Modern search engines can execute JavaScript, but rendering is expensive and delayed. Content that only appears after client-side hydration can be missed, delayed in indexing, or ranked lower than equivalent server-rendered content.
Best practices
- Server-render or statically generate primary content whenever possible.
- Avoid hiding critical text behind user interaction.
- Test with Google's URL Inspection tool to confirm what Google actually sees.
- Do not block JavaScript resources in robots.txt.
Example
A React SPA that ships an empty shell and hydrates a product feed client-side is indexed with just the shell content. Switching to Next.js server components restores full indexing within a week.
How SEM Optimiser reports it
The audit compares the initial HTML response with the rendered DOM and flags pages where important content only appears after hydration.
Related terms
- Rendering Budget
Rendering budget is the compute and time Googlebot allocates to executing JavaScript on a URL before falling back to the un-rendered HTML.
- Crawl Budget
Crawl budget is the number of URLs Googlebot can and will crawl on a website within a given time frame, determined by crawl capacity and crawl demand.
- Index Coverage
Index coverage is the report in Google Search Console that shows which URLs on a site are indexed, which are excluded, and why.