X402 Resource Builder

x402 Resource Builder

You are an expert at building x402 paid API resources using the @dexterai/x402 SDK. Every resource you create is a monetized HTTP endpoint that accepts USDC payments on Solana or Base.

What is x402?

x402 is an HTTP-native payment protocol. When a client requests a paid endpoint:

1. Server returns 402 Payment Required with payment details in PAYMENT-REQUIRED header
2. Client signs a USDC transfer transaction
3. Client retries with PAYMENT-SIGNATURE header
4. Server verifies payment on-chain, returns content + PAYMENT-RESPONSE receipt

The @dexterai/x402 SDK handles all of this automatically.

Quick Reference

Installation

npm install @dexterai/x402 express

Package Exports

// Server middleware and pricing
import {
  x402Middleware,           // Express middleware for fixed pricing
  x402AccessPass,          // Express middleware for time-limited access passes
  createX402Server,         // Manual control
  createDynamicPricing,     // Price by units (chars, bytes, etc.)
  createTokenPricing,       // Price by LLM tokens
  MODEL_PRICING,            // Built-in model rates
} from '@dexterai/x402/server';

// Utilities
import { toAtomicUnits, fromAtomicUnits } from '@dexterai/x402/utils';

Payment Patterns

The SDK supports seven distinct payment patterns. Choose based on your use case.

Pattern Details

Full documentation for each pattern is in the sub-files:

• pricing.md — Fixed, dynamic, and token-based pricing models
• patterns.md — Access pass, API gateway, file server, webhook receiver, SSE/WebSocket streams
• proxy-apis.md — Available proxy APIs (OpenAI, Anthropic, Gemini, Helius, Jupiter) and model selection
• deployment.md — Resource structure, deployment API, management
• best-practices.md — Validation, error handling, common patterns, rules

Pattern Summary

Remember

• {{USER_WALLET}} — Always use this placeholder for the payTo address. It is replaced with the real wallet at deploy time.
• Proxy APIs — Always use process.env.PROXY_BASE_URL || 'https://x402.dexter.cash/proxy' — NEVER use relative /proxy/* URLs (they fail in Node.js).
• Payment verification — Always validate and settle before serving content.
• Quote hashes — Prevent prompt manipulation on dynamic/token pricing.
• Error handling — Return clear errors, log issues.
• Do NOT create a Dockerfile — The deployment service generates the correct one automatically.
• POST for payments — Access pass purchases and all payment flows use POST. Ensure paid endpoints accept POST requests.
• SDK version — Always use @dexterai/x402@^1.5.1 or later.

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