Why you keep getting WebP files
WebP is Google’s image format, and it is now what most large sites serve because it is meaningfully smaller than JPEG or PNG at the same quality. Save an image from a web page and .webp is what lands in your Downloads folder.
macOS has read WebP since Big Sur, so Preview and Quick Look open it without complaint. The trouble starts when you hand the file to something older: a document template, an upload form, a print shop, or a colleague on an older Windows machine.
Option 1 — Preview
Double-click the file to open it in Preview, then File → Export. Set Format to PNG or JPEG and save. That is the entire process for a single image, with nothing to download and nothing uploaded. Hold Option while opening the Format menu to see the full list rather than the short one.
Option 2 — Finder Quick Actions
For several files, select them in Finder, right-click, and choose Quick Actions → Convert Image. Pick JPEG or PNG, choose a size, and macOS writes the converted copies alongside the originals. Faster than Preview for a batch, at the cost of a real quality setting.
Option 3 — batch conversion
When it is a folder rather than a handful, or you need a specific pixel size and quality, the built-in tools start to chafe. SnappyEdit converts the whole set in one pass with real quality control, resizing, and a preview of the encoded result before anything is written. It also reaches well beyond PNG and JPEG — TIFF, HEIC, AVIF, PDF, and more — and never overwrites your source files.
PNG or JPEG?
PNG is lossless and preserves transparency, which matters for logos, icons, screenshots, and anything with text or sharp edges. JPEG is smaller and better suited to photographs. If the WebP had a transparent background, PNG is the only one of the two that will keep it.
Going the other way
WebP is a genuinely good format when the destination supports it, and a WebP is typically far smaller than the equivalent PNG. SnappyEdit exports WebP as well as reading it, which helps when you are preparing images for your own site.
Converting photos from an iPhone instead? See converting HEIC to JPEG on a Mac.