Convert JPG to WEBP
Re-encode a JPEG as WEBP, usually 25–35% smaller at a matched quality.
How it works
WEBP's lossy mode is built on VP8 intra-frame coding, and it beats JPEG mainly through better prediction. Where JPEG transforms each 8×8 block in isolation, VP8 predicts a block from its already-decoded neighbours and codes only the difference, then runs an adaptive in-loop deblocking filter over the result.
In practice that is a 25–35% smaller file at visually matched quality on photographic content, and the gap widens at low bitrates where JPEG's block boundaries become obvious and WEBP's filtered output stays smooth. Pixel dimensions are unchanged; this is purely a compression swap.
Re-encoding an already lossy JPEG
One caveat matters more than the saving. Your JPEG is already lossy, and decoding it and re-encoding it quantises the image a second time with a different transform. Worse, the second encoder cannot tell artifacts from detail: it spends bits faithfully reproducing the block edges and ringing that the JPEG introduced.
If you have the original (a camera raw, a PNG export, the master from the editor), convert that instead and skip a generation. If the JPEG is all you have, convert once at a quality near the source's own and do not iterate: repeatedly running an image through lossy encoders is how photographs acquire that soft, smeared look.
When the lossless toggle helps
The lossless toggle reproduces the decoded JPEG pixels exactly, artifacts included. On a photograph the result will be substantially larger than the JPEG you started with, frequently several times larger, because you are asking a lossless codec to store material a lossy codec had already thrown detail out of.
It is the wrong setting for photographs. It is the right one when the file is a JPEG by accident: a screenshot, a chart, a scanned document or a logo that someone saved in the wrong format. For those, WEBP lossless often lands smaller than the JPEG while removing no further detail.
Editors and upload forms
Every browser shipped since 2020 renders WEBP, including Safari from version 14, and Windows and macOS both preview it in the file manager. The friction that remains is elsewhere: some older desktop editors cannot open it, and a number of upload forms still reject the extension by name rather than by content type. Check the destination before converting a batch.
libjpeg-turbo in, libwebp out
Decoding uses a WebAssembly build of libjpeg-turbo, encoding uses libwebp, and both run in a Web Worker on your own hardware. There is no queue and no file cap beyond your device's memory.
Questions
How much smaller will the WEBP be?
For photographs, usually 25–35% smaller than a JPEG of comparable visual quality. The saving is larger for images that were only lightly compressed to begin with and smaller for a JPEG that was already squeezed hard — there is less left to remove. The result panel shows the actual byte delta for your file.
Is my image uploaded to a server?
No. Open developer tools, go to the Network tab, and convert a file. You will see the page's script and the two codec modules load, and nothing carrying your image. There is no upload request because the encoding happens in a Web Worker in this tab.
Should I turn on lossless?
Not for photographs; it will produce a much larger file than the JPEG. Use it when the source is a screenshot, diagram, chart or logo that happens to be stored as a JPEG, where lossless WEBP often beats the JPEG on size and stops the artifacts from getting any worse.
Will the WEBP look worse than the JPG?
At quality 78 and above the difference is generally not visible at normal viewing size, though a second lossy pass has still occurred and a pixel-level comparison will show it. If the image is going to be edited or re-compressed again afterwards, work from the original rather than from this output.