OnlyJPG – Client-Side PNG/HEIC/AVIF/PDF/etc to JPG
TL;DR: private, in-browser converter that turns pretty much any image file format into standard JPEGs. Everything runs locally. No uploads. This started as a five-minute job and forty hours later... I wanted to convert a HEIC without uploading it anywhere, so I wrestled Emscripten/WebAssembly to run Google's Jpegli inside a Web Worker. Now there's a small UI and it handles a bunch of formats. Just about the only thing it can't decode is JXL - but there's still some JPEG XL magic in there: XYB perceptual color quantization is enabled by default via Jpegli. The upside of all this…
In plain words
OnlyJPG is a browser-based image converter that transforms PNG, HEIC, AVIF, PDF, and other formats into standard JPEGs entirely on the user's device. All processing happens locally with no file uploads to servers, preserving privacy. The tool handles multiple image formats using Google's Jpegli engine compiled to WebAssembly, with perceptual color quantization enabled by default. It produces compatible JPEGs that work universally across platforms and devices.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
TL;DR: private, in-browser converter that turns pretty much any image file format into standard JPEGs. Everything runs locally. No uploads. This started as a five-minute job and forty hours later... I wanted to convert a HEIC without uploading it anywhere, so I wrestled Emscripten/WebAssembly to run Google's Jpegli inside a Web Worker. Now there's a small UI and it handles a bunch of formats. Just about the only thing it can't decode is JXL - but there's still some JPEG XL magic in there: XYB perceptual color quantization is enabled by default via Jpegli. The upside of all this over-engineering is privacy and compatibility: images are processed entirely on your machine and never touch a server; the output is a regular JPEG that works everywhere. I could have used a CLI, sure — but where's the fun in that? Would love feedback on edge cases and defaults. Tested on Firefox, Chrome, and Safari. Cheers!
Does the same job
all alternatives →- JJJXL.js – JPEG XL Decoder in JavaScript Using WebAssembly in Web Worker2022 · github.com · ▲112
Free JPEG XL Converter Jun 2026 · jpegxlconvert.com · ▲3Convert JXL, HEIC & more — free, private, in your browser
- PTPNG to PDF Conversion in the Browser2022 · png.to-pdf.net · ▲77
Hi everyone, I build some "online" converters as a side project in the last weeks. The difference to existing conversion websites is, that my converters don't upload your files. Everything happens in your browser on your device (with the help of a lot of great Open Source Javascript libraries). I think privacy is an essential feature for a service like this, so my converters also don't use google analytics or any other form of tracking (in fact they use no external resources at all). I started this because I ended up with some .heic files from my iPhone and had to use ImageMagick every time…
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