Machine payments with USDC on Base. No API key or subscription needed — pay per query directly from any wallet or AI agent.

What is x402?

x402 is an open HTTP payment protocol that revives the long-dormant HTTP 402 "Payment Required" status code. Instead of managing API keys and subscriptions, clients pay small amounts of USDC on Base for each request they make. The protocol is designed to be machine-native: AI agents, scripts, and bots can autonomously pay for data without human interaction.

Learn more at x402.org.

Why x402?

• No signup required— skip account creation, API key management, and subscription billing entirely.
• AI agent native— autonomous agents can fund themselves from a wallet and call APIs independently.
• Pay only for what you use— each query costs $0.01 in USDC. No monthly minimums or overage charges.
• Works with any USDC wallet— Base Sepolia for testing, Base Mainnet for production. Standard EIP-3009 authorization.
• Open standard— not a proprietary protocol. Any x402-compatible client works out of the box.

Pricing

USDC uses 6 decimal places. 10,000 units = $0.01 USD.

The Payment Flow

1. 1

   Client makes a request without payment

   Send a normal GET request to the endpoint. No headers needed on this first call.

2. 2

   Server responds with 402 Payment Required

   The server returns HTTP 402 with a PAYMENT-REQUIRED header (base64-encoded JSON) describing payment requirements: amount, token, network, and recipient address. The full requirements are also included in the JSON response body.

3. 3

   Client creates an EIP-3009 signed authorization

   The client signs a USDC transfer authorization using EIP-3009 (transferWithAuthorization). This is a gasless signature — no on-chain transaction yet. x402 client libraries handle this automatically.

4. 4

   Client retries with PAYMENT-SIGNATURE header

   Retry the request with the PAYMENT-SIGNATURE header set to the base64-encoded payment payload (signed authorization + metadata).

5. 5

   Server verifies and settles, then returns data

   The server calls the x402 facilitator to verify and settle the payment on-chain. On success, it returns HTTP 200 with your search results and a PAYMENT-RESPONSE header confirming the transaction.

Endpoint: Search

x402 Headers

Code Examples

from x402.httpx import X402Client
import httpx

# Set up client with your wallet private key
client = X402Client(
    httpx.Client(),
    private_key="0xYOUR_PRIVATE_KEY",   # wallet that holds USDC on Base Sepolia
    network="eip155:84532",               # Base Sepolia testnet
)

response = client.get(
    "https://mentibus.xyz/api/v1/x402/search",
    params={"q": "openai", "type": "companies", "limit": 5},
)

data = response.json()
print(data["data"]["companies"])
print("Paid via tx:", data["meta"]["transaction"])

import { createX402Fetch } from "@x402/fetch";
import { privateKeyToAccount } from "viem/accounts";
import { baseSepolia } from "viem/chains";

const account = privateKeyToAccount("0xYOUR_PRIVATE_KEY");

const fetchWithPayment = createX402Fetch({
  account,
  chain: baseSepolia,
});

const response = await fetchWithPayment(
  "https://mentibus.xyz/api/v1/x402/search?q=openai&type=companies&limit=5"
);

const data = await response.json();
console.log(data.data.companies);
console.log("Transaction:", data.meta.transaction);

# Step 1: First request — no payment header → server returns 402
curl -i "https://mentibus.xyz/api/v1/x402/search?q=openai&type=companies"

# HTTP/1.1 402 Payment Required
# PAYMENT-REQUIRED: eyJ4NDAyVmVyc2lvbiI6Miwi...  (base64 JSON)
# Content-Type: application/json
#
# {"x402Version":2,"error":"Payment required","accepts":[{...}]}

# Step 2: Decode the requirements, sign an EIP-3009 authorization with
# your wallet, then retry with PAYMENT-SIGNATURE header:
#
# (signing is done by an x402 library — shown here as a placeholder)
PAYMENT_SIG=$(python3 -c "
import base64, json
# In reality: sign the payment authorization with your wallet
payload = {'type': 'eip3009', 'signature': '0x...', 'from': '0x...', ...}
print(base64.b64encode(json.dumps(payload).encode()).decode())
")

curl "https://mentibus.xyz/api/v1/x402/search?q=openai&type=companies" \
  -H "PAYMENT-SIGNATURE: $PAYMENT_SIG"

# HTTP/1.1 200 OK
# PAYMENT-RESPONSE: eyJzdWNjZXNzIjp0cnVlLCJ0c...  (base64 JSON with tx hash)
# Content-Type: application/json
#
# {"data":{"companies":[...],"people":[],"investors":[]},"meta":{...}}

Response Format

{
  "data": {
    "companies": [
      {
        "id": 1,
        "name": "OpenAI",
        "slug": "openai",
        "logo": "https://...",
        "tagline": "...",
        "overview": "...",
        "website": "https://openai.com",
        "company_stage": "growth",
        "funding_stage": "series_d",
        "total_funding_usd": "11300000000.00",
        "founded_date": "2015-12-11",
        "employee_count": 1500,
        "is_verified": true
      }
    ],
    "people": [...],
    "investors": [...]
  },
  "meta": {
    "query": "openai",
    "type": "all",
    "page": 1,
    "limit": 10,
    "total": 3,
    "payer": "0xAbCd...1234",
    "transaction": "0x7f3b...ef90",
    "network": "eip155:84532",
    "price_paid": "10000",
    "price_paid_usd": "0.01"
  }
}

{
  "x402Version": 2,
  "error": "Payment required",
  "resource": {
    "url": "https://mentibus.xyz/api/v1/x402/search",
    "description": "Search companies, people, and investors",
    "mimeType": "application/json"
  },
  "accepts": [
    {
      "scheme": "exact",
      "network": "eip155:84532",
      "maxAmountRequired": "10000",
      "payTo": "0x...",
      "asset": "0x036CbD53842c5426634e7929541eC2318f3dCF7e",
      "maxTimeoutSeconds": 300,
      "description": "Search via USDC on Base"
    }
  ]
}

{
  "success": true,
  "transaction": "0x7f3b...ef90",
  "network": "eip155:84532",
  "payer": "0xAbCd...1234"
}

Networks

The server switches networks based on the X402_NETWORK environment variable. Set it to mainnet for production; it defaults to Base Sepolia.

FAQ