Audit slow page loads by measuring LCP, the time until the largest visible content appears. Identify bottlenecks in images, server responses, and rendering, then recommend changes supported by measurements.
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.
largest-contentful-paint examines LCP, the time it takes for the largest content on a page to appear, and helps improve slow loading. It checks image formats and sizes, preloading of critical resources, and server response times. Suggested changes follow the causes identified through measurement. During code reviews, it points to specific files, requests, or rendering steps that add unnecessary work.
Use it to investigate pages where the main image or primary content appears slowly. Measurement results also help you decide whether to start with image delivery or server response times. The improvement target is an LCP below 2.5 seconds, giving the review a concrete timing goal.
Before recommending changes, confirm the cause using DevTools, Lighthouse, PageSpeed Insights, or data from real usage environments. Recommendations must follow those findings; image preloading and CDN use should not be suggested as blanket changes without measurement.
This overview was written by AI (OpenAI Codex) from the public SKILL.md. Check the original below for the exact behavior.
AI rated this skill on four points using only the contents of its SKILL.md. Stars and popularity are not taken into account.
The total counts each point as A = 25, B = 15, C = 5. Rated by AI (OpenAI Codex) as of Oct 23, 2026. Treat it as a guide and read the original before installing.
Review the instructions the agent will receive before you install.
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.
Measure LCP using Lighthouse or PageSpeed Insights. Verify the largest visible element renders within 2.5 seconds.
Optimize LCP by preloading critical resources, optimizing images, using CDN, and reducing server response time.
Explain how LCP measures perceived load speed by tracking when the largest visible content element becomes visible.
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/rules/performance/largest-contentful-paint
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Create and review custom 404 pages that help visitors recover from broken or moved links through search and navigation. Check the rendered page and HTTP response so missing content returns a proper 404 status.
Audit or create a dedicated About page that explains a website’s purpose and identifies its people or organization. Review the rendered output and supporting information, including expertise and contact details, to find gaps.
Review and add automated accessibility checks for components, pages, and continuous integration workflows. Use axe-based tools to detect structural and attribute issues, while identifying checks that still need keyboard or screen reader testing.
Review sign-in, registration, multi-factor authentication, and account recovery for accessibility barriers. Find blocked paste, difficult code entry, and inaccessible backup methods, then suggest authentication paths that support password managers, autofill, or device approval.
Review form errors, success messages, and live updates so screen reader users receive important notifications. Check the HTML delivered to the browser, announcement settings, display duration, and dismissal controls, then identify specific elements that need changes.
Review HTML tables so screen reader users can understand how headers and data relate. Check header markup, table descriptions, and merged cells, then identify specific fixes and ways to verify them.