You right-click a product photo, choose Save Image As, and the file lands in your downloads folder as photo.webp. The page showed an ordinary picture. The URL may even have ended in .jpg. Then you try to drop it into a slide deck, attach it to a form, or open it in an older image viewer, and it is refused.
Nothing went wrong with the download. The website sent you a WebP, because WebP is smaller than the JPG or PNG it replaced and every current browser displays it. The friction appears only when the file leaves the browser. This guide explains what WebP is, why so many saved images arrive in that format, where it still fails, and how to convert it into something the next program accepts, or convert your own images into it.
TL;DR: WebP is an image format from Google, specified in RFC 9649, that supports lossy and lossless compression, transparency and animation in one file type. Websites serve it because it is smaller than JPG and PNG, so Save Image As often gives you a .webp even when the page URL says .jpg. Every current browser displays WebP, but some desktop apps, email clients and upload forms still reject it. Convert with WebP to PNG to keep transparency, WebP to JPG for the widest support, WebP to GIF for animation, or WebP to PDF for documents. All of them run client-side, nothing uploaded, free, no signup.
What is WebP?
WebP is a raster image format that Google released in 2010 to make images on web pages smaller. It is now documented by the IETF as RFC 9649, WebP Image Format, published in 2024. The RFC describes one container with two compression methods, plus optional transparency and animation, so a single format covers the jobs that JPEG, PNG and GIF split between them.
The file is a RIFF container, the same chunked structure used by WAV audio. Its first twelve bytes say so:
$ xxd -l 12 photo.webp
00000000: 5249 4646 3a1f 0100 5745 4250 RIFF:...WEBP
RIFF, four bytes of length, then WEBP. Inside are chunks: VP8 for lossy image data, VP8L for lossless, ALPH for a transparency channel, and ANIM and ANMF for animation. Tools that identify files by their bytes, including the Toolz converters, look for exactly that signature, which is why a WebP saved with a .jpg name is still recognized as WebP.
How does WebP compress images?
WebP has two separate compression methods, and which one a file uses changes what it is good for.
Lossy WebP is based on the keyframe coding of the VP8 video codec. The encoder splits the image into blocks, predicts each block from pixels it has already coded, and stores the difference with coarser or finer rounding depending on the quality setting. It also stores color at half the width and half the height of brightness, a technique called chroma subsampling. Eyes are less sensitive to color detail than to light and dark, so photographs hide this well. Thin colored lines and small red text on a flat background do not, and can pick up soft fringes.
Lossless WebP is a different algorithm entirely. It reproduces every pixel exactly, using predictive transforms, a color cache and LZ77-style back-references, and it competes with PNG rather than JPEG.
Either kind can carry an alpha channel for transparency. Lossy WebP with alpha is the combination PNG cannot offer: a photographic cutout with a soft transparent edge in a small file.
Google's published figures, on its WebP overview page, put lossless WebP at 26% smaller than PNG and lossy WebP at 25 to 34% smaller than comparable JPEG at equivalent SSIM quality. Those are averages over test sets. A given image can save more or less, and a JPEG that was already heavily compressed often saves little.
Why do saved images come out as .webp?
Saved images come out as .webp because the server chose to send WebP to your browser, and Save Image As keeps whatever bytes were delivered. There are three common ways that happens.
Content negotiation. Every image request your browser makes carries an Accept header listing the formats it can display. HTTP content negotiation, defined in RFC 9110, lets the server pick a representation based on that header. Image CDNs and many hosting platforms read it and return WebP or AVIF to browsers that accept them, while older clients receive JPEG from the same URL:
GET /images/product-42.jpg HTTP/1.1
Accept: image/avif,image/webp,image/apng,image/*,*/*;q=0.8
HTTP/1.1 200 OK
Content-Type: image/webp
The URL ends in .jpg. The response is WebP. When you save it, the browser names the file from the content type, so you get .webp.
The <picture> element. Sites that do not negotiate on the server can offer several formats in markup, and the browser picks the first one it supports, following the WHATWG HTML picture element rules:
<picture>
<source srcset="hero.avif" type="image/avif">
<source srcset="hero.webp" type="image/webp">
<img src="hero.jpg" alt="Product on a white background">
</picture>
Build pipelines. Site builders, WordPress optimization plugins and frameworks with image components convert uploads to WebP automatically. The site owner uploaded a JPG and never sees the WebP the visitor receives.
In all three cases the site is doing what performance audits recommend. The WebP is the smaller, correct file for display. It is just the wrong file for a program that was never taught to read it.
Which browsers and apps support WebP?
Every current browser displays WebP. Chrome and Edge have supported it for years, Firefox added it in version 65, and Safari added it in version 14, which brought iPhones and iPads along. On the web, compatibility is no longer a reason to avoid it.
Outside the browser, support is uneven. Some older image viewers, older office suites, email clients, print services and upload forms either do not open .webp or refuse it at the extension check. Operating system photo apps have mostly caught up, but a shared work computer or a piece of line-of-business software may not have.
Saving WebP is less universal than displaying it. The Toolz converters that write WebP use the browser's own encoder through a canvas. Current Chrome, Edge and Firefox can write WebP that way. Safari has long been able to display WebP but not always to save it, and when a browser cannot encode WebP, the converter shows an error saying so rather than handing back a PNG with a .webp name.
Why doesn't renaming a .webp to .jpg work?
Renaming a file changes its label, not its contents. A WebP renamed to holiday.jpg still begins with RIFF and WEBP, and still holds VP8 or VP8L data. Some programs look only at the extension, try to read the file as JPEG, find no FF D8 FF marker at the start, and report the file as damaged. Others sniff the bytes, notice it is WebP, and either open it anyway or refuse it with a clearer message.
Upload forms are the worst case. A form that checks only the extension accepts the renamed file, and then the server's image library chokes on it, or the image appears broken on the finished listing or profile page. A form that checks the bytes rejects it outright. Neither outcome is what you wanted, and both are harder to diagnose than the original refusal.
A real conversion is the only reliable fix, because it decodes the WebP into pixels and writes a new file whose bytes match its extension. It takes seconds and avoids a support ticket later.
How can you open a WebP without converting it?
Drag it into a browser window. Any current browser displays a local .webp file directly, which is the quickest way to look at one on a computer whose image viewer refuses it. From there you can view, zoom and print it.
Most current operating system photo apps also open WebP, so a double-click may work on an up-to-date machine even when a specific editor or office program on the same machine does not. When a program you depend on cannot read WebP, check for an update or a format plugin first; if neither exists, convert a copy and keep the original.
Opening is not the same as using, though. If the image has to go into a document, a form or an email, the recipient's software matters as much as yours, and a JPG or PNG removes that uncertainty.
WebP vs JPG vs PNG vs GIF: how do they compare?
WebP overlaps with all three older formats, which is both its appeal and the reason converting away from it needs a choice of target.
| Attribute | WebP | JPG | PNG | GIF |
|---|---|---|---|---|
| Specification | RFC 9649 | ITU-T T.81 | W3C PNG | GIF89a |
| Compression | Lossy or lossless | Lossy | Lossless | Lossless, 256 colors |
| Transparency | Full alpha | None | Full alpha | On or off per pixel |
| Animation | Yes | No | No (APNG aside) | Yes |
| Photo file size | Small | Medium | Large | Poor fit |
| Browser display | All current browsers | Universal | Universal | Universal |
| Desktop apps and forms | Patchy | Universal | Near universal | Universal |
| Best use | Serving images on websites | Sharing photos anywhere | Screenshots, graphics, editing | Simple animations everywhere |
The JPEG specification is ITU-T T.81 and PNG is defined by the W3C PNG specification. The practical reading of the table: keep WebP on the web, and convert when the file has to go somewhere the right-hand columns describe.
Which format should you convert a WebP to?
Choose the target by what the WebP contains and where it is going. Transparency, animation and destination decide it.
| Your WebP is | Going to | Convert to | Tool |
|---|---|---|---|
| A logo, icon or cutout with a transparent background | Anywhere | PNG | WebP to PNG |
| A photo | Email, forms, print, older software | JPG | WebP to JPG |
| An animation | Forums, chat, email signatures, wikis | GIF | WebP to GIF |
| One or more images | A document someone will print or file | WebP to PDF | |
| A mix of formats, or a target not listed | Various | Any | Image Converter |
For transparent images, choose PNG. The WebP to PNG converter keeps the alpha channel, so a logo on a transparent background stays transparent. PNG is lossless, so the output holds the decoded pixels exactly. It is usually larger than the WebP, because lossless storage costs bytes.
For photos that need to open everywhere, choose JPG. When you turn a WebP into a JPG, you get the format every upload form accepts. JPG has no transparency, so any transparent area is filled with white and a note under the result says it happened. The Quality slider runs from 10 to 100 and starts at 90.
For animations, choose GIF. An animated WebP saved from a reaction clip will not play in many forum editors or email signatures. The WebP to GIF converter writes every frame with its original delay and loop count. Reading the frames uses the browser's ImageDecoder API from the W3C WebCodecs specification, which Chrome and Edge support today. In Firefox and Safari only the first frame can be read, so the GIF is a still, and the note under the row says so. GIF has 256 colors per frame, so gradients may band, and soft transparent edges become hard ones. A frame with a delay under 20 ms is written at 100 ms, which matches how browsers play delays that short.
For documents, choose PDF. A WebP to PDF conversion puts one image on each page, in the order shown, in a single file. Since WebP is a lossy source, images are embedded as JPEG at 92% quality to keep the PDF small, or as PNG when an image has transparency. Pages can fit the image or use A4 or US Letter.
For everything else, use the Image Converter. It reads WebP along with JPG, JFIF, PNG, AVIF, GIF, BMP, ICO, HEIC, TIFF, PSD, SVG, CR2, DNG and PDF, and writes JPG, PNG, WebP, GIF, ICO, PDF or SVG, so a WebP can become a favicon or a traced SVG from the same page.
Should you convert your own images to WebP?
Yes, for images you publish on a website. Images are usually the heaviest part of a page, and a 25 to 34% saving on photos compounds across a catalog page with dozens of them. For images you email, print or archive, no: keep the original format.
Two converters handle the common sources. To convert JPG photos to WebP, start from the largest, least compressed original you have. A JPG is already lossy, so encoding it as WebP is a second pass, and the quality you start from is the ceiling. A setting of 80 to 85 is where most photos stop showing a visible difference on screen.
For graphics, screenshots and anything transparent, PNG to WebP keeps the alpha channel and usually cuts the file size sharply. Screenshots with small colored text need a higher quality setting than photos, because of the chroma subsampling described above.
Size limits in WebP itself rarely matter in practice. RFC 9649 caps a lossless WebP at 16384x16384 pixels, and lossy WebP is limited to a similar size by VP8, which is far beyond any image a web page needs. Very large panoramas or print-resolution scans are the only files that meet it, and those belong in a lossless master format anyway.
Keep the originals either way. The JPG or PNG is your master copy, and every future crop, resize or re-export should start from it rather than from the WebP.
How does client-side WebP conversion work?
Client-side conversion means the image is decoded and encoded inside the browser tab, and the file is never uploaded. WebP needs no extra download for this, because every current browser already contains a WebP decoder.
- The page reads the first bytes of each file and checks for the
RIFF....WEBPsignature. Each pair page accepts only its own source format, so a PNG dropped on the WebP to PNG page is pointed elsewhere. - The browser decodes the WebP into pixels.
- The pixels are drawn to a canvas and encoded as the target: PNG, JPG or WebP by the browser, GIF by a bundled encoder, or embedded into a PDF.
- You download each file, or the batch as a ZIP.
Drawing through a canvas has a side effect worth knowing: EXIF metadata, GPS coordinates and color profiles are not carried into the output. For an image about to be posted publicly, that is a privacy gain.
What are the limits and common errors?
Each limit produces a specific message on the file's row rather than a frozen tab.
Images over 100 megapixels are refused, because decoding them could exhaust the tab's memory. There is no separate byte-size cap for WebP, since the browser's own decoder handles it. Empty files are refused.
"This browser could not open the file" usually means the file is damaged or truncated, or is not a WebP at all despite its name. "This browser cannot save WebP files" appears only when converting to WebP in a browser without a WebP encoder; switch to current Chrome, Edge or Firefox.
When an animated WebP goes to PNG, JPG or PDF, only the first frame is kept, because those formats hold a single image. The WebP converters also write still WebP files only, so an animation converted to WebP keeps its first frame. Use GIF to keep the motion.
A daily conversion limit applies per tool. The tools are free, no signup, with no watermark.
WebP and the newer formats
WebP is no longer the newest option. AVIF, based on the AV1 video codec, often produces smaller files again and supports higher bit depths and HDR, and current browsers display it too. Sites that use the <picture> example above serve AVIF first and WebP as the fallback. The comparison of AVIF, WebP and JPG covers when each one is worth it.
If your problem is iPhone photos rather than web downloads, the format is HEIC, and the guide on HEIC vs JPG explains why those files fail to open. Every converter for both formats is listed on the image tools hub.
