Add a stablecoin paywall to any HTTP route.
In TypeScript, Rust, Go, Python, Ruby, PHP, Lua, Kotlin, or Swift.

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Why stablecoins?

Stablecoins are digital dollars (USDC, USDT, PYUSD, EURC, …) that move on public payment rails. For a developer building an API, a SaaS, or an agent that needs to pay for things, they unlock a few properties that classical card networks can't match:

• No middleman. Funds settle directly from payer to recipient. No gateway, no acquirer, no PSP holding the money for 2–30 days.
• No 2.9% + 30¢. Network fees are measured in fractions of a cent, not percentage points. Micro-transactions stop being a rounding error.
• No chargebacks. Payments are final once confirmed on-chain. Refunds happen because you choose to send one, not because a card network reversed it 90 days later.
• No accounts to open. Anyone with a wallet — a person, a script, an agent — can pay. No KYC dance before the first dollar moves.
• Programmable. Splits, fees, sponsored gas, subscriptions, refunds — all expressible as a transaction your server constructs.

Why Solana?

Solana is the most-used blockchain for payments today, and it's the one this kit is built on.

• ~200ms settlement. A buyer signs, your server sees the confirmation before the next render frame.
• ~$0.0013 median fee. Stable, even when the network is busy. Predictable enough to charge $0.001 for an API call without losing money on the transfer.
• ~$2T in stablecoin transfers per quarter. It's the rail Visa, PayPal, Stripe, and Western Union have all plugged into.
• 100% of the top 10 stablecoins. USDC, USDT, PYUSD, EURC — pick the asset that matches your accounting.

See payments.org for the long-form pitch.

What this repo gives you

Two open protocols, sharing one mental model: an HTTP server replies 402 Payment Required with a challenge, the client pays, and the same request is replayed with a proof of payment. The kit ships server and client SDKs for both.

• x402 — The minimalist take. Three-step handshake (request → 402 → pay → replay), single-recipient, the facilitator pays the network fee. Best for "one endpoint, one price, one wallet."
• MPP — The richer take. Same 402 handshake, but the challenge carries an intent that supports multi-recipient splits, server-side fee accounting, and a separate fee-payer signer. Best for marketplaces, platform fees, and gasless flows.

sequenceDiagram
    autonumber
    participant C as Client / Agent
    participant S as Your API
    participant Sol as Solana
    C->>S: GET /api/report
    S-->>C: 402 Payment Required<br/>{ amount: 0.10 USDC, pay_to, nonce }
    C->>Sol: sign & submit USDC transfer
    Sol-->>C: tx signature
    C->>S: GET /api/report<br/>X-PAYMENT: <signed proof>
    S->>Sol: verify settlement
    Sol-->>S: confirmed
    S-->>C: 200 OK + X-PAYMENT-RESPONSE

Loading

Live playground: 402.surfnet.dev.

Quick start

A paid endpoint in seven lines of Ruby. Save as config.ru, bundle exec rackup, and you have a stablecoin paywall.

# config.ru
require "sinatra/base"
require "solana_pay_kit"

class App < Sinatra::Base
  get("/report") do
    require_payment! usd("0.10")
    "premium content"
  end
end

run App

Call it from any HTTP client. Without payment you get a 402; with the pay CLI the wallet pops Touch ID, signs a USDC transfer, and replays the request:

brew install pay   # or: npm install -g @solana/pay

curl     -i http://127.0.0.1:4567/report   # → 402 Payment Required
pay curl -i http://127.0.0.1:4567/report   # → 200 OK + receipt

The same surface is available in nine languages — server-side, client-side, or both:

Language	Server	Client
TypeScript	✅	✅
Rust	✅	✅
Go	✅	✅
Python	✅	✅
Ruby	✅	—
PHP	✅	—
Lua	✅	—
Kotlin	—	✅
Swift	—	✅

Each language directory has its own README with framework-specific snippets (Sinatra/Rails, Express, FastAPI, Axum, Gin, …).

License

MIT