What is a WebP file? Why your images save as WebP

What is a WebP file?

A WebP file is an image in Google’s WebP format, made to carry pictures over the web in fewer bytes. Google announced it on 30 September 2010 as a developer preview, built on VP8, the video codec it had open-sourced that May. Its launch test re-encoded about a million web images, mostly JPEGs, and they came out 39% smaller on average.

The file ends in .webp and servers label it image/webp. Inside, a WebP is a small RIFF container, the same wrapper a .wav sound uses, holding one of two kinds of picture. A lossy WebP is VP8 still-image coding; a lossless WebP uses a separate format Google built for the job, VP8L. The format became an RFC in November 2024, RFC 9649, an informational document rather than an internet standard.

Why do images save as WebP?

The website chose WebP for your browser, and Save image as kept what arrived. The name in the address does not decide the format. We proved it with one public image whose address ends in .jpg, Cloudinary’s demo photo with automatic format, fetched by the three browser engines and by two written requests on 2 October 2026:

One .jpg address, five different files

How the site picks the format

Each browser sends a list of the image formats it can show, the Accept header, with every request. Chromium’s, read from the request it made:

Google’s WebP FAQ tells servers to do exactly this: send WebP when the browser says it accepts image/webp. Cloudflare’s Polish keeps the same image addresses and serves the WebP version only when the Accept header from the browser includes WebP, and Shopify stores have served WebP automatically since July 2019. The order of the list does not decide: the service picks from the formats listed, by its own preference. At this address Chromium and Firefox got AVIF, WebKit got JPEG XL although it lists WebP first, and a browser that lists WebP alone got WebP.

How to stop images saving as WebP, or save as JPG instead

Chrome and Edge have no setting for it. Their image Accept header is fixed in the browser, and a Chromium request to let you download a JPG or PNG from a WebP has been open since May 2024. What works depends on the site, so here is what each option really does.

1. 1

   Convert the file you saved

   Always works. Decode the WebP and write a JPG or PNG with a converter, Photoshop 23.2 or later, GIMP, or Preview on a Mac (File > Export). A WebP that was lossy becomes a JPG through a second lossy step, so choose a high quality, or PNG.

2. 2

   In Firefox, stop asking for WebP

   Open about:config and set image.http.accept to image/png,image/*;q=0.8,*/*;q=0.5. Sites that choose by the Accept header then have no WebP to send you. The old image.webp.enabled switch no longer exists. The change also drops AVIF, and a site that stores only WebP still sends WebP.

3. 3

   Change the format in the address

   On some image services the format sits in the link. On Cloudinary, f_auto becomes f_jpg; on Cloudflare’s image transforms, format=auto becomes format=jpeg. Shopify treats a format in the link as a hint, so it may still send WebP.

How to open a WebP file on Windows, Mac, iPhone and Android

Any current browser opens one: drag the .webp into Chrome, Edge, Firefox or Safari. Browser support is close to universal, at 96.74% of browsers in use by caniuse’s count of 30 September 2026. The apps outside the browser are where a WebP gets refused.

On Windows, the WebP Image Extension in the Microsoft Store is what lets Photos, File Explorer thumbnails and Office read the format. On a Mac, macOS reads WebP but does not write it. On our Mac (macOS 26.5), Preview lists WebP among the files it opens and exports one to JPEG, PNG or PDF with File > Export.

How to convert a WebP to JPG, PNG or PDF

Convert it when an app refuses it, or when someone needs a JPG. A conversion decodes the WebP and writes a new file. Here is what our engine made of our reference photo saved as a 611.2 KB WebP. That WebP was saved at a high quality, which is why the JPG at Auto comes out smaller than it:

1. 1

   For a JPG any app opens

   Drop the files into the WebP to JPG converter. Auto picks a quality per photo; a JPG has no transparency, so see-through parts turn white.

2. 2

   For a logo or a screenshot

   Use WebP to PNG, which keeps transparency. Choose quality 100 when every pixel must match.

3. 3

   For a document

   WebP to PDF puts each image on its own A4 page, turned to fit it, in the order you drop them, up to 10 WebP files a run.

Is WebP better than JPG?

Usually smaller, by an amount that varies. Google’s own figure is that a lossy WebP is 25% to 34% smaller than a JPEG at the same quality, measured in 2011 against libjpeg 6b, and the explainers that rank for this question repeat it without a test of their own. We saved our camera photo at two sizes and our reference photo as JPG and as WebP, both at Auto, and the WebP was smaller on all three.

On the full 9.8 MB camera photo the WebP was 46% smaller than the JPG, and at 1920 pixels wide it was 39% smaller. On our 1920 × 1280 reference photo, one of our photographs, it was only 20% smaller. That spread shows that the 25% to 34% is an average, not a promise. Test your own pictures before you switch a whole site to WebP.

The same photo under one size limit

Size alone hides quality, so we also capped one photo at 70 KB in both formats and compared the result with the original. The WebP landed at 69.2 KB with a PSNR of 36.9 dB, the JPG at 69.6 KB with 35.9 dB. Higher PSNR means closer to the original, so at the same size the WebP kept more of the picture. The JPG shows its 8 × 8 blocks in the sky; the WebP smooths them.

WebP vs PNG: transparency and lossless files

WebP does both jobs people keep PNG for. It holds transparency, and it can store a picture losslessly, with every pixel kept. The difference is in the details. A soft-edged logo keeps its fade in a WebP: our engine’s WebP of a 512 × 512 logo kept 247 levels of transparency in 9.4 KB. The PNG at Auto saved 4.2 KB by keeping only 7 levels, so its edge steps. A JPG cannot be see-through at all.

Lossless WebP is usually smaller than a lossless PNG, by how much depends on the picture. On our three test subjects the saving ran from 18% on a photo to 54% on a card of text and 88% on a flat graphic. Google quotes 26% smaller than PNG; the study it links reports 23% against ZopfliPNG and 42% against libpng.

Can a WebP file be animated?

Yes. A WebP can hold many frames with a delay each, like a GIF, and it is far smaller. We built the same 12-frame clip of 480 × 270 pixels both ways: 116.0 KB as an animated WebP against 738.3 KB as a GIF, 84% smaller. The GIF also has to squeeze every frame into 256 colours, which shows as speckled dithering in a sunset.

Is a WebP file safe to open?

Yes, on an updated device. In September 2023 a flaw in libwebp, the library most apps use to read WebP, let a crafted image write past its memory, and Google said an exploit existed in the wild. Chrome fixed it on 11 September (version 116.0.5845.187), Firefox on 12 September (117.0.1) and libwebp itself on 13 September (1.3.2). The flaw was in the reader, not the format, and every image decoder carries the same kind of risk. Keep the browser, the system and your image apps updated.

When to keep a WebP, and when to convert it

Going the other way, a JPG or PNG for your own site is worth turning into WebP, or into AVIF, which is smaller again on most photos. Our post on what an AVIF file is covers that format, and compress WebP shrinks the WebP files you already have.