o1js is a TypeScript framework that simplifies the development of applications using zero-knowledge (zk) cryptography, enabling developers to create zk circuits and proofs for browser, Node.js, or the Mina Protocol. It is designed for developers looking to build privacy-preserving applications, zkApps, or integrate zk-SNARKs into their projects without deep cryptographic expertise. The framework is open-source and supported by a growing community with additional libraries and tools available.