Front-End-Checklist

Use when reviewing rendered HTML, interactive components, or design-system patterns related to Support content reflow at 400% zoom. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.

Use when applies to any site in health, medicine, finance, law, safety, news, or similar fields. Use when auditing content quality for sites in YMYL categories or investigating why high-quality-seeming content underperforms.

Use when reviewing HTTP response headers for clickjacking protection on any web application with authenticated user actions.

Use when auditing HTTP response headers on any web server or CDN for security hardening.

Use when applies to key landing pages, blog posts, product pages, and any page targeting competitive queries. Use when diagnosing poor rankings or after a Google Helpful Content update.

Use when applies to sites with internal site search functionality. Use when optimizing branded search result appearance or adding structured data for the first time.

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

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

Use when reviewing stylesheets, component styles, and responsive behavior related to Optimize web font formats. Check the rendered layout across breakpoints and interaction states before proposing a fix.

Use when reviewing scripts, client components, bundles, or runtime behavior related to Use Web Storage API safely. Inspect both source code and the browser execution path so fixes target the real bottleneck or bug.

Use when reviewing templates, rendered HTML, or shared components related to Link a Web App Manifest for installability. Validate the final browser-facing markup, not just the source framework abstraction.

Use when applies to any site with more than 20 pages. Use when auditing site architecture, investigating why certain pages underperform in search, or after a site migration.

Use when reviewing templates, rendered HTML, or shared components related to Validate HTML against W3C standards. Validate the final browser-facing markup, not just the source framework abstraction.

Use when reviewing CI coverage, automated checks, or test strategy related to Use visual regression testing. Focus on whether the rule is continuously verified, not just documented.

Use when reviewing templates, rendered HTML, or shared components related to Set the responsive viewport meta tag. Validate the final browser-facing markup, not just the source framework abstraction.

Use when applies to any `<meta name='viewport'>` element in HTML documents. Check the `content` attribute for `user-scalable=no`, `user-scalable=0`, `maximum-scale=1`, or `maximum-scale` values less than 2. This is a common mistake in mobile-first templates and CSS frameworks.

Use when adding page transition animations, image expand/contract effects, shared-element transitions, or improving navigation UX in a single-page or multi-page application.

Use when applies to any page embedding or hosting video content (YouTube, Vimeo, self-hosted). Use when adding video content to a site or auditing structured data coverage.

Use when applies to all `<video>` elements in HTML. The `poster` attribute specifies the URL of an image to show as a placeholder before the video is loaded or played. This is distinct from captions or audio descriptions, which are accessibility requirements. The poster is primarily a UX and performance enhancement, though the lack of a poster can indirectly create a CLS (Cumulative Layout Shift) issue if video dimensions are not declared.

Use when applies to all `<video>` elements and third-party video embeds (YouTube, Vimeo) where the page owner controls the content. Prerecorded videos require `.vtt` caption files via `<track>`. For videos embedded via `<iframe>`, check that the video platform captions are enabled. Audio-only content requires transcripts instead (SC 1.2.1). Video-only content (no audio) requires a text alternative or audio description instead (SC 1.2.3).

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

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

Use when reviewing CI coverage, automated checks, or test strategy related to Write unit tests. Focus on whether the rule is continuously verified, not just documented.

Use when reviewing templates, rendered HTML, or shared components related to Ensure all IDs are unique. Validate the final browser-facing markup, not just the source framework abstraction.

Use when setting up a new TypeScript project, auditing an existing tsconfig.json, or reviewing code where null-reference errors or implicit any types are present.