What Hydration means
Hydration lets a page appear quickly and then become interactive. Heavy hydration can make a page look ready while buttons still feel sluggish, which shows up in INP scores. Good engineering keeps it light.
Why it matters for your website
Hydration lets a site show content fast from server-rendered HTML and then become interactive. If it is slow or heavy, buttons can look ready but not respond, which frustrates visitors and can hurt your INP score. Lighter hydration often means a faster, more usable site.
Example
On a Next.js ecommerce site, product pages appear quickly, but the Add to Cart button does nothing for a moment until hydration finishes. Trimming unneeded JavaScript shortens that gap.
Tips
- Ship less JavaScript so hydration finishes sooner.
- Only make interactive the parts of a page that need it.
- Test on a mid-range phone, where hydration delays show up most.
Common mistakes
- Rendering different content on server and client, which causes hydration errors.
- Turning static content into interactive components for no reason.
Questions about Hydration
What is Hydration?
The step where JavaScript attaches interactivity to HTML that was already rendered on the server.
What is a hydration error?
It happens when the HTML from the server does not match what JavaScript builds in the browser. It can cause flicker, broken features or warnings in the console.
Does hydration affect SEO?
Search engines see the server-rendered HTML, which helps. Slow hydration mostly affects user experience and responsiveness metrics.
