If you are a frontend developer and you are using TypeScript, you have probably asked yourself: "Should I use type or interface?" At first they look exactly same. They both help you define how you want an object to look so your code doesn't crash. But as your React or Next.js project gets bigger, those small differences start to matter, performance and clean coding. I will explain these differences in this article so you can choose which one to use in less than 5 minutes 1. The Quick Comparison At their core, both tools act as a "contract" for your data. Here is how they look side-by-side: Feature Interface Type Alias Declaration interface User { name: string; } type User = { name: string; }; Best For Objects and Classes Unions, Tuples, and Primitives Merging Automatically merges same names Throws an error for same names Performance Faster (uses internal caching) Slightly slower (recomputes) 2.…