How to Use WebP Images in WordPress (Without a Plugin)

Does WordPress support WebP?

Yes. WordPress has accepted .webp uploads natively since version 5.8 (July 2021) and generates WebP thumbnails for them just like JPEG. Since 6.1 it can even output WebP versions of uploaded JPEGs automatically when the hosting server supports it. If your site refuses WebP uploads, you are either on an old version or your host has disabled the MIME type (see troubleshooting below).

The plugin-free workflow

1. Collect your originals (PNG, JPG, HEIC from your phone).
2. Convert them to WebP with Fast WebP Converter. Use quality 80 for photos and 90 for graphics, and set the maximum width to your theme's content width × 2 (usually 1600–2400 px).
3. Rename files descriptively before upload: blue-linen-shirt-front.webp beats IMG_4821.webp for image SEO.
4. Upload to the Media Library as usual (Media → Add New, or directly in the block editor).
5. Add alt text to every image. It is required for accessibility and used by Google Images.
6. Insert with the Image block, which automatically adds srcset, sizes, loading="lazy" and width/height attributes.

Why convert before upload instead of using a plugin?

• No server load. Optimisation plugins run ImageMagick/GD on your host, which is slow on shared hosting and often times out.
• No monthly fees. Most image plugins charge per image or per month; a one-time $99 PRO licence converts unlimited images forever.
• Control. You decide quality and width per image instead of a global setting.
• Smaller Media Library. Uploading only WebP avoids storing both JPEG and WebP copies of every thumbnail size.

Troubleshooting: 'Sorry, you are not allowed to upload this file type'

This message means your WordPress installation does not recognise image/webp. Check the WordPress version first (update to 5.8+). If it persists, your host or a security plugin restricted MIME types. Add the following to your theme's functions.php or a small custom plugin:

add_filter('upload_mimes', function($mimes) { $mimes['webp'] = 'image/webp'; return $mimes; });

Fallbacks for old browsers

With 97%+ browser support, most sites no longer need fallbacks. If your analytics show meaningful Internet Explorer or very old Safari traffic, keep JPEG versions and use a plugin (Performance Lab, Converter for Media) that outputs <picture> elements. Otherwise, skip the complexity.

Measuring the result

Run PageSpeed Insights(opens in new tab) before and after. Look at Largest Contentful Paint and the 'Serve images in next-gen formats' audit. Sites typically see LCP drop by 0.5–1.5 seconds on mobile after converting their above-the-fold images to WebP.