Compress and convert images without uploading them

Short answer

You can compress, resize and convert images entirely in a browser tab, with the file never leaving your device. Tools like Squoosh decode the image, re-encode it with modern codecs such as WebP and AVIF, and hand you the result — all using your own processor. There is no upload, so there is no wait and no copy of your photo on someone's server. For single images and small batches it is faster than any desktop tool, because there is nothing to install.

Why nothing is uploaded

Image codecs have been compiled to WebAssembly, which means a browser can now run the same encoders that desktop tools use — at close to native speed, on your own machine. The file is read from local disk, decoded, re-encoded and offered back as a download.

That removes the round trip entirely. For a 12 MP photo the difference is not subtle: no upload, no queue, no download of the result — just the encoding time. And no server ever holds your image, which matters for anything you have not published yet.

Mentioned here: 🗜️ Squoosh, 🖼️ Photopea

Choosing a format without guessing

The useful feature of a good browser compressor is the side-by-side preview: original on the left, compressed on the right, with a slider. You can push the quality down until you see the damage, then back off one notch. That is a far better method than picking 80% and hoping.

AVIF gives the smallest files and is now widely supported; WebP is slightly larger with broader legacy support; JPEG remains the safe default for anything that must open everywhere. For screenshots and graphics with flat colour, PNG or lossless WebP will beat all of them.

When to reach for something else

Large batches. Browser tools handle images one at a time or in small groups; a folder of 500 photos wants a command-line tool or a proper batch application.

Editing rather than compressing. If you need layers, masks or retouching, that is a photo editor's job, not a compressor's.

Very large files. Decoding happens in browser memory, so a 100 MP panorama may exceed what a modest device can hold.

Frequently asked

Is the quality as good as desktop software?

Yes — these tools use the same encoders, compiled to WebAssembly. The output is byte-comparable to what a command-line encoder produces at the same settings.

Does it work offline?

Once installed and loaded once, yes. The codecs are cached with the app, so compression works with no connection.