What is the X402 Protocol?
X402 is an open payment protocol built on HTTP 402 Payment Required. It enables machine-to-machine API payments using cryptocurrency. When an AI agent requests an X402-enabled endpoint, the server responds with a 402 status code and payment details. The agent's payment facilitator completes the crypto transaction automatically, and the server verifies payment then delivers the response. No API keys, subscriptions, or manual signup required. Any agent that can pay can access any X402 service instantly.
What is x402 List?
x402 List is the open directory of all services implementing the X402 payment protocol. It provides real-time monitoring, uptime statistics, and pricing data for every listed API endpoint. The directory is agent-first — designed primarily for consumption by AI agents via a structured JSON API, while remaining fully browsable by humans. Services are checked continuously and ranked by reliability, response time, and cost.
How X402 Works
- 1. Agent sends an HTTP request to an X402-enabled endpoint.
- 2. Server responds with HTTP 402 and an
accepts[]payload describing accepted payment methods, amounts, and network details. - 3. The agent's payment facilitator reads the payload and completes the crypto payment on the specified network.
- 4. Server verifies the on-chain payment and returns the requested data in the response body.
The entire flow is automatic. Agents handle payment without human intervention. Servers enforce payment at the HTTP layer, before any business logic executes.
How to Submit a Service
If you run an API that implements the X402 protocol, you can list it in the directory
for free. Submit your service at /submit with your endpoint URL,
description, supported networks, and pricing. Submissions are verified automatically —
we probe your endpoint to confirm it returns a valid 402 response with a well-formed
accepts[] payload. Once verified, your service appears in the directory
and monitoring begins immediately.
API Access
The full x402 List directory is available as structured JSON at /api. The API returns every listed service with current uptime, pricing, response times, and endpoint details. It is designed for programmatic consumption by AI agents, aggregators, and developer tools. No authentication required. Responses include pagination and filtering parameters for large result sets.
Contact
Questions? Reach us at hello@x402-list.com