Coi is a new programming language designed for building reactive web applications, prioritizing type safety, performance, and compact bundle sizes. It compiles to WebAssembly, which means applications run with near-native speed. In benchmarks, Coi's bundle size is significantly smaller than popular frameworks: 40% smaller than Svelte, 72% smaller than Vue, and 88% smaller than React. This leads to faster downloads and improved user experiences, especially on mobile devices. Coi's architecture emphasizes fine-grained reactivity without the overhead of a virtual DOM. Instead of using a virtual tree to manage updates, Coi generates direct DOM manipulations, which helps maintain 60fps animations and responsive interactions. The language incorporates strict typing, allowing developers to catch errors at compile time rather than runtime. Key features include component-based design, direct DOM and CSS integration, and various control flow tags for easier conditional rendering. The setup process is straightforward, requiring Clang 16 or greater and a few simple commands to get a project up and running. With a focus on computation-heavy applications, Coi is well-suited for simulations, gaming, and data processing. The roadmap hints at future support for native platforms and server-side applications, expanding its usability beyond just web development. The community also provides resources, including documentation and editor support for popular coding environments like VS Code and Sublime Text.