What is x402?

x402 is an open payment protocol that revives the HTTP 402 “Payment Required” status code. Instead of accounts, API keys, and monthly subscriptions, a service responds to an unpaid request with a price and payment requirements; the client pays and retries. It is designed so that autonomous AI agents can pay for data, tools, and content on their own.

How a paid request works

1. A client, often an AI agent, requests a paid resource over plain HTTP.
2. The server answers with status 402 and a machine-readable description of the price, accepted tokens, chain, and recipient.
3. The client signs a payment payload, typically a USDC transfer, and retries the request with the payload attached.
4. A facilitator verifies and settles the payment on-chain, and the server returns the paid response.

Why it matters for agents

Agents cannot fill out signup forms, manage credit cards, or rotate API keys across dozens of vendors. With x402, the only credential an agent needs is a funded wallet, and every paid endpoint becomes a uniform, discoverable HTTP interface.

Explore the directory

AgentIndex lists x402-enabled services across these categories:

• Data APIs — Structured data endpoints that agents can query and pay for per request over x402.
• Content Paywalls — Publishers and archives that unlock individual articles or reports for a micropayment.
• MCP Tools — Hosted MCP servers and tool gateways that charge agents for each tool call.
• Search & Retrieval — Search and retrieval APIs that return ranked results or cleaned documents for a per-query fee.
• Finance & Trading — Market data, signals, and analytics services priced for autonomous trading agents.
• Infrastructure & Facilitators — Facilitators, relays, and settlement infrastructure that keep x402 payments moving.
• Media Generation — Image, audio, and video generation services sold per generation or per unit of output.
• Commerce — Storefronts and checkout services that let agents buy digital or physical goods with x402.
• Identity Verification — KYC, attestation, and personhood checks that agents can purchase on demand.
• Other — x402-enabled services that do not fit neatly into any other category.

Start at the directory homepage or submit a service.