How browser-based file tools work (and why nothing gets uploaded)
javascript
dev.to
TL;DR: When a tool says your files never leave your device, that is an architectural claim, not a marketing one. Here is the stack that makes it true, and what it costs. Most online file converters follow the same shape. Your browser uploads the file, a server runs something like ImageMagick or headless FFmpeg, and you get a download link. The work is real, and often fast. The catch is that your file left your machine, and it now sits in storage you do not control, under a retention policy you