Why heicly
- Photos never leave your device
Conversion runs in your browser; your photos are not uploaded to any server.
- No upload wait
Your photos are converted on your device, with no upload step; speed depends on your device and photo size.
- Works offline after first use
After one conversion online, the page and engine stay cached so you can keep converting without a connection (as long as your browser keeps its cache).
How to convert HEIC to JPG offline
- Open this page while online. The first time, the page loads from the web like any other site. No photo is involved yet.
- Convert one photo. Choose any HEIC file. This downloads the conversion engine and lets your browser keep it, together with this page, for later use.
- Go offline and keep converting. Disconnect from the internet, reload this page if you like, and convert more photos. Each JPG is saved to your device as a normal download.
How HEIC to JPG conversion works without uploading
When you choose a file, the page reads it from your disk into the browser's memory. A Web Worker, a background thread of this page, decodes the HEIC image with a WebAssembly build of the open-source libheif library, corrects the orientation, and encodes a JPG. The finished JPG goes back to the page as a download link. None of these steps needs a server, which is why the conversion keeps working with the network switched off.
| Step | Where it happens |
|---|---|
| Reading the HEIC file | In your browser, from your disk or photo library |
| Decoding the image | In a Web Worker in your browser, using WebAssembly |
| Creating the JPG | In the same Web Worker |
| Packing a batch into a ZIP | In your browser's memory |
| Saving the result | Your browser's normal download, to a folder on your device |
Check it yourself: convert with the internet off
- Convert one photo while online and wait until the JPG is ready.
- Turn off Wi-Fi or unplug the network cable. On a phone, turn on airplane mode.
- Reload this page. It opens from your browser's cache.
- Choose a different photo. It converts even though there is no connection.
If the page does not open offline, the cache was not ready yet or the browser removed it, for example after you closed a private window or when storage was low. Go back online, convert one photo, and try again.
Check it yourself: watch the Network panel
Browser developer tools list every request a page makes. In Chrome, press Control+Shift+J (Windows) or Command+Option+J (Mac) and click the Network tab; other browsers have a similar panel. The panel only records while it is open, so open it before you choose a file (see the Chrome DevTools documentation).
| Request | What it is |
|---|---|
| A file named heic-to-worker-….js | The conversion engine, about 3 MB. It is downloaded on your first conversion; after that the browser reads it from its cache. |
| Entries starting with blob: | Data held in your browser's memory, such as the converter's background worker and the JPG you download. A blob: address points inside the browser; it is not a request to a server. |
| Analytics requests (Google Analytics, Microsoft Clarity, Cloudflare) | Usage measurement on the live site. They do not contain your photos, file names, or image data. |
| A request about as large as your photo | Does not appear. An upload would show up as a request whose size is close to the size of the file. |
Read the privacy notice for what the analytics services collect.
What offline use can and cannot do
- Offline use starts after one successful conversion while online. A first visit without a connection cannot load the page.
- Converter pages are stored separately. A converter page you have never opened while online may not be available offline.
- Browsers can delete stored site data when storage runs low or when you clear browsing data.
- Refreshing or closing the page clears the current tasks and results, so download the JPGs you need first.
- The output is the same online and offline: the same quality setting, and the same resizing of images above 16,777,216 pixels.
Offline conversion questions
Do I need to install an app to convert HEIC offline?
No. Your browser keeps this page and the conversion engine in its cache, so there is nothing to install. To remove them, clear this site's data in your browser settings.
Why does the first conversion need an internet connection?
The conversion engine is downloaded only when it is first needed, so the page itself opens quickly. Once it has been used, the browser keeps a copy and later conversions read it from the cache.
Is converting offline more private than converting online?
The photo stays in your browser either way; it is not uploaded online or offline. Switching the connection off is simply an easy way to see this for yourself.
Does offline conversion work on a phone?
It depends on the browser. The steps are the same: convert one photo online, then go offline. Mobile browsers may clear stored data more readily when storage is low, so try it once before you rely on it.
Is the JPG different when converted offline?
No. The same engine and settings run online and offline. A single photo starts at quality 90 out of 100 and can be adjusted; photos in a batch use quality 90.