What is Crumb?

Crumb is a payment platform for the agentic internet — a full-stack system that lets AI agents, applications, and humans pay for API resources using USDC stablecoins. Built on Circle's Gateway nanopayments and the x402 HTTP payment protocol, Crumb makes payments gasless, automatic, and sub-cent.

The problem

APIs are the backbone of modern software, but paying for them is stuck in the past. Credit cards don't work for machines. API keys with monthly billing don't work when an agent needs to discover and pay for a new resource on the fly. There's no native way for software to pay for software.

The solution

Crumb extends HTTP with a native payment layer. When a client requests a paid resource, the server responds with HTTP 402 Payment Required — a status code that's been reserved since 1997 but never had a standard implementation. The client signs a payment, attaches it to the request, and gets the data back. All in one round-trip.

Agent  →  POST /search                        →  Provider
Agent  ←  402 Payment Required (price: $0.001) ←  Provider
Agent  →  POST /search + signed payment        →  Provider
Agent  ←  200 OK + data                        ←  Provider

No API keys. No monthly invoices. No credit cards. Just HTTP with money.

The platform

Crumb is more than an SDK — it's a full payment platform:

Component	What it does
Crumb App	Web app with wallets, payment handles (@username), QR payments, merchant dashboard
crumb-alpha-sdk	TypeScript SDK for agents (buyers) and providers (sellers)
crumb-alpha-cli	Command-line tool for wallet management and testing
Demo Store	Live merchant store for testing agent payments
Checkout Widget	Embeddable "Pay with Crumb" button for any website
Marketplace	Directory of listed merchants and their API endpoints

Key properties

• Gasless — Circle Gateway batches settlements on-chain. No ETH needed, no gas fees per call.
• Sub-cent — Providers can charge as little as $0.001 per request. Real micropayments.
• Automatic — crumb.fetch(url) handles the entire payment flow in one call.
• Open — Built on x402, an open protocol. Any server can paywall. Any client can pay.
• Multi-chain — Deposit on Arc Testnet, withdraw to Base, Ethereum, Avalanche, Solana, Polygon, Arbitrum, and more.