About the x402 Protocol and x402 List
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. The protocol is documented at x402.org.
What is x402 List?
x402 List is an agent-first directory of services implementing the x402
payment protocol. It is designed primarily for consumption by AI agents and automated
systems via a structured JSON API, and remains fully
browsable by humans. Every service entry, uptime metric, and
price point that appears on these pages is also available as machine-readable JSON at
/api/v1/*, described by an OpenAPI 3.1 specification,
and summarized for LLMs at /llms.txt and
/llms-full.txt. 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.
How do AI agents use x402 for payments?
AI agents send an HTTP request to an x402 endpoint. The server responds with HTTP 402 and payment details. The agent's payment facilitator completes the crypto transaction, and the server delivers the response. No API keys or subscriptions required.