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x402 is an open payments protocol built on the HTTP 402 status code that lets an application or agent pay per request in stablecoins without accounts or API keys. Builders add its middleware to a service to charge per call, or to a client so it can pay.

web3-ethereum-defi is a Python library for DeFi integration and data research, with wrappers for Uniswap, Aave, Chainlink, and USDC on top of web3.py. Python builders import it instead of writing those protocol wrappers themselves.

Request Network is a protocol and JavaScript library for creating, paying, and tracking crypto invoices and payment requests onchain. Builders install the client library to add invoicing to their own application.