CosmJS is a versatile, open-source JavaScript library designed to power client solutions across various platforms in the Cosmos ecosystem, from web apps and browser extensions to server-side clients like faucets and scrapers. Developed in TypeScript, this modular monorepo comprises numerous npm packages under the @cosmjs namespace, such as @cosmjs/stargate for Cosmos SDK client interactions and @cosmjs/crypto for blockchain cryptography. Supporting Node.js 14+, modern browsers, and browser extensions, CosmJS emphasizes modularity and a clean dependency tree, allowing users to tailor functionality to their needs. While configured for ES2020 standards and utilizing WebAssembly for cryptographic functions, the library’s webpack settings offer guidance for both modern and prior setups. Active development, thorough API documentation, and community engagement via GitHub and Discord ensure its continual evolution and suitability for sophisticated Web3 applications.