Why this one works in every browser
Reading an image format and writing it are two separate features, and browsers ship them separately. Every current browser can read a WebP, because that is what makes the format useful on the web at all. Writing one is rarer: Chrome and Edge can, Safari cannot.
WebP to JPG only needs the half that is universal. The WebP is decoded by the browser's own reader, and the pixels are written back out as JPG, which every browser has been able to write for twenty years. So this page behaves the same on Chrome, Edge, Firefox and Safari, on a desktop or a phone. The conversion that gets awkward is the other direction, and that is covered on the image converter page.
Where WebP files come from
Almost always from saving a picture off a web page. Sites serve WebP because it is smaller, and since about 2020 they have been able to serve it to nearly everyone. So you right-click, choose Save image as, and get a file your own computer then declines to open. Nothing has gone wrong. The site made a sensible choice for its bandwidth and you inherited the file.
The same thing arrives through screenshots on some Android builds, through images pulled out of a CMS, and through design handoffs where the exporter defaulted to WebP. If you are being asked for a JPG by a print shop, a marketplace listing or an old bit of company software, this page is the shortest route between the two.
What the conversion actually does to the picture
It decodes and re-encodes, which has one consequence worth stating plainly. WebP is a lossy format, and so is JPG, so the picture goes through a second round of throwing detail away. The first round already happened before you ever saw the file. This one is small at quality 85 and invisible on most photographs, but it is not nothing, and it is not reversible.
If you have any route to the original, use it. Converting from the source beats converting from a copy that has already been squeezed once. Where the WebP is all you have, which is the normal case, quality 85 to 92 is the range where the second pass costs you very little and the file stays a sensible size.
Two other things change. Transparency is lost, because JPG has no alpha channel: a WebP with see-through areas comes out with white behind them, chosen deliberately since browsers left to themselves fill that space with black. And metadata is dropped, so any EXIF, colour profile or GPS tag attached to the WebP is not carried across. For a picture going onto the public web, losing the location tag is the point.
If you need the transparency kept
Convert to PNG instead. PNG holds an alpha channel, loses nothing on the way through, and every piece of software that refuses WebP will happily open a PNG. The WebP to PNG page is the same tool with that format already selected. The trade is size: a photograph saved as PNG can be several times larger than the WebP, because PNG throws nothing away at all.