The fastest way to add pay-per-request to a service is a language-native SDK: server middleware that returns the 402 challenge and verifies payment, plus a client wrapper that lets an agent pay automatically. The ecosystem ships libraries for TypeScript/Node.js (the largest slice), Python (the language of AI), Rust (performance-critical facilitators) and Go (payment middleware and services).
Pick your language below to see every tracked library, ranked by GitHub stars. Most wrap the same x402 handshake, so switching languages rarely means re-learning the flow.
