WordPress performance checks for images and fonts in Shadow
How images and web fonts are sized, compressed, lazy-loaded and served, including modern formats, responsive images and the layout shift caused by missing dimensions.
There are 9 checks on this page. Shadow reports what it finds, and nothing is changed until you approve a fix.
In this family
- Extra Image Sizes Trimmed
- Font Loading
- Image Compression Pipeline Active
- Image Dimensions Not Set Causing Layout Shift
- Image Lazy Loading
- JPEG Quality
- Media Scaling Threshold
- Modern Image Format Support
- Responsive Images Enabled
What each check looks at
Extra Image Sizes Trimmed
Checks whether too many image sizes are registered, causing WordPress to generate excessive file variants on every image upload and waste disk space on unused crops.
Font Loading
Checks whether web fonts are loaded with an optimal font-display strategy and whether external font dependencies are managed to avoid render-blocking requests.
Why it matters. Checks whether fonts are loaded optimally using font-display strategies and whether external font dependencies are reduced via local hosting.
Image Compression Pipeline Active
No image compression plugin is active. Unoptimised images are typically the largest contributor to slow page load times.
Why it matters. Checks whether an automatic image compression/optimisation plugin is active, ensuring uploaded images are compressed to reduce storage and page weight.
Image Dimensions Not Set Causing Layout Shift
Checks whether img tags served by the site include explicit width and height attributes. When dimensions are absent the browser cannot reserve the correct space before the image loads, causing content to shift downward on the page and degrading Cumulative Layout Shift (CLS), a Core Web Vital that affects search ranking.
Why it matters. Flags images without width/height (or a CSS aspect-ratio), which cause Cumulative Layout Shift (CLS) as content jumps down while images load, a Core Web Vitals problem and a reading-experience one.
Image Lazy Loading
Checks that WordPress native image lazy loading has not been disabled, ensuring off-screen images are deferred to improve initial page load performance.
JPEG Quality
Checks whether the WordPress JPEG image quality setting is within the optimal 60-85 range that balances visual quality with manageable file sizes.
Why it matters. Checks the effective JPEG quality level applied by WordPress during image processing, flagging values that are too high (wasteful) or too low (blurry).
Media Scaling Threshold
Checks whether the WordPress big-image-size threshold is disabled, which causes full-resolution uploads to be stored and potentially served without downscaling.
Modern Image Format Support
Checks whether the server supports WebP image format via GD or ImageMagick, enabling WordPress 5.8+ to generate smaller next-generation image files during uploads.
Responsive Images Enabled
Checks whether WordPress responsive image srcset generation is functioning so browsers can load appropriately sized images for each device and viewport.
Why it matters. Verifies that WordPress is generating srcset and sizes attributes for uploaded images, enabling browsers to request appropriately-sized assets.
The other check families
- All performance checks (63)
- Accessibility (12)
- Code quality (7)
- Database (12)
- Design (17)
- Monitoring (10)
- Security (46)
- SEO (28)
- Settings (29)
- Health and workflows (7)
Shadow is free and runs on your own server, with no account. The source is on GitHub, and these descriptions come from it.