SSR vs SSG vs CSR — when to use each?

CSR ships JS and renders in the browser (best for app-like, auth'd UI). SSR renders per request on the server (best for personalized, fresh content). SSG pre-renders at build time (best for marketing/blogs). ISR adds incremental revalidation on top of SSG.

7 min read·~15 min to think through

Four common strategies, each trading freshness for cost and TTFB for HTML readiness:

CSR (Client-Side Rendering) — server returns a near-empty HTML shell; JS hydrates and renders. Pros: simple infra, app-like UX. Cons: slow LCP, bad SEO without extra effort.
SSR (Server-Side Rendering, per request) — server renders to HTML on every request. Pros: fast meaningful paint, fresh data, SEO-friendly. Cons: server cost, slower TTFB than static, requires running infra.
SSG (Static Site Generation, build time) — render once at build, serve from CDN. Pros: cheap, instant TTFB, infinitely scalable. Cons: data is build-time stale; rebuild cost grows with page count.
ISR / Revalidation — SSG + a stale-while-revalidate window. Best of both for content that changes occasionally (blogs, product pages).

Decision heuristic:

Marketing / docs / blog → SSG (or ISR if frequent updates).
E-commerce product page → ISR (cheap, mostly fresh).
Logged-in dashboard → CSR for the app shell + server-data per route. RSCs (React Server Components) blur the lines further.
Personalized SSR → only when SEO + per-user freshness both matter (e.g., logged-in homepage that's also indexed).

Modern Next.js / Remix lets you pick per route. Don't pick one strategy for the whole app — pick per page based on what that page actually needs.

Code

Follow-up questions

•How do React Server Components change the SSR vs CSR conversation?
•What's the cost model of SSR at scale and how do you cap it?
•When does PPR (Partial Prerendering) make sense?

Common mistakes

•Using CSR for content pages and tanking SEO + LCP.
•Using SSR everywhere and paying for compute on pages that could be static.
•Treating ISR cache as fresh — there's always a stale window.

Performance considerations

•SSG/ISR served from CDN edge ≈ <50ms TTFB. SSR is bound by your origin region.
•CSR's LCP is gated by JS download + parse + render — every KB matters.

Edge cases

•Cookies/personalization break CDN caching — opt out with `cache: 'no-store'` or per-user keys.
•ISR's stale window can show outdated data for that first request after invalidation; design copy that tolerates it.

Real-world examples

•Vercel/Next docs: SSG. Linear web app: CSR shell + RSC for data. Amazon product page: ISR-like edge cache + SSR for personalized blocks.

Senior engineer discussion

Senior signal: discuss the cache hierarchy (browser, edge, ISR, ORM), per-route cost modeling, RSC streaming, and partial prerendering as the future hybrid.