Why in the browser
The usual way to compress or convert an image online is to upload it to a server, wait, and download the result. That works, and it means handing your file to a company whose retention policy you have not read, for a job your own device can finish in about a second.
Browsers have been able to decode, redraw and re-encode images natively for over a decade. Everything here uses that. Your file goes from your disk into the page and back out again, and never crosses the network.
What that changes
- Nothing is stored. There is no upload, so there is no copy on a disk somewhere with a deletion schedule you have to trust.
- It works offline. Once the page has loaded, the tools keep working with the network disconnected. That is a useful way to prove the claim to yourself.
- Large files stay fast. No waiting for an upload and a download on a slow connection — the only limit is your own device.
- There are real limits. A browser cannot encode every format, and a low-memory phone will refuse enormous images. Where a tool cannot do something, it says so rather than failing quietly.
How these are built
The decision logic behind the tools — how a target file size is reached, what is lost in a given conversion — is covered by an automated test suite that runs on every change. The encoding itself is checked in a real browser against generated images, asserting that output never exceeds a requested size limit. Where a tool has a hard guarantee, that guarantee is tested rather than assumed.
Credits
HEIC files — the format an iPhone saves by default — cannot be read by any browser except Safari. Converting them uses libheif, compiled to WebAssembly and served from this site, under the GNU Lesser General Public License. The licence text ships alongside it. It downloads to your browser only when you actually open a HEIC file, and your photo is decoded on your own device — the decoder comes to you, not the other way round.
How this is paid for
Display advertising on the pages. The tools are free, there is no account to create, and there is no paid tier holding back a feature. Ads see the page you are on; they have no access to the images you open in the tools, because those images never leave your device.
Contact
Corrections, bug reports and requests for a tool that does not exist yet are welcome via the contact page. Bug reports that include the browser you used and the kind of file involved get fixed fastest.