How do I reduce the bundle size of a React app?

Use a bundle analyzer. It shows every dependency and its size, so you can find heavy libraries, accidentally shared chunks, and unused code. Never guess; the analyzer shows exactly what users download.

Code splitting routes with React.lazy. Users only download the code for the page they visit, so the initial bundle stays small and the first load improves significantly, especially on slow networks.

Look for lighter alternatives. date-fns is tree-shakable while moment is huge; lodash has per-method imports while the full bundle is heavy. Choose the lighter option and import only what you use.