Why “without uploading” matters
Most HEIC to JPG websites send the photo to a server, convert it, then send it back. That is fine for a meme. It is a bad idea for family photos, IDs, or anything with a house in the background. Location EXIF often travels with the file. A converter that never uploads cannot leak what it never receives.
How to check a site is actually local
Open Chrome or Edge DevTools (F12) → Network. Convert one photo. You should see the page’s JavaScript and maybe a WebAssembly decoder — not a POST or PUT of a multi-megabyte image. If a progress bar sits on “uploading…”, leave. Stayontab has no upload endpoint by design.
What still happens on your computer
The HEIC is decoded in this tab (Safari/Chrome native, or libheif in WebAssembly). Then the canvas writes a JPG. GPS and other EXIF are stripped. The original HEIC stays on disk unless you delete it. Convert a copy if you want to keep Apple’s file.
When a local converter is the wrong tool
Hundreds of 48 MP bursts on a cheap Android phone can run out of RAM. In that case, convert fewer files, or use a desktop app on the PC that already has the photos. Privacy does not require a website at all — it requires that the bytes never go to a stranger’s disk.
Ready? Use the HEIC to JPG converter — files never leave this device.