How to check that a tool does not upload your files
Two simple checks, the browser’s Network tab and offline mode, to see whether a PDF or image tool works on your device or sends the file to a server.
Updated: 5 November 2026
Many free PDF and image tools say your files are “private” or “secure”, but those words can mean very different things. Some tools process the file on your own device. Others send it to a server, process it there and promise to delete it later. For a contract, an ID scan or a medical letter, it is worth knowing which kind you are using.
What the promises really mean
A padlock in the address bar means the connection is encrypted. It does not mean the file stays on your device, because an encrypted upload is still an upload. A statement such as “files are deleted after one hour” is a sign that files are sent to a server. A tool that works locally has no files to delete.
Check 1: watch the Network tab
- Open the tool page. In a desktop browser press F12 (or Ctrl+Shift+I, or Cmd+Option+I on a Mac) and open the Network tab.
- Clear the list, then run the tool with a test file.
- Look at the requests that appear. An upload usually shows up as a POST or PUT request about as large as your file. If nothing of that size leaves the page, the file was not sent.
Check 2: use it offline
Load the page, then turn off Wi-Fi or switch on airplane mode and use the tool again. If it still works, the processing happens on your device. Run the tool once while you are still online first, because some tools download a decoder or model the first time you use them. For example, the HEIC to JPG Converter fetches its decoder once and then works offline.
Signs that a file is being uploaded
- A progress bar labelled “uploading”, or a wait while “our servers” process the file.
- A promise to delete your files after a set time.
- Small file size limits, an account requirement or a limit on files per day, which are common with server-based services.
What these checks cannot prove
The Network tab shows what leaves your device while you are watching. It cannot show what a page might do later, and a page can use analytics that do not include your file. If a document is truly sensitive, the safest option is software installed on your own computer with the network disconnected.
Try it on these tools
On QMO Tools Pro you can run both checks on any tool. The Compress PDF, Image Compressor and Merge PDF read and change your files with JavaScript running in your own browser.