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Payments (x402) — @lucid-fdn/pay

The @lucid-fdn/pay package provides a drop-in replacement for the fetch() function, enabling automatic x402 payments for AI agents. It supports multiple blockchain networks, including Base, Ethereum, Arbitrum, Optimism, Polygon, ApeChain, Monad, Solana, and Sui.

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Installation

To get started, install the package using npm: 
npm install @lucid-fdn/pay

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Quick Start

Here’s a quick example to demonstrate how to use @lucid-fdn/pay: 
import { createWalletClient, http } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { base } from "viem/chains";
import { createLucidFetch, ViemWallet } from "@lucid-fdn/pay";

const client = createWalletClient({
  account: privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`),
  chain: base,
  transport: http(),
});

const lucidFetch = createLucidFetch({
  wallet: new ViemWallet(client),
  maxAmountPerRequest: "100000", // 0.10 USDC (6 decimals)
});

// Use exactly like fetch() -- payments are handled automatically
const response = await lucidFetch(
  "https://api.lucid.foundation/v1/chat/completions",
  {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({
      model: "gpt-4o",
      messages: [{ role: "user", content: "Hello" }],
    }),
  },
);

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How It Works

  1. Your request is sent to the API as a normal fetch() call.
  2. If the server returns HTTP 402, the response body contains an x402 v2 options[] array — one entry per supported chain and facilitator, each with the recipient address, token, amount, and chain.
  3. @lucid-fdn/pay selects the option matching your wallet’s chain (or falls back to the first option), checks the amount against your budget, sends an on-chain USDC transfer, and retries with X-Payment-Proof (tx hash) and X-Payment-Chain headers.
  4. The server delegates verification to the appropriate facilitator and returns the response.
This setup works with any x402-enabled API, including Lucid TrustGate and MCPGate endpoints.

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Supported Chains

ChainTokenFacilitators
BaseUSDCDirect, Coinbase, PayAI, Thirdweb
EthereumUSDCPayAI, Thirdweb
ArbitrumUSDCPayAI, Thirdweb
OptimismUSDCPayAI, Thirdweb
PolygonUSDCThirdweb
ApeChainUSDCThirdweb
MonadUSDCDirect, PayAI, Thirdweb
SolanaUSDCPayAI
SuiUSDCSui (native)

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API Reference

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createLucidFetch(config): lucidFetch

This function returns a configured fetch function that automatically handles x402 payments. 
const lucidFetch = createLucidFetch(config);
const response = await lucidFetch(url, init);

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lucidFetch(url, init?, config?)

A one-shot convenience function that accepts an inline config as the third argument. If no config is provided, it behaves as a standard fetch(). 
import { lucidFetch } from "@lucid-fdn/pay";

const response = await lucidFetch(
  "https://api.lucid.foundation/v1/chat/completions",
  { method: "POST", body: "..." },
  { wallet: myWallet },
);

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Configuration (LucidPayConfig)

OptionTypeDefaultDescription
walletPaymentWalletrequiredWallet adapter used for payments
maxAmountPerRequeststringno limitMaximum amount per request in micro-units (USDC has 6 decimals, so "1000000" = 1 USDC)
maxRetriesnumber1Number of retries after payment
onPayment(info: PaymentInfo) => void—Called after a successful payment
onPaymentSkipped(info) => void—Called when a payment exceeds the budget

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Per-Request Overrides (LucidFetchOptions)

This extends the standard RequestInit and allows you to override the wallet or budget on individual requests: 
const response = await lucidFetch(url, {
  method: "POST",
  body: "...",
  wallet: alternateWallet, // override wallet for this call
  maxAmount: "50000",      // override budget for this call
});

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PaymentInfo

The object passed to the onPayment callback includes:
FieldTypeDescription
txHashstringOn-chain transaction hash
amountstringAmount paid (micro-units)
recipientstringPayment recipient address
chainstringChain identifier (e.g. "base-sepolia")
tokenstringToken symbol (e.g. "USDC")
urlstringThe URL that required payment

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Wallets

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ViemWallet (production)

This wallet wraps a viem WalletClient to sign and send real ERC-20 transfers on-chain. Consumers need to bring their own viem dependency. 
import { createWalletClient, http } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { base } from "viem/chains";
import { ViemWallet } from "@lucid-fdn/pay";

const wallet = new ViemWallet(
  createWalletClient({
    account: privateKeyToAccount("0x..."),
    chain: base,
    transport: http(),
  }),
);

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MemoryWallet (testing)

An in-memory wallet that records payments without sending real transactions. This is useful for tests and local development. 
import { MemoryWallet } from "@lucid-fdn/pay";

const wallet = new MemoryWallet("0xYourAddress", "base-sepolia");

// After running requests:
console.log(wallet.payments); // array of recorded payments

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Custom Wallets

You can implement the PaymentWallet interface to use any signing backend: 
import type { PaymentWallet } from "@lucid-fdn/pay";

const myWallet: PaymentWallet = {
  address: "0x...",
  chain: "base",
  async sendPayment({ to, amount, tokenAddress, chain }) {
    // Sign and broadcast an ERC-20 transfer
    return txHash;
  },
};

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License

MIT