Creating x402 HTTP Clients (Fetch and Axios)

Build HTTP clients that automatically detect 402 Payment Required responses, sign Algorand transactions, and retry requests with payment proof -- all transparently.

Prerequisites

Before using this skill, ensure:

1. Node.js or browser environment with TypeScript support
2. An Algorand wallet or private key for signing payment transactions
3. USDC balance on the target network (testnet or mainnet) in the payer's account

Core Workflow: The 402 Payment Flow

The key insight is that wrapFetchWithPayment and wrapAxiosWithPayment intercept 402 responses, sign a transaction group, and retry the original request with the payment header -- all automatically: