Privacy
Is it safe to put files into online tools? How no-upload tools work
What happens to your file when you use an online PDF or image tool, how tools that work without uploading differ, and how to check for yourself in two minutes.
Two kinds of online tool
Most online converters work like a post office. Your file is uploaded to the company’s server, processed there, and the result is sent back for you to download. For a while, a copy of your contract or passport scan sits on a computer you don’t control, under a privacy policy you probably didn’t read. Many services delete files after an hour or so, and many are trustworthy, but you can’t verify either.
The second kind does the work inside your browser. The web page arrives with the program code included; when you choose a file, JavaScript reads it from your disk into the tab’s memory, processes it there, and offers the result as a download. The file never travels over the network. deskumo’s tools, from Merge PDF to Compress Image, work this way.
How browser-based processing is possible
Modern browsers are powerful runtimes. They can read files you choose, decode and re-encode images on a canvas, run full PDF libraries such as pdf-lib and Mozilla’s PDF.js, and use the processor’s full speed. In our tests, merging 50 PDF pages took 0.06 seconds and rendering 10 PDF pages as images took 0.52 seconds on an ordinary 4-core computer.
There are limits. Very large jobs depend on your device’s memory, and some tasks, such as high-quality OCR or video conversion, need large downloads of code before they can run locally.
Check it yourself in two minutes
You don’t need to take any site’s word for it.
- The network test. In Chrome, Edge or Firefox, press F12 (or right-click → *Inspect*) and open the Network tab. Use the tool on a file. You will see the page’s own files, and on deskumo analytics and ad requests too, but no request whose size matches your file being sent out.
- The airplane-mode test. Open the tool page, then switch off Wi-Fi or turn on airplane mode. If the tool still processes your file, it can’t be uploading it.
Both tests work on any site that claims to process files locally.
What still goes over the network
Honesty matters here. Even a no-upload site makes some requests:
- The page itself, its scripts and stylesheets.
- Analytics, if the site uses it. On deskumo, Google Analytics records events such as “tool started” and the format of a download, never file names or contents.
- Advertising. Ads are loaded from Google’s servers and use cookies, as described in our privacy policy.
None of these requests carry your file. If you want to avoid analytics and ads as well, the airplane-mode test shows that the tools keep working without any connection once the page has loaded.
Good habits with any online tool
- For sensitive documents such as IDs, medical letters, payslips and contracts, prefer tools that process locally, and check with one of the tests above.
- Read what the service says it does with files, and how long it keeps them.
- Be wary of tools that ask you to sign in or install an extension just to convert a file.
- Keep your originals, and check the result before you send it.
The same applies to text: when you paste a draft contract into Text & Code Diff Checker or a private document into any text tool, it is worth knowing whether it leaves your device.