s402

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Tiny. Zero dependencies. Multi-language.

TypeScript (~30 KB) and Python implementations. No Sui SDK, no crypto libs bundled. Import the types, build your own stack.

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Works with x402 clients today

An x402 client can talk to your s402 server using the exact scheme — zero code changes. Migrate incrementally.

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Pay once, prepay, escrow, stream, or encrypt

One-shot transfers for simple calls. Prepaid deposits for 500x gas savings. Escrow for trustless commerce. Streams for real-time billing. Unlock for pay-to-decrypt.

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Built for agents that self-recover

Every error includes retryable and suggestedAction. Your agent knows whether to retry, top up, or switch schemes — no human needed.

See It in Action

An AI agent hits a paid API. The server says "pay me." The agent pays and gets the data. Three HTTP requests, zero human intervention.

typescript

import {
  extractRequirementsFromResponse,
  encodePaymentPayload,
  S402_HEADERS,
} from 's402';

async function agentFetch(url: string, buildPayment: PaymentBuilder) {
  const res = await fetch(url);

  if (res.status !== 402) return res;

  // 1. Decode what the server wants
  const requirements = extractRequirementsFromResponse(res);
  if (!requirements) throw new Error('Invalid 402 response');

  // 2. Build and sign a payment (you bring the chain SDK)
  const payment = await buildPayment(requirements);

  // 3. Retry with payment attached
  return fetch(url, {
    headers: { [S402_HEADERS.PAYMENT]: encodePaymentPayload(payment) },
  });
}

s402 defines the wire format — what gets sent over HTTP. You bring your own chain SDK for the how (PTB builders, signers, RPC calls).

Python

python

import httpx
from s402 import decode_payment_required, encode_payment_payload, S402_HEADERS

url = "https://api.example.com/premium-data"
res = httpx.get(url)
if res.status_code == 402:
    requirements = decode_payment_required(res.headers[S402_HEADERS["PAYMENT_REQUIRED"]])
    payment = build_payment(requirements)  # you bring the chain SDK
    res = httpx.get(url, headers={S402_HEADERS["PAYMENT"]: encode_payment_payload(payment)})

bash

pip install s402   # Python — zero dependencies
npm install s402   # TypeScript — zero dependencies

v0.2.3 · Five payment schemes · 868 tests across TypeScript and Python · 132-vector conformance suite · Apache-2.0 · npm

s402Your AI agent needs to pay for things.