Server-side rendering
Generating a page's full HTML on the server for each request, so crawlers and users receive complete markup without executing JavaScript.
TechnicalRehydration
Hydration
Attaching client-side JavaScript behaviour to server-rendered HTML so a static page becomes interactive.
In full
Hydration is the point where SSR's fast paint meets the cost of shipping and executing the framework, and it is a common cause of poor INP: the page looks ready but does not respond until hydration finishes. Techniques such as partial, progressive, islands and selective hydration reduce this by hydrating only interactive regions. A hydration mismatch, where client output differs from server HTML, can also cause content to be replaced after render.
Example
A 400 KB bundle blocks the main thread for 900 ms after paint, so early taps on the menu do nothing and INP measures over 500 ms.
Related terms
Interaction to Next Paint
A Core Web Vital measuring overall responsiveness as the latency of the worst (approximately) interaction on a page; good is 200 ms or…
Single-page application
An architecture where one HTML shell loads and JavaScript handles all subsequent routing and content updates without full page loads.
JavaScript rendering
The execution of a page's client-side JavaScript by a search engine so that content and links generated at runtime become indexable.
Progressive enhancement
A build strategy that starts with working HTML and layers on CSS and JavaScript, so core content and navigation function without scripts.