Review website images for file format, size, dimensions, and loading behavior. Produce improved HTML with image variants for different screen sizes, suitable compression, and deferred loading where appropriate, while addressing loading speed and layout shifts.
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.
Review the instructions the agent will receive before you install.
Images typically account for 50%+ of page weight. Unoptimized images cause slow load times, wasted bandwidth, poor Core Web Vitals scores, and frustrated users—especially on mobile networks.
<picture> element for format fallbacksScan this codebase for all image assets and <img> elements. For each image, verify: 1) Format is appropriate (WebP/AVIF for photos, SVG for icons, PNG only for transparency). 2) Responsive srcset and sizes attributes exist for images > 100px wide. 3) width/height attributes are present to prevent layout shift. 4) loading='lazy' is set for below-fold images. 5) File sizes are reasonable (< 200KB for photos, < 50KB for graphics). Report issues grouped by severity with file paths.
For each image optimization issue found: 1) Convert JPEG/PNG photos to WebP with AVIF fallback using <picture> element. 2) Add srcset with 400w, 800w, 1200w, 1600w variants and appropriate sizes attribute. 3) Add explicit width/height attributes matching aspect ratio. 4) Add loading='lazy' to images below the fold, keep priority images without lazy loading. 5) Compress images to 80% quality for photos, 60% for AVIF. 6) Use SVG for icons and logos. Show the corrected HTML with optimized image markup.
Explain the impact of image optimization on Core Web Vitals, specifically how unoptimized images affect Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS). Cover the compression differences between AVIF, WebP, and JPEG formats, when to use each, and browser support considerations. Describe how srcset and sizes work together to serve appropriately-sized images, and why width/height attributes prevent layout shift. Include bandwidth savings calculations and loading performance improvements.
Review image assets, markup, and delivery configuration related to Optimize all images for web. 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/image-optimization
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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.