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Animation Performance

Testing & Quality
animation-performance

Animation Performance is an Agent Skill for testing & quality published in the thedaviddias/Front-End-Checklist repository on GitHub: a SKILL.md instruction file an AI agent can load to do this task.

Use when reviewing stylesheets, component styles, and responsive behavior related to Use transform and opacity for animations. Check the rendered layout across breakpoints and interaction states before proposing a fix.

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How to use this skill

Bring this guide into your coding agent with a prompt tailored to the tool you use.

  1. Open your project in Codex.
  2. Copy and paste the prompt below.
  3. Review files and risks before approving any action.
Prompt to paste
Inspect the Agent Skill at https://github.com/thedaviddias/Front-End-Checklist/blob/HEAD/skills/animation-performance/SKILL.md and all supporting files. Report provenance, permissions, scripts, dependencies, and security risks. Propose an exact installation into .agents/skills/animation-performance, but wait for my approval before writing files or running scripts.

Copying this prompt does not install or run the skill. Review third-party files before use.

Use transform and opacity for animations

Animating layout properties (width, height, top, margin) triggers the full browser rendering pipeline on every frame — style recalculation, layout, paint, and composite. This runs on the main thread and competes with JavaScript. Animating transform and opacity skips layout and paint entirely and runs on a dedicated GPU thread, achieving smooth 60fps even when the main thread is busy.

Quick Reference

  • Only transform and opacity can be composited on the GPU without triggering layout
  • Use will-change: transform sparingly to promote an element to its own compositor layer
  • Prefer CSS transitions and animations over JavaScript animation libraries for simple effects
  • Respect prefers-reduced-motion to disable animations for users who need it

Check

Find CSS animations or transitions in this file that animate layout-triggering properties like top, left, width, height, or margin. Flag them for optimization.

Fix

Convert layout-triggering animations to use transform equivalents: position changes to translate(), size changes to scale().

Explain

Explain the browser rendering pipeline, why transform and opacity are performant for animation, and how the GPU compositor works.

Code Review

Review stylesheets, component styles, and responsive states related to Use transform and opacity for animations. Flag exact selectors, declarations, or breakpoints that violate the rule in the rendered UI.

For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/en/rules/css/animation-performance