Auto-Convert Every WordPress Upload to WebP (Free, No Cloud Service)

If you have ever run a Lighthouse audit on a content-heavy WordPress site, you know the usual verdict: "Serve images in next-gen formats." Translation: your JPEGs and PNGs are too heavy, and WebP would cut them down a lot. The problem is that nobody wants to convert images by hand, and most automated options either run as a bulk job you have to remember to trigger, or push your images to a cloud service with a monthly quota. I wanted something simpler: upload an image, get a WebP, done. So I built a free plugin called Pixellize Image Optimizer , and this post walks through the problem, how the plugin solves it, and how it works under the hood. Why WebP is worth it WebP files are usually 25 to 35 percent smaller than the equivalent JPG or PNG at the same visual quality. On an image-heavy page that is a real difference: Faster Largest Contentful Paint, which is one of the Core Web Vitals Google uses for ranking. Less bandwidth, which matters if you pay for CDN traffic. No visible quality loss at sensible quality settings. Browser support is no longer a concern. Every current browser handles WebP. The approach: convert on your own server, on upload Instead of a cloud API, the plugin converts images locally with the PHP GD or Imagick extension (almost every host has one). There is no account, no API key, and no paid tier. The core flow: You upload an image to the Media Library as usual. The plugin generates a WebP version of the full image and every thumbnail size. Your front end serves the WebP automatically. How it works under the hood For WordPress developers, here is the interesting part. The plugin hooks into the standard upload and rendering pipeline rather than fighting it: On upload, it taps into the attachment metadata generation so it can convert the full image and every registered sub-size, not just the original. That matters because responsive images use srcset , and a half-converted set defeats the purpose. On the front end, it rewrites image URLs to the We