How to Check an x402 Endpoint Before Paying

You can check an x402 endpoint before paying by using Lumière PayCheck. It provides a trust score and a clear verdict on whether the API is safe to use. This tool helps AI agents avoid scams and bad services without moving any money itself.

Why You Need a Pre-Payment Check

The x402 protocol allows APIs to ask for payment directly in the HTTP response. When an API returns a 402 status code, it includes a quote with the price, network, token, and a wallet address to pay. The client pays and then repeats the request with proof of payment. This system works without accounts or API keys. However, this simplicity creates risk. A valid 402 quote only proves that a payment method exists. It does not prove that the service will deliver data. It also does not prove that the wallet is stable or safe.

Lumière PayCheck solves this problem. It monitors over 128,000 x402 endpoints listed in the x402 Bazaar. It checks these endpoints every few hours. The tool looks at the validity of the quote, the stability of the price, and the health of the payout wallet. It also makes real paid test calls to confirm that the endpoint actually delivers what it advertises. A 402 quote or a payment receipt only shows that money changed hands. It does not show that the data was delivered. PayCheck confirms delivery with its own small payments.

How to Use the Free Web Checker

The easiest way to check an endpoint is through the web interface. This tool is free and requires no code. You can paste any x402 URL into the checker at https://lumierepaycheck.org/check. The tool returns a quick grade and verdict. This helps you decide if an endpoint is reliable.

The checker uses data from Lumière PayCheck to give a clear assessment. It monitors quote validity, price stability, and payout wallet history. You can also view detailed information for specific sellers in the x402 seller directory at https://lumierepaycheck.org/sellers. If you need to add an endpoint that is not yet monitored, you can submit it via POST to https://lumierepaycheck.org/v1/endpoints/submit. Checking one we do not monitor automatically adds it to the system.

Using the API or MCP Server for Agents

AI agents need programmatic access to check endpoints before they pay. Lumière PayCheck provides a REST API and an MCP server for this purpose. The free API endpoint is GET /v1/score?url=<endpoint>. This call returns a score from 0 to 100 and a verdict. The verdict is one of three options: proceed, caution, or avoid.

For agents built with Model Context Protocol (MCP), you can use the remote server at https://lumierepaycheck.org/mcp or the npm package lumiere-paycheck-mcp. The available tools include check_endpoint and check_payment. These tools allow your agent to verify a quote before sending funds. After paying, your agent can use the report_outcome tool to tell PayCheck if it received the expected data. This feedback loop helps improve the trust scores for everyone.

Understanding the Verdicts and Scores

The system analyzes several factors to create its verdict. It monitors 128,832 endpoints as of November 9, 2026. The current distribution shows that many endpoints are in a caution state. There are also bulk listings that may not be graded individually. The system flags specific risks such as payout wallet changes, price increases, and lookalike sellers. It screens all wallets against the OFAC sanctions list to prevent illegal transactions.

The score reflects the stability of the endpoint. A high score indicates a stable price, a consistent payout wallet, and successful paid tests. A low score might indicate recent wallet changes or failed tests. The system reads real USDC settlements on Base and Solana to calculate 30-day volume and the number of independent buyers. This data helps distinguish between legitimate services and potential scams.

For Sellers: Proving Your Trustworthiness

Sellers can use PayCheck to prove their reliability. You can fund a paid test of your own endpoint. The money used for this test goes back to your payout wallet. Once the test is complete, you can display a live badge on your documentation. This badge shows that your endpoint has passed independent verification. It helps buyers trust your service before they pay.

You can check your own endpoint and get a badge at https://lumierepaycheck.org/sellers/check. You can also view all monitored endpoints grouped by seller in the x402 seller directory at https://lumierepaycheck.org/sellers. This directory allows buyers to see the verdicts for every endpoint you operate.

FAQ

What is the difference between a 402 quote and a PayCheck score? A 402 quote is just a request for payment from an API. It does not guarantee service quality. A PayCheck score is an independent assessment of reliability, security, and delivery success based on real test payments.

Does Lumière PayCheck hold my money? No. PayCheck never moves anyone's money. It does not process payments, run channels, or issue receipts for other people's transactions. It only checks the endpoint before you pay.

How often are endpoints updated? The system monitors over 128,000 endpoints every few hours. This frequent checking ensures that the trust scores reflect the current status of the API and its payout wallet.

Check an endpoint for free at https://lumierepaycheck.org/