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Overview

x402 is a payment protocol for HTTP resources. When a client requests a payment-gated endpoint, the server responds with HTTP 402 and payment requirements. The client includes a payment proof in the X-Payment header, and the server verifies it via a facilitator before granting access. In aixyz, AixyzServer extends x402ResourceServer, providing built-in payment gating for agent and tool endpoints.

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How It Works

  1. Client requests a gated endpoint (e.g., POST /agent)
  2. Server returns HTTP 402 with payment requirements (price, network, payTo address)
  3. Client constructs payment proof and retries with X-Payment header
  4. Server verifies payment via a facilitator and grants access

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The accepts Export

Define payment requirements by exporting accepts from your agent or tool: 
import type { Accepts } from "aixyz/accepts";

export const accepts: Accepts = {
  scheme: "exact",
  price: "$0.005",
};
This gates the endpoint behind a $0.005 exact payment.

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With Overrides

export const accepts: Accepts = {
  scheme: "exact",
  price: "$0.005",
  network: "eip155:8453", // override config network
  payTo: "0x...", // override config payTo
};
Prices are USD strings: "$0.005", "$0.01", "$0.0001".

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Per-Agent and Per-Tool Pricing

Agents and tools can each declare their own accepts export, enabling granular pricing: 
// app/agent.ts — agent-level pricing
export const accepts: Accepts = {
  scheme: "exact",
  price: "$0.01",
};

// app/tools/premium-search.ts — tool-level pricing
export const accepts: Accepts = {
  scheme: "exact",
  price: "$0.001",
};
  • Agent accepts gates the A2A /agent endpoint
  • Tool accepts gates the tool on the MCP /mcp endpoint
  • Agents and tools without accepts are not registered on protocol endpoints

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Facilitators

Payment verification is handled by a facilitator service:
FacilitatorActivationURL
DefaultAlways availablehttps://www.x402.org/facilitator
Coinbase CDPWhen CDP_API_KEY_ID is setAuto-configured
CustomSet X402_FACILITATOR_URLYour custom URL

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Custom Facilitator

Create app/accepts.ts to provide a custom facilitator: 
import { HTTPFacilitatorClient } from "aixyz/accepts";

export const facilitator = new HTTPFacilitatorClient({
  url: process.env.X402_FACILITATOR_URL ?? "https://www.x402.org/facilitator",
});

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Server Integration

In a custom server, use withX402Exact() to add payment middleware: 
server.withX402Exact("POST /agent", {
  scheme: "exact",
  price: "$0.005",
});

Agent Structure

Where to define accepts exports.

ERC-8004 Identity

On-chain agent identity for verified payments.