DEV Community: 吴增海

How I Built a 120-Endpoint x402 API Marketplace in a Weekend

吴增海 — Sun, 24 May 2026 12:13:32 +0000

How I Built a 120-Endpoint x402 API Marketplace in a Weekend (And Why It Matters)

Building the "Swiss Army Knife" for AI Agents on the x402 protocol

The Problem

I've been building on the x402 protocol — Coinbase's micropayment standard for AI agents. The idea is beautiful: agents call APIs, pay per request with USDC, no API keys, no subscriptions. It's the HTTP of agent commerce.

But there was a gap. When I looked at the existing services, they were all single-purpose:

BlockRun: AI chat completions
OttoAI: AI chat completions
Aubr: AI search

One API = one task. An agent that needs a price chart, a weather report, a blockchain lookup, and an AI chat — that's four different x402 integrations.

That's when I realized: nobody had built the "everything API" for agents.

The Idea

What if one API could do everything an agent needs?

Blockchain: 🪙 BTC price, gas fees, wallet balances, ENS lookup, DeFi insights
AI: 🤖 Chat, code, translation, image generation, video generation
Weather: 🌤️ Current, forecast, historical
Social: 🐦 Twitter, Discord, Telegram, Instagram, TikTok
Search: 🔍 Web search, arXiv, GitHub
E-commerce: 🛒 Product search, reviews
Finance: 💱 Forex, stocks, commodities
Utilities: ✉️ Email verification, IP lookup, domain WHOIS, URL shorten
Security: 🔐 AML screening, KYC verification, phishing detection
PI: 🏢 RWA, real estate, credit scoring, bond data

120 endpoints. 20+ categories. One API.

That's GoldBean.

The Tech Stack

The stack is refreshingly simple:

GoldBean = Express.js + x402 micropayments + ChatGPT

Architecture

┌─────────────┐     ┌─────────┐     ┌──────────────┐
│   AI Agent  │────▶│ nginx   │────▶│  GoldBean    │
│ (x402 SDK)  │     │ (SSL)   │     │ (Express.js) │
└─────────────┘     └─────────┘     └──────────────┘
                                            │
                                     ┌──────┴──────┐
                                     │  Base Chain  │
                                     │  (USDC on   │
                                     │  eip155:8453)│
                                     └─────────────┘

The flow is elegant:

Agent discovers GoldBean via /.well-known/x402 or /openapi.json
Agent calls /paid/llm-chat → gets back HTTP 402 Payment Required
402 response includes Payment-Required header (base64-encoded JSON: amount, network, payTo)
Agent pays via x402 → gets back a payment receipt → retries with it
GoldBean validates → serves the response

No API keys. No auth. No subscriptions. Just pay and use.

The Hardest Part: Getting Registered on x402scan

This deserves its own section because it took longer than building the API.

What x402scan expects

The x402scan scanner validates four things:

/.well-known/x402 — discovery endpoint
/openapi.json — the canonical API contract
/openapi.json has x-payment-info on paid endpoints
Endpoint returns proper HTTP 402 with Payment-Required header

The 402 Header Format (V2)

Here's the format that works (took 6+ iterations to nail):

{
  "x402Version": 2,
  "accepts": [{
    "scheme": "exact",
    "network": "eip155:8453",
    "amount": "40000",
    "asset": "0x833589f...",
    "payTo": "0x7484b0...",
    "maxTimeoutSeconds": 300
  }],
  "resource": {
    "url": "https://goldbean-api.xyz/paid/llm-chat",
    "description": "llm-chat",
    "mimeType": "application/json"
  }
}

Lessons learned:

x402Version must be a number (not string)
amount is in atomic units (USDC = 6 decimals, so $0.04 = "40000")
amount must be a string (not number)
Body must be empty {} (V2 moves all payment info to headers)
The response must have Cache-Control: no-store
Add BOTH Payment-Required AND x-payment-required headers for compatibility

I built an x402-check tool to verify format — it saved me hours of debugging.

The Schema Trap

Getting 31/120 endpoints registered was easy. The remaining 89 all failed with:

Missing input schema

The fix: every endpoint needs a proper input schema in OpenAPI so the scanner can construct a valid test request. A parameter like address for address lookups, prompt for chat endpoints, lat/lon for weather. The scanner reads the OpenAPI, builds a probe request, and expects 402. Without input schemas, it can't even probe.

What Running 120 Endpoints Actually Looks Like

The Good

One server process. One domain. One integration. 120 capabilities.

npx agentcash try https://goldbean-api.xyz

Boom. Your agent can now check BTC price, get a weather forecast, generate an image, analyze sentiment, and chat with an LLM — all through a single API with a single $USDC wallet.

The Reality Check

$0 revenue. 0 buyers. 0 transactions.

Registration doesn't equal usage. The next phase is getting actual agents to call the endpoints. That means:

Dev.to / Medium — telling the story
Community — showing up on x402 Discord/Twitter
Free trials — first 10 calls free to lower the barrier
Self-hosting — running automated calls to generate initial tx records (who wants to be the first buyer of a zero-tx service?)

What's Next

Phase	What	When
🚀	All 120 endpoints on x402scan	This week
📝	dev.to/Medium article series	This week
🐦	Twitter/X presence (@x402 ecosystem)	This week
🆓	Free trial mechanism	Next week
📊	Operations dashboard	Next week
🔌	Marketplace platform (3rd-party endpoints)	June

Why I'm Building This

The x402 protocol is going to be huge. 480,000+ agents already transacting, $165M+ in agent-to-agent commerce on Base chain.

But the infrastructure is still early. Most x402 services are single-purpose. GoldBean is my bet that agents need a general-purpose API — one they can call for anything, without worrying about "does this endpoint support x402?"

120 endpoints down. 200+ on the roadmap.

Let's see where this goes.

Built with ☕ and x402. Check us out: https://goldbean-api.xyz

How I Built a 120-Endpoint x402 API Marketplace in a Weekend (And Why It Matters)

吴增海 — Sun, 24 May 2026 12:12:43 +0000

How I Built a 120-Endpoint x402 API Marketplace in a Weekend (And Why It Matters)

Building the "Swiss Army Knife" for AI Agents on the x402 protocol

The Problem

But there was a gap. When I looked at the existing services, they were all single-purpose:

BlockRun: AI chat completions
OttoAI: AI chat completions
Aubr: AI search

One API = one task. An agent that needs a price chart, a weather report, a blockchain lookup, and an AI chat — that's four different x402 integrations.

That's when I realized: nobody had built the "everything API" for agents.

The Idea

What if one API could do everything an agent needs?

Blockchain: 🪙 BTC price, gas fees, wallet balances, ENS lookup, DeFi insights
AI: 🤖 Chat, code, translation, image generation, video generation
Weather: 🌤️ Current, forecast, historical
Social: 🐦 Twitter, Discord, Telegram, Instagram, TikTok
Search: 🔍 Web search, arXiv, GitHub
E-commerce: 🛒 Product search, reviews
Finance: 💱 Forex, stocks, commodities
Utilities: ✉️ Email verification, IP lookup, domain WHOIS, URL shorten
Security: 🔐 AML screening, KYC verification, phishing detection
PI: 🏢 RWA, real estate, credit scoring, bond data

120 endpoints. 20+ categories. One API.

That's GoldBean.

The Tech Stack

The stack is refreshingly simple:

GoldBean = Express.js + x402 micropayments + ChatGPT

Architecture

┌─────────────┐     ┌─────────┐     ┌──────────────┐
│   AI Agent  │────▶│ nginx   │────▶│  GoldBean    │
│ (x402 SDK)  │     │ (SSL)   │     │ (Express.js) │
└─────────────┘     └─────────┘     └──────────────┘
                                            │
                                     ┌──────┴──────┐
                                     │  Base Chain  │
                                     │  (USDC on   │
                                     │  eip155:8453)│
                                     └─────────────┘

The flow is elegant:

Agent discovers GoldBean via /.well-known/x402 or /openapi.json
Agent calls /paid/llm-chat → gets back HTTP 402 Payment Required
402 response includes Payment-Required header (base64-encoded JSON: amount, network, payTo)
Agent pays via x402 → gets back a payment receipt → retries with it
GoldBean validates → serves the response

No API keys. No auth. No subscriptions. Just pay and use.

The Hardest Part: Getting Registered on x402scan

This deserves its own section because it took longer than building the API.

What x402scan expects

The x402scan scanner validates four things:

/.well-known/x402 — discovery endpoint
/openapi.json — the canonical API contract
/openapi.json has x-payment-info on paid endpoints
Endpoint returns proper HTTP 402 with Payment-Required header

The 402 Header Format (V2)

Here's the format that works (took 6+ iterations to nail):

{
  "x402Version": 2,
  "accepts": [{
    "scheme": "exact",
    "network": "eip155:8453",
    "amount": "40000",
    "asset": "0x833589f...",
    "payTo": "0x7484b0...",
    "maxTimeoutSeconds": 300
  }],
  "resource": {
    "url": "https://goldbean-api.xyz/paid/llm-chat",
    "description": "llm-chat",
    "mimeType": "application/json"
  }
}

Lessons learned:

x402Version must be a number (not string)
amount is in atomic units (USDC = 6 decimals, so $0.04 = "40000")
amount must be a string (not number)
Body must be empty {} (V2 moves all payment info to headers)
The response must have Cache-Control: no-store
Add BOTH Payment-Required AND x-payment-required headers for compatibility

I built an x402-check tool to verify format — it saved me hours of debugging.

The Schema Trap

Getting 31/120 endpoints registered was easy. The remaining 89 all failed with:

Missing input schema

What Running 120 Endpoints Actually Looks Like

The Good

One server process. One domain. One integration. 120 capabilities.

npx agentcash try https://goldbean-api.xyz

Boom. Your agent can now check BTC price, get a weather forecast, generate an image, analyze sentiment, and chat with an LLM — all through a single API with a single $USDC wallet.

The Reality Check

$0 revenue. 0 buyers. 0 transactions.

Registration doesn't equal usage. The next phase is getting actual agents to call the endpoints. That means:

Dev.to / Medium — telling the story
Community — showing up on x402 Discord/Twitter
Free trials — first 10 calls free to lower the barrier
Self-hosting — running automated calls to generate initial tx records (who wants to be the first buyer of a zero-tx service?)

What's Next

Phase	What	When
🚀	All 120 endpoints on x402scan	This week
📝	dev.to/Medium article series	This week
🐦	Twitter/X presence (@x402 ecosystem)	This week
🆓	Free trial mechanism	Next week
📊	Operations dashboard	Next week
🔌	Marketplace platform (3rd-party endpoints)	June

Why I'm Building This

The x402 protocol is going to be huge. 480,000+ agents already transacting, $165M+ in agent-to-agent commerce on Base chain.

120 endpoints down. 200+ on the roadmap.

Let's see where this goes.

Built with ☕ and x402. Check us out: https://goldbean-api.xyz

GoldBean: 120+ Paid APIs for AI Agents via x402 Micropayments

吴增海 — Sun, 24 May 2026 03:15:26 +0000

GoldBean: 120+ Paid APIs for AI Agents via x402 Micropayments

GoldBean is an open x402-powered API marketplace that offers 120+ paid endpoints for AI agents, developers, and applications. Every call is settled instantly with USDC on Base via the x402 protocol — no subscriptions, no credit cards, just pay-per-use at micro prices ($0.01–$0.08 per call).

What is x402?

x402 is an open standard from the Coinbase ecosystem that lets HTTP APIs request micropayments by returning HTTP 402 Payment Required. The client signs a payment with their wallet, and the server verifies it through a facilitator (like Coinbase CDP). Think of it as "PayPal for AI agents" — but fully on-chain, non-custodial, and designed for machine-to-machine payments.

🚀 What GoldBean Offers

🧠 AI & Content Generation

Endpoint	Price	Description
`/paid/llm-chat`	$0.04	AI chat generation
`/paid/llm-embed`	$0.02	Text embedding
`/paid/llm-summary`	$0.02	Long document summarization
`/paid/llm-translate`	$0.02	Multi-language translation
`/paid/llm-code`	$0.04	Code generation
`/paid/image-gen`	$0.05	AI image generation
`/paid/image-analyze`	$0.03	Image recognition
`/paid/image-upscale`	$0.02	Image upscaling
`/paid/voice-2-text`	$0.03	Speech-to-text
`/paid/text-2-voice`	$0.02	Text-to-speech
`/paid/video-gen`	$0.08	Short video generation
`/paid/video-analyze`	$0.06	Video analysis

🔗 Blockchain & DeFi

Gas forecasts, ETH/BTC prices, token insights, whale alerts, NFT floor prices, DeFi positions, smart contract verification, cross-chain comparisons, mempool analysis, and more — all at $0.01–$0.05 per call.

🌐 Web & Search

Web search, web crawling, news (crypto + global), social media data (Twitter, Discord, Telegram, Weibo, Instagram, TikTok), sentiment analysis, weather, maps, and more.

📄 Office & Productivity

PDF parsing/merging, Excel/Word processing, OCR, barcode generation, email verification.

🛡️ Security & Compliance

KYC checks, AML screening, address risk analysis, phish detection, virus scanning, captcha solving.

💼 E-commerce & Logistics

Product info, reviews, search, express tracking, air tickets, hotel search.

📊 Finance

Stock prices, forex rates, commodity prices, fund NAV, crypto history, stablecoin rates.

🎮 Gaming & Metaverse

Game NFT items, game wallets, metaverse land data.

🛠️ How to Use

GoldBean endpoints work with any x402-compatible client. Here's a simple example:

# Call with x402-proxy (auto-pays the 402)
npx x402-proxy https://goldbean-api.xyz/paid/llm-chat?ref=myref

# Or use the MCP server (for Claude Desktop, Cursor, etc.)

MCP Integration

GoldBean is discoverable via Bazaar (the x402 service marketplace) and works with any MCP-compatible client. Add it to Claude Desktop, Cursor, or Windsurf by configuring the MCP server to point at GoldBean's Bazaar discovery endpoint.

💰 Pricing

All prices are in USDC on Base:

Price Range	Examples
$0.01–$0.02	Basic queries: weather, gas, crypto price, ENS resolve, QR code
$0.03–$0.05	Standard: LLM chat, image analysis, web search, KYC check
$0.06–$0.08	Premium: video generation, video analysis, AI agent stats

🔗 Links

Marketplace: goldbean-api.xyz
GitHub: github.com/wuzenghai616-lang/goldbean
Bazaar Discovery: https://goldbean-api.xyz/__bazaar
Wallet: 0x7484b0bca25d2ee56e9b0535572d4cf44a047d98 (Base)
Network: eip155:8453 (Base mainnet)

🎯 Roadmap

[ ] MCP wrapper package — npm install @goldbean/mcp for one-line Claude/Cursor setup
[ ] Subscription plans — Quant, Social, Merchant bundles at $29–$99/month
[ ] Cross-chain — Solana and Arbitrum support
[ ] Developer dashboard — Usage analytics, API keys, spending controls

Built with the x402 protocol. Payments verified via Coinbase CDP Facilitator. Part of the awesome-x402 ecosystem.