One Line of Code.
Instant API Monetization.
A production-ready SDK for pay-per-call APIs using USDC micropayments. Perfect for AI agents, microservices, and any programmatic client that needs simple, automatic payments.
import { createX402Middleware } from "@metar/metar-provider";
app.post("/api/generate",
createX402Middleware({
price: 0.03, // 0.03 USDC
payTo: "YOUR_WALLET...",
chain: "solana-mainnet"
}),
async (req, res) => {
// Payment verified!
res.json({ result: "..." });
}
);import { MetarClient } from "@metar/metar-client";
const client = new MetarClient({
agentKey: process.env.TAP_KEY,
wallet: mySolanaWallet
});
// Auto-handles 402 & payment
const res = await client.request("generate", {
method: "POST",
body: JSON.stringify({ prompt: "Hello world" })
});Payments should be simple.
Metar is a production-ready SDK that enables pay-per-call monetization for any API. It allows AI agents, microservices, and programmatic clients to pay for resources instantly using USDC on Solana.
For API Providers
Monetize your API endpoints instantly. No subscription management, no invoicing, just direct USDC deposits for every valid request.
For Programmatic Clients
Access premium APIs without credit cards or signups. Just fund a wallet and start making requests. Perfect for AI agents and microservices.
For Developers
Integrate in minutes with a simple Express middleware and a type-safe client SDK. Built on standard HTTP 402 status codes.
The Problem with Subscriptions
Inefficient for Agents
AI agents can't fill out credit card forms or manage monthly subscriptions. They need a programmatic way to pay for what they use.
High Overhead
Managing Stripe integration, webhooks, and invoicing for micro-transactions is expensive and complex.
API Key Leakage
Static API keys are a security risk. If leaked, you're liable for the bill. Metar uses cryptographic signatures for every request.
The Metar Solution
Metar standardizes the HTTP 402 Payment Required status code. When a client makes a request, the provider responds with a 402 and a payment invoice. The client SDK automatically signs and sends the payment, and the provider fulfills the request.
Technical Architecture
Metar orchestrates a secure, stateless payment flow between AI agents and API providers, verified on the Solana blockchain.
Client (AI Agent)
- Price Lookup
- USDC Transfer
- TAP Signature
Provider (API)
- Verify Headers
- Check On-Chain
- Log Usage
Solana Blockchain
- Confirm Tx
- USDC Settlement
- Immutable Record
Payment Flow
1. Price Discovery
Client requests price from GET /.meter/price. Returns price (USDC), recipient, and token mint.
2. Payment Transaction
Client creates and sends USDC transfer on Solana with a memo containing the route ID and nonce.
3. TAP Signature
Client generates HTTP Signature (RFC 9421) using Ed25519 to prove agent identity cryptographically.
4. API Request
Client makes request with x-meter-* headers and Authorization signature.
5. Verification
Provider middleware verifies timestamp, nonce, signature, and on-chain payment confirmation.
POST /api/generate HTTP/1.1
Host: api.provider.com
x-meter-tx: 5Kj3...9zXy
x-meter-route: summarize:v1
x-meter-amt: 0.03
x-meter-currency: USDC
x-meter-nonce: 018b...7f2a
x-meter-ts: 1709...8821
Authorization: Signature keyId="agent-1",...
Everything you need to monetize your API.
Metar provides a complete toolkit for building pay-per-call APIs. From the middleware that verifies payments to the client SDK that handles them automatically.
Provider Middleware
Monetize in minutes. One-line middleware protects any Express route. Automatic on-chain verification and usage analytics included.
Client SDK
Zero human intervention. SDK handles price lookup, USDC payments, and TAP signatures automatically.
Enterprise Security
Built on Visa's Trusted Agent Protocol. Ed25519 signatures, replay protection, and timestamp validation.
Solana Speed
Sub-second finality and low fees. Built for high-frequency machine-to-machine transactions.
Usage Analytics
Built-in SQLite tracking for payments and usage. Visualize revenue and request metrics in real-time.
Replay Protection
Nonces tracked per agent. Transaction signatures prevent double-spending and ensure idempotency.
Built on modern standards.
Metar is a monorepo designed for modularity and type safety. It leverages the best-in-class tools for Solana development and Node.js services.
Core Technologies
Node.js & TypeScript
Robust, type-safe runtime for high-performance API services.
Solana Blockchain
High-throughput, low-latency L1 for instant settlement.
USDC Stablecoin
Digital dollar for stable, predictable pricing.
Ed25519 Signatures
Cryptographic verification for secure authentication.
Package Structure
@metar/metar-client
Client SDK for agents to discover prices and make payments.
@metar/metar-provider
Express middleware for payment verification and replay protection.
@metar/agent-registry
Agent key registry and price service for centralized management.
@metar/dashboard
React/Vite dashboard for analytics and revenue tracking.
@metar/shared-types
TypeScript definitions for the TAP protocol and payment interfaces.
@metar/shared-config
Shared configuration constants (Solana networks, USDC mints).
@metar/facilitator
Facilitator mode for delegated payment verification (optional).
Documentation & Integration
Detailed API specifications and security requirements for integrating Metar.
API Specifications
GET/.meter/price
{
"price": 0.03,
"currency": "USDC",
"mint": "EPjFWdd5...",
"payTo": "7xKXtg2...",
"routeId": "summarize:v1",
"chain": "solana-devnet"
}Required Payment Headers
{
"x-meter-tx": "Solana transaction signature",
"x-meter-route": "Route identifier",
"x-meter-amt": "Payment amount",
"x-meter-currency": "USDC",
"x-meter-nonce": "Unique UUID v7",
"x-meter-ts": "Unix timestamp (ms)",
"x-meter-agent-kid": "Agent key ID",
"Authorization": "TAP signature"
}Security Requirements
Private Key Management
Never expose private keys in client-side code. Use secure key storage and rotation policies.
HTTPS Only
All production endpoints must use HTTPS. Payment headers contain sensitive information.
Nonce Management
Nonces must be unique per agent. Implement proper storage (Redis/DB) to prevent replay attacks.
POST /api/generate HTTP/1.1 Host: api.provider.com x-meter-tx: 5Kj3...9zXy x-meter-route: summarize:v1 x-meter-amt: 0.03 x-meter-currency: USDC x-meter-nonce: 018b...7f2a x-meter-ts: 1709...8821 Authorization: Signature keyId="agent-1",...Ready to monetize your APIs?
Join the first payment protocol built for the programmatic economy. Start integrating Metar today.