After Converting PNG to WebP: A Compatibility Checklist for Safari and Older Browsers

After converting your images to WebP format, you may notice improved load times and visual performance in modern browsers like Chrome. However, older browsers such as Safari can experience compatibility issues when encountering WebP images. This compatibility checklist will guide you through verifying that your real visitors see the images correctly and provide a safety net while you transition away from PNG files.

First, incorporate the HTML picture element as your primary backup plan. The picture element allows browsers to select the first format they support, falling back to PNG if WebP is not understood. If you have been serving WebP images through URL rewriting instead, ensure your server also offers a fallback path for older user agents. Do not remove your original PNG files until you have completed this checklist.

Next, test your conversions on real Safari versions rather than just the latest one. Safari 14 and 15 support WebP, but the in-app browsers within messaging and social apps often lag behind the system version. Additionally, if your site relies on third-party embeds or widgets, these may hotlink your images and require a fallback. Browser testing services can help you create old Safari versions in the cloud if you lack access to such devices.

Inspect the images loaded by older browsers, checking for three key elements: the fallback PNG appearing when WebP fails, the preservation of transparency in transparent images, and CSS background images retaining their fallback. CSS lacks a picture element, so you'll need a separate rule for serving PNGs first and then overriding them with WebP for supporting browsers.

Remember to audit all places where images are used, such as hero images, Open Graph tags, email templates, favicons, and third-party embeds. Some platforms still prefer PNG or JPG, so maintaining a fallback version is crucial for these cases. After launch, monitor analytics for a week to catch any silent failures, such as image error rates segmented by browser version, layout shifts caused by failed images, or user complaints about missing images.

Only after all items on this checklist are green should you archive the original PNG files. Keep them in a safe location rather than deleting them entirely in case you need them for future projects, print assets, or platforms requiring PNG format. The benefits of WebP outweigh the initial conversion effort, as most visitors will remain unaware of the format change while enjoying faster load times and better image quality.