The three-step contract

Step 1 — free preview. Every paid path has a free twin that returns a truncated sample of the real output, so a buyer can verify the shape before any wallet action:

GET https://sigtap-outreach-api.sigtap.workers.dev/preview/tools/uuid?version=v7

{"preview":true,"route":"/tools/uuid","limit":5,"version":"v7",
 "ids":["7fa227ee-01a0-7054-af68-ad9e29d5f1f8",
        "7fa227ee-01a0-795a-8d78-3ce4cf3243dc"],
 "truncated":false,"paid_unlocks":"up to 100 ids per call"}

Step 2 — the 402 challenge. Calling the paid path without payment returns 402 with a base64 payment-required response header (x402 v2: exact scheme, network eip155:8453, PayAI facilitator, payTo inside the challenge). The response also carries x-free-preview pointing back at the free sample.

Step 3 — pay and retry the SAME GET. Sign an EIP-3009 USDC transfer for the asked amount, attach it as the X-PAYMENT header, replay the request; you get 200 plus a payment-response header with the on-chain settlement.

Pay in one call (copy-paste)

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPaymentFromConfig } from "@x402/fetch";
import { ExactEvmScheme } from "@x402/evm";
import { privateKeyToAccount } from "viem/accounts";

const fetchWithPayment = wrapFetchWithPaymentFromConfig(fetch, {
  schemes: [{ network: "eip155:8453", client: new ExactEvmScheme(privateKeyToAccount(PRIVATE_KEY)) }]
});

const res = await fetchWithPayment("https://sigtap-outreach-api.sigtap.workers.dev/tools/uuid?count=3&version=v7"); // $0.0005
console.log(res.status, await res.json()); // 200 { ids: [...] }

The client reads the 402, signs, retries — one round-trip of your code, no keys/accounts (the wallet IS the account).

Python

pip install sigtap-agent-tools

from sigtap_agent_tools import client
print(client.preview("tools/hash", text="hello"))    # 200 free sample
print(client.challenge("tools/hash", text="hello"))  # decoded 402 challenge
# client.paid_call(...) settles via a funded key

MCP (Claude Code / Cursor / any MCP client)

{
  "mcpServers": {
    "sigtap-agent-tools": {
      "type": "http",
      "url": "https://sigtap-mcp.sigtap.workers.dev/mcp"
    }
  }
}

First unpaid tools/call returns a JSON-RPC error carrying the same x402 challenge; pay once and the tool works for the session.

What sells at impulse prices

Verified prices from the live catalog (/llms.txt, /openapi.json):

Notes for builders

• Send a browser-like User-Agent: bare python-urllib gets Cloudflare 1010 from many workers.dev origins (ours included).
• The 402 body is {} on x402 v2 — read the payment-required header, not the body.
• Free docs surfaces: / (catalog with prices), /llms.txt, /openapi.json, /health.
• Everything settles on-chain (Base mainnet USDC) — no chargebacks, no keys to revoke.

Catalog: https://sigtap-outreach-api.sigtap.workers.dev — free previews for every route, so you can wire the client before funding anything.