If your site feels a little slower in the first minutes after turning on Image Optimization, that's expected and temporary. You're seeing the cache warm up. Once it's warm, your pages are lighter and faster than before. Here's what's happening and how to confirm it settles.
Why the first views are slower
The first time each image is requested after you enable optimization (or after a purge), we build the optimized version on the fly and then cache it on the CDN. That very first build adds a moment of work, so the earliest views of each image are slightly slower. Every visit after that is served the cached, optimized copy instantly.
So the slowdown you might notice is the cache warming up, and it's brief. It clears itself as pages are visited over the following minutes.
What helps
- Give it a few minutes of normal traffic. As real visitors (and your own browsing) load pages, images build and cache. The warm-up window closes on its own.
- Don't purge repeatedly. Each Purge CDN Cache restarts the warm-up by clearing every cached copy. Purge once when you need to, then let it re-cache. See Purging the CDN cache.
- Test after warm-up, not during. Reload a page a second time. The second load reflects the optimized, cached experience your visitors get.
After warm-up, pages should be faster
Once cached, optimized images are significantly smaller than the originals, so pages transfer less data and load faster, especially on mobile and slower connections. That's the steady state.
Note: On a small number of images that are already tiny or very simple (like a flat-color logo), the optimized version can come out a similar size to the original. Your overall pages are still lighter. If one specific image ends up larger than you'd like, you can exclude it. See Excluding images from optimization.
If it's still slow well after warm-up
Image Optimization runs on our CDN network, not on your WordPress server, so it never adds load to your hosting. If your site is still slow long after the warm-up window, the cause is almost certainly elsewhere. To confirm, use the fast on/off test:
- Set Enable Image Optimization to No and click Save Settings.
- Reload the site in a fresh incognito window.
If it's still slow with optimization off, look to your host, page cache, or another plugin. Our general troubleshooting is the place to start. If turning it off clearly fixes speed and turning it on clearly hurts it even after warm-up, contact us. That's not expected and we'd like to look.
How can I measure the difference?
Visit the front end, right-click an image, and choose Inspect. In the Network panel, reload and click an image request. Compare the transferred Size and the Content-Type (image/avif or image/webp means the smaller optimized file is being delivered). You can also run a page-speed tool before and after. Just be sure to test after the cache has warmed.