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largest-contentful-paint

Testing & Quality
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Use when auditing slow page loads, heavy assets, or rendering delays related to Optimize largest contentful paint. Verify the actual bottleneck in DevTools, Lighthouse, or field data before recommending changes.

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How to use this skill

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  1. Open your project in Codex.
  2. Copy the prompt below and paste it into your agent.
  3. Review the proposed files and risks before you approve installation.
Prompt to paste
I want to install this Agent Skill for this project in Codex.

Source SKILL.md: https://github.com/thedaviddias/Front-End-Checklist/blob/HEAD/skills/largest-contentful-paint/SKILL.md

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First, summarize what it does, its dependencies, license status if identifiable, and any risks. Show the exact files you propose to add under .agents/skills/largest-contentful-paint/. Do not write files or run scripts until I approve.

After I approve, install the complete skill folder, including required referenced files, into that project location. Verify it is discoverable, then tell me its actual invocation name and how to use it. Do not claim it is installed until you have verified it.

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

Optimize largest contentful paint

LCP is the most important Core Web Vital for perceived load speed—it measures when the main content becomes visible, directly impacting user perception and SEO rankings.

Quick Reference

  • LCP measures when the largest element renders—target under 2.5s
  • Use preload for hero images and critical resources
  • Optimize image formats and use responsive sizes
  • Reduce server response time (TTFB)

Check

Measure LCP using Lighthouse or PageSpeed Insights. Verify the largest visible element renders within 2.5 seconds.

Fix

Optimize LCP by preloading critical resources, optimizing images, using CDN, and reducing server response time.

Explain

Explain how LCP measures perceived load speed by tracking when the largest visible content element becomes visible.

Code Review

Review the routes, assets, and loading behavior that affect Optimize largest contentful paint. Flag exact files, requests, or rendering steps that add unnecessary network, CPU, or layout cost, and describe the measurement method used to confirm the issue.

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

Rule page: https://frontendchecklist.io/en/rules/performance/largest-contentful-paint