@bfcmath/x402-sdk

Typed client SDK for the api-server-onchain x402 search endpoints.

It wraps the two awkward parts of the flow:

• the initial 402 Payment Required challenge
• the follow-up payment-signature header generation

It also returns a serializable paymentContext object, including the original payment-signature, so another agent or process can keep working with the same paid search later.

Install

pnpm add @bfcmath/x402-sdk

Quick start

import {
  createOptimaiX402Client,
  createViemPaymentHandler,
} from "@bfcmath/x402-sdk";

const paymentHandler = createViemPaymentHandler({
  privateKey: process.env.X402_PAYER_PRIVATE_KEY!,
  rpcUrls: {
    "eip155:84532": "https://sepolia.base.org",
  },
});

const client = createOptimaiX402Client({
  baseUrl: "http://localhost:3002",
  paymentHandler,
});

const { search, paymentContext } = await client.createSearch({
  query: "What is liquidation?",
});

const completed = await client.waitForSearchCompletion(search.id, {
  paymentContext,
});

console.log(completed.result?.answer);

API

createOptimaiX402Client(config)

Creates the high-level SDK client.

Methods:

• createSearch(input, options?)
• getSearch(id, options?)
• cancelSearch(id, options?)
• waitForSearchCompletion(id, options?)
• rememberPaymentContext(context)
• forgetPaymentContext(id)

createViemPaymentHandler(config)

Creates a payment handler backed by @x402/evm, @x402/fetch, and viem.

Built-in network support:

• eip155:8453 -> Base
• eip155:84532 -> Base Sepolia

Persisting search access across agents

GET /external/v1/x402/search/:id works best when the client replays the exact original payment-signature used for the paid create call. Because of that, the SDK returns:

type SearchPaymentContext = {
  id: string;
  paymentRequired: X402PaymentRequired;
  paymentSignature?: string;
};

Persist this object alongside the search id if another agent or process will poll or fetch the search later:

const { search, paymentContext } = await client.createSearch({ query: "..." });

// store paymentContext somewhere durable

client.rememberPaymentContext(paymentContext);
const latest = await client.getSearch(search.id);

If you retry createSearch() with the same Idempotency-Key from another process, pass the previously stored context back in options.existingPaymentContext so the SDK can authenticate the 303 redirect target with the original signature:

const retry = await client.createSearch(
  { query: "..." },
  {
    idempotencyKey: "search-123",
    existingPaymentContext: paymentContext,
  },
);

Local smoke test

The package includes a smoke script for testing the built SDK against a live OptimAI x402 endpoint:

X402_PAYER_PRIVATE_KEY=0x... pnpm smoke:local

What to pass:

• X402_PAYER_PRIVATE_KEY must be the payer wallet private key used to sign the x402 payment payload
• this is a normal EVM wallet private key: 32-byte hex, with or without 0x
• it is not a server key, not a Coinbase facilitator key, and not an API key

If you use MetaMask:

• use the private key for the account that should pay for the x402 request
• in MetaMask, export the account private key and pass that exported value as X402_PAYER_PRIVATE_KEY
• the account should have enough funds on the chain required by the server challenge
• treat this key as highly sensitive and only use it in a secure local/dev environment you control

Defaults:

• OPTIMAI_X402_BASE_URL=https://api-onchain.optimai.network
• mainnet RPC for eip155:8453 defaults to https://mainnet.base.org

Optional overrides:

• OPTIMAI_X402_QUERY="What is liquidation?"
• OPTIMAI_X402_BASE_URL=http://localhost:3002
• X402_RPC_URL_BASE=https://mainnet.base.org
• X402_RPC_URL_BASE_SEPOLIA=https://sepolia.base.org
• OPTIMAI_X402_RUN_CANCEL=1

Local compatibility test

For a stronger end-to-end check against api-server-onchain, use:

X402_PAYER_PRIVATE_KEY=0x... OPTIMAI_X402_BASE_URL=http://localhost:3002 pnpm compat:local

This script validates the full x402 contract described in the server integration notes:

• create a paid search with query Compare ETH and BTC
• open GET /external/v1/x402/search/:id/events using the stored original payment-signature
• wait for search.completed and search.done
• verify the completed SSE answer matches the final GET /external/v1/x402/search/:id answer
• create a second search and verify DELETE /external/v1/x402/search/:id
• verify the cancelled search later returns:
  • status: "cancelled"
  • x402_payment_status: "voided"

If the script finishes with:

[result]
Compatibility test completed successfully.

then the SDK and the current api-server-onchain implementation are compatible for the tested create, SSE, GET, and DELETE flows.

Manual release checklist

First release is intentionally manual. From the package root:

pnpm install
pnpm build
pnpm test
X402_PAYER_PRIVATE_KEY=0x... OPTIMAI_X402_BASE_URL=http://localhost:3002 pnpm compat:local
pnpm pack

What to verify before publish:

• pnpm build succeeds
• pnpm test succeeds
• pnpm compat:local succeeds against a running api-server-onchain
• pnpm pack produces the tarball without missing entrypoints or type declarations

Publish steps:

npm whoami
npm publish --access public

Post-publish verification:

mkdir -p /tmp/optimai-x402-sdk-smoke
cd /tmp/optimai-x402-sdk-smoke
pnpm init
pnpm add @bfcmath/x402-sdk

Then import createOptimaiX402Client and createViemPaymentHandler from the installed package and run a smoke request against api-server-onchain.