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Overview

x402 is an HTTP-native payment protocol that enables pay-per-request API access using USDC on Base Mainnet. With x402, you can access Messari endpoints without a Messari account or API key — simply pay per request with crypto. When to use x402:

AI Agents

Autonomous agents that need to query Messari data without managing API keys or subscriptions

Automated Pipelines

Data pipelines that require one-off or sporadic queries billed directly on-chain

One-Off Queries

Quick queries without signing up for an account or committing to a subscription

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Supported Endpoints

The following endpoints accept x402 payments:
EndpointMethodPrice
/ai/v2/chat/completionsPOST$0.25 / request

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Prerequisites

Before making a payment, ensure you have:
  • An EVM-compatible wallet (e.g. MetaMask, Coinbase Wallet)
  • USDC on Base Mainnet — a minimum of ~$1 is recommended to start
  • A small amount of ETH on Base Mainnet for gas fees

Bridge to Base

Use bridge.base.org to move USDC from Ethereum or another chain onto Base Mainnet.

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How It Works

x402 follows a simple 3-step flow: Step 1: Make a request Send your request to the Messari API without an API key. The gateway responds with HTTP 402 Payment Required along with payment requirements (amount, currency, recipient address, network). Step 2: Sign & pay Your x402-enabled client signs a USDC TransferWithAuthorization EIP-3009 message using your wallet’s private key. No gas is required for the authorization itself — the gateway submits the on-chain transaction on your behalf. Step 3: Request fulfilled The gateway verifies the signed authorization, collects the USDC payment, and proxies your original request. The API response is returned as normal.

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Quick Start (TypeScript)

Install the x402 fetch wrapper: 
npm install @x402/fetch @x402/evm viem
Make your first pay-per-request call: 
import { wrapFetchWithPaymentFromConfig } from '@x402/fetch';
import { ExactEvmScheme } from '@x402/evm';
import { privateKeyToAccount } from 'viem/accounts';

const account = privateKeyToAccount('0xYOUR_PRIVATE_KEY');

const fetchWithPayment = wrapFetchWithPaymentFromConfig(fetch, {
  schemes: [{ network: 'eip155:8453', client: new ExactEvmScheme(account) }],
});

const response = await fetchWithPayment('https://api.messari.io/ai/v2/chat/completions', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    messages: [{ role: 'user', content: 'What is the latest on Bitcoin?' }],
    verbosity: 'succinct',
    response_format: 'markdown',
    stream: false,
  }),
});

const data = await response.json();
console.log(data);
Never hardcode your private key in source code. Use environment variables: privateKeyToAccount(process.env.PRIVATE_KEY as \0x$`)`.

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Troubleshooting

“Payment verification failed” Your wallet does not have sufficient USDC on Base Mainnet. Check your balance and ensure you have enough USDC plus a small amount of ETH for gas. “Unsupported network” You must use eip155:8453 (Base Mainnet). Payment sent but no response received On-chain confirmation can take ~30 seconds. If you do not receive a response after 60 seconds, check the transaction status on Basescan. If the transaction is confirmed but you still received no response, contact api@messari.io.