Pay-per-secret API for AI agents

The endpoint

POST https://app.secretwolf.io/api/x402/secrets

Anonymous and pay-per-use. The agent sends the secret; the response is a single-view link (https://get.secretwolf.io/s/…) to hand to its human. The payload is AES-256-GCM encrypted, revealed exactly once, then hard-deleted — the API never returns or logs the plaintext.

How payment works (x402)

x402 revives HTTP 402 Payment Required. It's one request and a retry: the endpoint answers 402 with the price; the agent's x402 client signs a USDC payment on Base and retries; a facilitator settles it and the endpoint returns 200 with the link. Any x402-capable client handles the handshake — the agent just needs a funded wallet.

curl -i -X POST https://app.secretwolf.io/api/x402/secrets \
  -H "content-type: application/json" \
  -d '{"text":"AKIA...the secret value..."}'
# -> 402 Payment Required. An x402 client signs a $0.10 USDC payment and retries.

On success:

{
  "url": "https://get.secretwolf.io/s/8Kf3PunwGEt7hELi…",
  "id": "8Kf3PunwGEt7hELi…"
}

Protocol details

The endpoint speaks x402 version 2. The challenge arrives base64-encoded in a PAYMENT-REQUIRED response header; your client returns its signed authorisation in PAYMENT-SIGNATURE and gets a settlement receipt back in PAYMENT-RESPONSE. The legacy v1 header name X-PAYMENT is still accepted, so an older client isn't locked out.

• Scheme — exact.
• Network — eip155:8453, which is Base mainnet in CAIP-2 form.
• Asset — USDC, at $0.10 per secret. Read asset and payTo from the live challenge rather than pinning them.
• Identity, optional — if your agent implements Web Bot Auth, send a Signature-Agent header carrying the absolute https URL of your HTTP Message Signatures key directory. We record it against the payment so a repeat caller stays recognisable across wallet addresses. It costs nothing, changes nothing and gates nothing — we don't verify the signature, so it's a label rather than a credential.

A malformed request is rejected with 400 before any payment is taken, so an agent is never charged for a call that couldn't have produced a secret.

Example (TypeScript, x402-fetch)

import { wrapFetchWithPayment } from "x402-fetch";
import { createWalletClient, http } from "viem";
import { base } from "viem/chains";

// A wallet funded with USDC on Base (the agent controls it).
const pay = wrapFetchWithPayment(fetch, createWalletClient({ account, chain: base, transport: http() }));

const res = await pay("https://app.secretwolf.io/api/x402/secrets", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({ templateKey: "api-key", fields: { key: newApiKey } }),
});
const { url } = await res.json(); // hand this one-time link to the human

Send free text, or a typed template (website-login, dns-account, api-key, custom) via templateKey + fields. Text/template only, always one-time-use. A malformed request is rejected before any payment is taken.

Agent-to-agent

The recipient can be another agent, not just a human. Instead of the web page, it consumes the secret over JSON — POST /api/x402/secrets/{id}/reveal returns the value exactly once (free; the 256-bit link is the capability), then it's destroyed and audited. So one agent can provision a credential and hand it straight to another, single-use.

Discovery

The endpoint publishes x402 discovery metadata (service SecretWolf, tags secret, one-time, credentials) so x402-native agents can find it, and it's described for LLMs at /llms.txt. Full request/response reference is in the API docs.

Machine-readable: OpenAPI 3.1 for both endpoints, with request and response schemas. Point a client generator or an agent framework straight at it.