How we migrated a CSR site to SSR without losing a single ranking

How we migrated a CSR site to SSR without losing a single ranking

Most framework migrations bleed 20-40% organic. This SaaS went CSR React → Next.js SSR and lost 0%. The difference was a boring pre-flight checklist run two weeks early.

— Crawl the live CSR site twice: once as a browser (rendered), once as raw HTML. Diff every title, H1, canonical, meta.
— Export the full URL inventory from Search Console + logs, not just the sitemap. We found 312 ranking URLs missing from the sitemap.
— Map every old route to new: hash routes (/#/pricing) became /pricing with 301s.
— Snapshot rendered HTML of the top 50 pages as the 'must match' baseline.

Launch day, we diffed staging SSR against that baseline byte-by-byte on key tags.

The reveal during QA: the new build dropped self-canonicals on paginated pages — caught before launch, not after.

Result: post-migration organic held at -2% week one → +14% by week six, versus the 30% drop the CFO had budgeted for.