Use when reviewing image assets, markup, and CDN or build transforms related to Use modern image formats (WebP, AVIF). Check encoded size, rendered size, loading strategy, and above-the-fold impact together.
インストールする前に、エージェントに与えられる指示の中身を確認できます。
Images are typically 50%+ of page weight. Switching from JPEG to WebP alone reduces transfer sizes by 25-35% with no visible quality change, directly improving Largest Contentful Paint (LCP) and saving bandwidth for users on mobile data plans. These savings compound across every visitor and every image on the site.
<picture> with <source type="image/avif"> and <source type="image/webp"> plus an <img> fallbackScan all <img> elements and CSS background-image declarations in this codebase. Identify: 1) Any <img src> pointing to .jpg, .jpeg, or .png files (not served via a CDN that auto-negotiates format). 2) Any <picture> elements that lack <source type="image/webp"> or <source type="image/avif"> entries. 3) Any CSS background images using JPEG or PNG when a WebP equivalent could be used. Report each finding with file path and line number.
For each image not using modern formats: 1) Convert to WebP at 80% quality using Squoosh or Sharp. 2) Optionally also generate AVIF at 60% quality for browsers that support it. 3) Wrap the original <img> in a <picture> element and add <source type="image/avif"> and <source type="image/webp"> entries with the new files. 4) Keep the original JPEG/PNG as the <img src> fallback. For CSS background images, use a @supports (background-image: url('.webp')) { } query to serve WebP to supporting browsers.
Explain the compression advantages of WebP and AVIF over JPEG and PNG. According to web.dev, WebP lossless images are 26% smaller than PNG and WebP lossy images are 25-35% smaller than JPEG at equivalent visual quality. AVIF offers further improvements: roughly 40-50% smaller than equivalent JPEG. Explain browser support: WebP has 97%+ global browser support as of 2024. AVIF is supported in Chrome 85+, Firefox 93+, and Safari 16.4+. The <picture> element with fallbacks means there is no risk in adopting these formats today.
Review image assets, markup, and delivery configuration related to Use modern image formats (WebP, AVIF). Flag exact files or components where format choice, sizing, or loading behavior violates the rule, and describe how to confirm the fix in DevTools.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/rules/images/modern-format
まだレビューはありません。使ってみた感想をお寄せください。
概要と使いどころ
Use when reviewing templates, rendered HTML, or shared components related to Create a custom 404 error page. Validate the final browser-facing markup, not just the source framework abstraction.
日本語の概要は準備中です。原文の説明を表示しています。
Use when auditing metadata, crawlability, structured data, or indexability related to Create a dedicated About page. Verify the rendered HTML and HTTP response rather than relying only on source files.
日本語の概要は準備中です。原文の説明を表示しています。
Use when reviewing component libraries, page flows, or CI pipelines that need repeatable accessibility checks. Automated testing is strongest at catching structural and attribute-level issues; it does not replace keyboard, screen reader, and manual UX testing.
日本語の概要は準備中です。原文の説明を表示しています。
Use when reviewing sign-in, sign-up, MFA, CAPTCHA, recovery, and re-auth flows. Evaluate the full authentication path, including error handling and backup methods, not just the primary login form.
日本語の概要は準備中です。原文の説明を表示しています。
Use when reviewing templates, rendered HTML, or shared components related to Make notifications accessible. Validate the final browser-facing markup, not just the source framework abstraction.
日本語の概要は準備中です。原文の説明を表示しています。
Use when reviewing rendered HTML, interactive components, or design-system patterns related to Use semantic table markup for screen readers. Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output where relevant.
日本語の概要は準備中です。原文の説明を表示しています。