This was originally published on rollgate.io/blog/feature-flags-nextjs . Why Feature Flags in Next.js? Next.js is not a typical React app. With the App Router, your code runs in multiple environments — the server, the edge, and the browser — sometimes in the same request. This makes feature flags both more powerful and more complex than in a single-page application. Here is why feature flags matter specifically for Next.js: Server-Side Rendering creates a decision point. When a Server Component renders on the server, you need the flag value before sending HTML to the client. If you evaluate flags only on the client, users see a flash of the wrong content (or a loading spinner) before the correct variant appears. Edge Middleware runs before rendering. Next.js middleware can redirect or rewrite requests at the edge, before any component renders. This is the ideal place for A/B testing entire pages — route users to /pricing-a or /pricing-b based on a flag, with zero layout shift.…