What a strong Next.js specialist actually knows
Next.js is React with opinions about rendering, and the opinions matter. A strong developer knows when a page should be static, server-rendered or streamed, how the App Router changes data fetching, and why a Server Component can remove a whole layer of client code. They treat Core Web Vitals as a requirement, not a late audit.
Beyond rendering, expect solid TypeScript, authentication flows, image and font optimization, middleware and caching rules that do not leave users looking at stale data. Good candidates can explain what runs on the server, what runs in the browser and what that costs in bundle size.