x402 Payment Protocol

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Supported endpoints

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How it works

1. Send a request without authentication. The API responds with 402 Payment Required and a payment-required header containing the amount, deposit address, network, and asset.
2. Sign a USDC transfer (EIP-712 / EIP-3009) with your wallet, then resend the same request with the signed payload in the payment-signature header.
3. The API verifies the signature, executes the payment on-chain, and returns 200 with a payment-response header containing the transaction hash.

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Setting up a wallet

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Quickstart

pip install 'linkup-sdk[x402]'

from eth_account import Account
from linkup import LinkupClient
from linkup.x402 import create_x402_signer

account = Account.from_key("0xYOUR_PRIVATE_KEY")
signer = create_x402_signer(account)
client = LinkupClient(x402_signer=signer)

result = client.search(
    query="What is Linkup?",
    depth="standard",
    output_type="sourcedAnswer",
)
print(result.answer)

npm install linkup-sdk @x402/core @x402/evm viem

import { LinkupClient } from 'linkup-sdk';
import { createX402Signer } from 'linkup-sdk/x402';
import { privateKeyToAccount } from 'viem/accounts';

const account = privateKeyToAccount('0xYOUR_PRIVATE_KEY');
const signer = createX402Signer(account);
const client = new LinkupClient({ signer });

const result = await client.search({
  query: 'What is Linkup?',
  depth: 'standard',
  outputType: 'sourcedAnswer',
});
console.log(result);

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Headers reference