x402-resource-builder

name	x402-resource-builder
description	Build x402 paid API resources using @dexterai/x402 SDK v1.5.1. Creates monetized endpoints that accept USDC payments on Solana and Base.
version	2.0.0
author	Dexter
license	MIT
tags	["x402","payments","solana","base","api","monetization","dexter","access-pass"]

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.

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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

Pattern	Import	When to Use
Fixed Price	x402Middleware	Same price every request
Dynamic Price	createDynamicPricing	Price scales with input size
Token Price	createTokenPricing	LLM/AI token-based pricing
Access Pass	x402AccessPass	Pay once, unlimited requests for a time window
API Gateway	x402Middleware + proxy	Monetize any upstream API
File Server	x402Middleware per file	Pay-per-download with per-file pricing
Webhook Receiver	x402Middleware	Sender pays to deliver data
SSE/WS Stream	x402Middleware + SSE/WS	Pay for time-limited data streams

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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.