Compress images without uploading — how local browser processing works

Two different processing modes on ConverterFleet

Not every tool on ConverterFleet works the same way. Some operations — like server-side PDF optimization — briefly transfer the file to our server, process it there, and delete it afterward. Other operations, like image compression, run entirely in your browser: the file is never uploaded anywhere. Which processing mode a tool uses is shown as a clearly visible label on every tool page.

How local processing works technically

In the compress-images tool, your browser reads the selected file directly from your device and re-encodes it using the browser's own capabilities, at the quality level you choose. The resulting, smaller image is then offered for download. At no point in this process does the image file leave the device it was opened on. This is technically verifiable: checking your browser's network analysis while using this tool shows no file-upload request.

What this means for you

How much smaller an image gets depends heavily on the source image — there's no fixed percentage, photos with a lot of detail usually shrink more than already-optimized graphics. JPEG, PNG, and WebP files are supported (no HEIC — more on that in our HEIC article). For PNG images the quality setting has little effect, since PNG compresses losslessly by design.