hydration-guardian

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Ensures zero-mismatch integrity between server-rendered HTML and client-side React trees. Use when debugging hydration errors, fixing text content mismatches, handling browser extension DOM pollution, implementing selective hydration with Suspense, using the React 19 use() hook for deterministic server-to-client data bridges, or applying Next.js use cache for data drift prevention. Use for hydration mismatch, SSR, hydrateRoot, suppressHydrationWarning, onRecoverableError, two-pass rendering.

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Sourceoakoss/agent-skills

Added on2026-02-25

NPX Install

npx skill4agent add oakoss/agent-skills hydration-guardian

SKILL.md Content

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Hydration Guardian

Overview

Ensures zero-mismatch integrity between server-rendered HTML and client-side React trees. Covers hydration error diagnosis, selective hydration via Suspense boundaries, deterministic data bridges with the React 19

use()

hook,

'use cache'

for eliminating data drift, two-pass rendering for client-only content, React 19's single-diff hydration error reporting for pinpointing exact mismatches, and automated validation of rendered DOM state.

When to use: Debugging hydration mismatch errors, fixing text content mismatches, handling browser extension DOM pollution, implementing deterministic data bridges, optimizing SSR/client hydration performance, setting up error monitoring with

onRecoverableError

.

When NOT to use: Client-only React applications without SSR, static sites without hydration, API-only backends.

Quick Reference

Pattern	Approach	Key Points
Selective hydration	`<Suspense fallback={...}>` boundary	Hydrates independently; prioritizes user interaction
Deterministic bridge	`use(serverPromise)` instead of useEffect	Direct server-to-client data transition (React 19)
Cache directive	`'use cache'` in data fetchers	Share exact server result with client during hydration
Two-pass rendering	`useState` + `useEffect` for client-only	First render matches server; second adds client content
Client-only skip	`next/dynamic` with `ssr: false`	Exclude component from server render entirely
Error monitoring	`onRecoverableError` on `hydrateRoot`	Detect and report silent hydration recovery
Error reporting	React 19 single-diff error format	Pinpoints exact mismatch location with unified diff output
Error callbacks	`onUncaughtError` , `onCaughtError`	Granular error handling on `createRoot` / `hydrateRoot`
Date/time safety	UTC normalization or server-synced context	Prevent locale-dependent hydration mismatches
Extension resilience	Test with common browser extensions active	Detect DOM pollution from translators, dark-mode tools

Hydration Error Diagnosis

Error Message	Likely Cause	Corrective Action
`Text content did not match`	Non-deterministic render (dates, random values)	Use two-pass rendering or `suppressHydrationWarning`
`Expected server HTML to contain`	Client renders content server did not	Move client-only code to `useEffect` or dynamic import
`Hydration failed`	Invalid HTML nesting ( `<p>` inside `<p>` )	Fix HTML structure; browsers auto-correct causing drift
`Extra attributes from server`	Server-only attributes not on client	Ensure attribute parity or use `suppressHydrationWarning`
`There was an error while hydrating`	Extension-modified DOM or major mismatch	Check for browser extensions; verify HTML validity

Common Mistakes

Mistake	Correct Pattern
Using `suppressHydrationWarning` on container elements	Fix the root cause; suppress only on leaf elements with unavoidable differences
Accessing `window` or `document` in the render body	Wrap client-only code in `useEffect` or use `next/dynamic` with `ssr: false`
Using `Math.random()` or `new Date()` without stable seeds	Use UTC normalization, server-cached values, or two-pass rendering
Ignoring silent hydration recovery in production	Configure `onRecoverableError` on `hydrateRoot` to log and monitor
Using `dangerouslySetInnerHTML` with server/client mismatch	Ensure identical content or use a dedicated `key` change to force remount
Checking `typeof window !== 'undefined'` in render	Use two-pass rendering; the check runs on server too (it returns false)
Nesting `<p>` inside `<p>` or `<div>` inside `<p>`	Fix invalid HTML nesting; browsers correct it causing server/client drift

Delegation

Scan rendered pages for hidden hydration warnings: Use
```
Explore
```
agent with Chrome DevTools to run the hydration audit script
Fix hydration mismatches across multiple routes: Use
```
Task
```
agent to isolate, correct, and verify each affected component
Design hydration-safe architecture for new features: Use
```
Plan
```
agent to select between Suspense boundaries, two-pass rendering, and cache patterns

References

Common Mismatches -- causes, diagnosis, and fixes for hydration mismatch errors including dates, locales, HTML nesting, and browser extensions
Selective Hydration -- Suspense-based selective hydration, streaming SSR, two-pass rendering, and client-only components
Use Cache Patterns -- data drift prevention, Next.js use cache directive, React 19 use() hook, deterministic data bridges
Validation Techniques -- automated DOM verification, mutation monitoring, onRecoverableError, and production hydration monitoring