About JXL Convert
JXL Convert is an independent project built and maintained by one person. It converts JPEG XL images without uploading anything, because the tool I wanted didn't exist.
by Robert Castillo Β· Published
Why this site exists
In 2026 you can still end up with a .jxl file that nothing on your computer will open. JPEG XL is an excellent image format β smaller files, better quality, no licensing strings attached β but software support arrived slowly and unevenly. Safari shows JPEG XL natively, Chrome has taken years to get there, and most phones, email clients and photo apps still shrug at the extension.
The usual answer is to upload your photo to some website, wait, and hope it gets deleted afterwards. That never sat right with me. Family photos, screenshots of documents, work files β none of that should have to travel to a stranger's server just to change format. So I built the version I wanted to use: everything happens inside your own browser, and the file never leaves your device.
How it actually works
The converter runs libjxl β the official JPEG XL reference implementation β compiled to WebAssembly so it executes inside your browser tab. When you drop a file in, your browser does the decoding and encoding with your own processor. There is no upload step, no queue, and no server that could keep a copy, because there is no server involved in the conversion at all.
Getting there took real work. The off-the-shelf WebAssembly builds available at the time would crash on large photos β anything past roughly 12 to 16 megapixels, which is well within what a modern phone produces. I ended up compiling libjxl myself with the memory settings raised so that full-resolution camera images convert without falling over.
Nothing is uploaded
The conversion happens in your browser. Your images stay on your device from start to finish.
Official codec
Built on libjxl, the reference JPEG XL implementation, compiled to WebAssembly.
No limits or accounts
No sign-up, no file-count limit, no watermark and no paid tier.
Who is behind it
My name is Robert Castillo. I build web tools on my own β this site is a personal project, not a company product, and I run it in my own time. I also write about what I learn while building it: the libjxl WebAssembly work and some of the analytics findings are published under my name on dev.to.
If something is broken, if a format you need is missing, or if you spot a mistake in one of the guides, write to me at robert.cas.sch@gmail.com. I read everything, and corrections to the guides are genuinely welcome β several pages have been fixed because a reader took the time to point something out.
How the site pays for itself
The converter is free and I intend to keep it that way. The domain and hosting cost money, so the site carries advertising to cover them. Ads are clearly separated from the tool and never interfere with converting a file.
What the site does not do is sell or share your images: it cannot, because it never receives them. The advertising is the only commercial element here, and the privacy policy sets out exactly what the ad system and the site's analytics do collect.