# Hydration

Canonical HTML: /atlas/hydration
Atlas version: atlas-2026-07-28-v1
Category: Rendering and client execution

## Definition

Hydration attaches client behavior to HTML that was already rendered on the server.

## How it works

When implemented well, the response contains meaningful content and crawlable links while JavaScript adds interactivity without replacing the document’s semantic core.

## How to validate it

Disable JavaScript and verify that the page remains readable and navigable, then detect whether hydration unexpectedly removes or rewrites canonical elements.

## Common failure

Hydration mismatches can replace correct server markup with an error, duplicate content, or a different link graph.

## Related topics

- [Server-rendered content](/atlas/server-rendering)
- [Progressive enhancement](/atlas/progressive-enhancement)