How to Check Whether Your Website Serves WebP Images
By George Nicolaou
Installing an image optimisation plugin does not prove that visitors receive WebP. The browser response is the place to check. My video shows how to investigate what your website actually serves.
Check the image request
- Open the page in your browser and open Developer Tools.
- Select the Network panel, filter for image requests, then reload the page. Disable the browser cache while testing if you need a fresh response.
- Select a photograph or other raster image request and inspect its response headers.
- Look for
Content-Type: image/webp. Compare the transferred size and preview with the original image.
A URL ending in .jpg can still return a WebP response when an optimiser negotiates the format. Equally, renaming a file to .webp does not convert its contents. SVG icons are a different format and do not need to become WebP.
If you still receive JPEG or PNG
Check that the optimiser has processed that image, that the page uses the optimised asset, and that its delivery rules are enabled. Clear the relevant page or CDN cache and test again. A picture element may offer several formats, so inspect the resource the browser selected rather than just the first URL in the page source.
Check the result beyond the format
Use dimensions appropriate to the display size and inspect the image for visible compression damage. A smaller file is useful only if the page still looks right. Repeat the check on more than one page because a hero image, gallery and background may follow different delivery paths.
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