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Use when reviewing scripts, client components, bundles, or runtime behavior related to Prefer immutable data patterns. Inspect both source code and the browser execution path so fixes target the real bottleneck or bug.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Avoid redundant image alternative text. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when reviewing image assets, markup, and CDN or build transforms related to Optimize all images for web. Check encoded size, rendered size, loading strategy, and above-the-fold impact together.

Use when auditing the image pipeline, static assets in `public/`, CMS-managed media, or image CDN transforms. Separate file-size problems from dimension mismatches so you can tell whether the issue is compression, format choice, or responsive delivery.

Use when reviewing image assets, markup, and CDN or build transforms related to Compress images without quality loss. Check encoded size, rendered size, loading strategy, and above-the-fold impact together.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Ensure identical links have consistent destinations. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when auditing URL structures for word separator format, generating slugs from titles, or planning a URL migration from underscores or spaces to hyphens with appropriate redirects.

Use when auditing a site's internal and external links for protocol consistency, migrating a site from HTTP to HTTPS, or reviewing hardcoded URLs in a codebase that may use `http://` instead of `https://`.

Use when auditing whether a website or web application serves content exclusively over HTTPS with a valid certificate.

Use when auditing slow page loads, heavy assets, or rendering delays related to Enable HTTP/2 or HTTP/3. Verify the actual bottleneck in DevTools, Lighthouse, or field data before recommending changes.

Use when checking whether a web server is configured to redirect all HTTP traffic to HTTPS.

Use when auditing slow page loads, heavy assets, or rendering delays related to Minimize HTTP requests. Verify the actual bottleneck in DevTools, Lighthouse, or field data before recommending changes.

Use when reviewing templates, rendered HTML, or shared components related to Use semantic HTML elements. Validate the final browser-facing markup, not just the source framework abstraction.

Use when applies to XHTML documents and polyglot HTML documents that must parse correctly as both HTML5 and XML. For modern HTML5-only documents, only `lang` is needed and `xml:lang` is not required. Check when auditing documents served as application/xhtml+xml or documents that include both attributes.

Use when auditing page weight for crawl efficiency, investigating why certain page content is not appearing in Google's index, or reviewing server-rendered pages that embed large JSON payloads in HTML.

Use when reviewing templates, rendered HTML, or shared components related to Add resource hints (preload, prefetch, dns-prefetch). Validate the final browser-facing markup, not just the source framework abstraction.

Use when reviewing HTTP response headers on any site that serves content over HTTPS.

Use when auditing metadata, crawlability, structured data, or indexability related to Add hreflang tags for multilingual sites. Verify the rendered HTML and HTTP response rather than relying only on source files.

Use when applies to all CSS layout rules. Check `width`, `min-width`, fixed pixel values on containers, `overflow`, `white-space`, and `word-break` properties. Use when auditing responsive design or WCAG 2.1 Level AA compliance. Test at 320px viewport width and at 400% browser zoom.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Maintain logical heading order. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Use logical heading hierarchy. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when reviewing stylesheets or components that use JavaScript to toggle classes on parent elements based on child state, form input values, or content presence — :has() may replace the JavaScript entirely.

Use when auditing slow page loads, heavy assets, or rendering delays related to Optimize Google Tag Manager implementation. Verify the actual bottleneck in DevTools, Lighthouse, or field data before recommending changes.

Use when auditing locally-focused or regionally-targeted pages for geo targeting signals, particularly on sites targeting audiences through Bing or regional search engines. Note that these meta tags have no documented effect on Google's ranking.

Use when auditing content pages for freshness signals, setting up HTTP Last-Modified headers in a web server config, or ensuring Article JSON-LD dateModified is updated when CMS content changes.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Provide titles for iframes and frames. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when reviewing templates, rendered HTML, or shared components related to Validate forms accessibly. Validate the final browser-facing markup, not just the source framework abstraction. Distinguish between browser-posted forms and client-handled React forms so you do not over-report missing `method` or `action` as accessibility defects.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Associate labels with form controls. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when reviewing HTML forms, fetch/XHR calls, and form action attributes to ensure data is submitted exclusively over HTTPS.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Use a single label for each form field. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when reviewing public HTML forms (no authentication required to reach them) for bot and abuse protection mechanisms.

Use when applies to all CSS `font-size` declarations, particularly those using `px` units for body text, UI labels, and navigation. Use when auditing mobile responsiveness and accessibility compliance. Check for `font-size` in media queries targeting small screens.

Use when auditing slow page loads, heavy assets, or rendering delays related to Optimize web font loading. Verify the actual bottleneck in DevTools, Lighthouse, or field data before recommending changes.

Use when reviewing stylesheets, component styles, and responsive behavior related to Provide visible custom focus indicators. Check the rendered layout across breakpoints and interaction states before proposing a fix.

Use when reviewing sticky navigation, consent banners, chat widgets, skip links, or any fixed-position UI. Validate the actual tab order and viewport behavior at realistic zoom levels.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Manage focus during dynamic interactions. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when reviewing stylesheets, component styles, and responsive behavior related to Apply Flexbox best practices. Check the rendered layout across breakpoints and interaction states before proposing a fix.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Prevent seizure-triggering flashing content. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

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

Use when you need to find the 2-3 most popular and well-maintained npm packages relevant to a frontend checklist rule, validate they meet quality thresholds, and add them to the rule's frontmatter.

Use when reviewing image assets, markup, and CDN or build transforms related to Use descriptive image filenames. Check encoded size, rendered size, loading strategy, and above-the-fold impact together.

Use when reviewing templates, rendered HTML, or shared components related to Make file uploads accessible. Validate the final browser-facing markup, not just the source framework abstraction.

Use when optimising Largest Contentful Paint (LCP), reducing render-blocking resource contention, or fine-tuning resource loading order in the critical rendering path.

Use when reviewing templates, rendered HTML, or shared components related to Implement favicons for all devices. Validate the final browser-facing markup, not just the source framework abstraction.

Use when adding FAQ sections to landing pages or blog posts, generating FAQPage JSON-LD from existing Q&A content, or validating that structured data on pages with FAQ sections is syntactically and semantically correct.

Use when auditing content pages for citation quality, suggesting authoritative sources to link for factual claims, or reviewing whether a page's external link attributes (nofollow, noopener) are correctly set.

Use when reviewing scripts, client components, bundles, or runtime behavior related to Use event delegation for dynamic content. Inspect both source code and the browser execution path so fixes target the real bottleneck or bug.

Use when reviewing scripts, client components, bundles, or runtime behavior related to Use ES modules (import/export). Inspect both source code and the browser execution path so fixes target the real bottleneck or bug.

Use when setting up a new project's production observability stack, reviewing incident response readiness, or investigating why errors are going undetected.

Use when reviewing image assets, markup, and CDN or build transforms related to Handle image loading errors gracefully. Check encoded size, rendered size, loading strategy, and above-the-fold impact together.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Fix empty and broken links. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Ensure headings contain text. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when reviewing stylesheets, component styles, and responsive behavior related to Avoid embedded and inline CSS. Check the rendered layout across breakpoints and interaction states before proposing a fix.

Use when reviewing a website for layout and functionality issues caused by adblocker filter rules targeting common ad-related class names and IDs.

Use when auditing a blog, news site, or YMYL content site for trust signals, drafting editorial policy page content, or evaluating whether a site meets Google's quality rater trustworthiness criteria.

Use when auditing slow page loads, heavy assets, or rendering delays related to Remove duplicate JavaScript libraries. Verify the actual bottleneck in DevTools, Lighthouse, or field data before recommending changes.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Use unique IDs for ARIA references. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Use unique IDs for active elements. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when auditing a site's meta tag uniqueness, generating page-specific meta descriptions, or reviewing CMS templates that inject the same description globally.

Use when reviewing templates, rendered HTML, or shared components related to Make drag and drop accessible. Validate the final browser-facing markup, not just the source framework abstraction.