The .svelte file extension is used for Svelte component files. Svelte is a modern JavaScript compiler that transforms component code into highly efficient vanilla JavaScript at build time. Unlike traditional JavaScript frameworks that do the bulk of their work in the browser, Svelte shifts that work into a compile step. This results in smaller bundle sizes, faster initial load times, and improved runtime performance. A .svelte file typically contains a combination of HTML markup, JavaScript logic, and CSS styling, all within a single file. The Svelte compiler analyzes these components and generates optimized JavaScript code that directly manipulates the DOM, minimizing the overhead associated with virtual DOM diffing and reconciliation. Svelte components are reactive by default, meaning that changes to data automatically update the corresponding parts of the user interface. This reactivity is achieved through Svelte's compiler, which inserts efficient update logic into the generated code. Svelte files are the building blocks of Svelte applications, allowing developers to create reusable and maintainable UI components.