": "application/json",
    "error": null,
    "ms": 180,
    "bodySlice": "{}"
  },
  "challenge": {
    "readable": true,
    "networks": [
      "eip155:8453"
    ],
    "priceUsd": 0.01,
    "payTo": "0x…",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "pricedFrom": "eip155:8453",
    "accepts": []
  },
  "domainFindings": [
    {
      "network": "eip155:8453",
      "verdict": "matches",
      "advertisedName": "USD Coin",
      "expectedName": "USD Coin",
      "chain": "Base"
    }
  ],
  "payment": {
    "attempted": true,
    "status": 200,
    "settled": true,
    "error": null,
    "ms": 2400,
    "receipt": {
      "network": "eip155:8453",
      "payer": "0x…",
      "transaction": "0x…",
      "success": true
    }
  },
  "responseSlice": "{\"summary\":\"…\"}",
  "flags": [
    "a stock buyer can pay this endpoint and get a result: nothing to fix"
  ]
}

From an MCP client

catalog.call {
  "slug": "seller-payability",
  "params": {
    "url": "https://agent402.tools/api/hash",
    "method": "POST",
    "body": {
      "text": "hello"
    }
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for seller-payability; the stdio package pays it from a wallet or from AGENT402_CREDITS_KEY. Local install: npx -y agent402-mcp.

Errors and behavior

• url is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement is cancelled when the tool fails.
• Wallet-only: this tool reaches the network or stored state, so it has no proof-of-work tier. A prepaid card-credits key issued earlier (Authorization: Bearer a402_...) also pays it.
• Long-running: payment settles after the work finishes, so only EVM exact payments are offered.
• A GET or HEAD to /api/seller-payability returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB is not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/seller-payability", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "url": "https://agent402.tools/api/hash",
    "method": "POST",
    "body": {
      "text": "hello"
    }
  }),
});

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