Are online tools safe? What happens to your files
Most people paste text or upload a PDF into a free online tool without thinking about where it goes. Usually it goes somewhere — to a server you don’t control, run by a company whose privacy policy you have not read.
That’s fine for a holiday photo. It is not fine for a bank statement, a signed contract, or an unpublished manuscript.
Two kinds of online tools
Server-side tools send your file over the internet to a machine that does the work and sends a result back. This is how most PDF converters and image compressors work, because the processing is genuinely heavy. The trade-off is that your file sat on someone else’s disk, at least briefly.
Client-side tools do the work inside your browser using JavaScript or WebAssembly. Your file never travels anywhere. The trade-off is that very heavy jobs can be slower on an old phone.
How to tell which one you’re using
There is a simple test that doesn’t require any technical knowledge: turn off your internet connection, then use the tool.
If it still works, the processing is happening on your device and nothing is being uploaded. If it fails or hangs, your file is going to a server.
You can also open your browser’s developer tools, switch to the Network tab, and watch whether a large upload request fires when you select a file.
What to look for before uploading anything sensitive
- Does the site say explicitly where processing happens? Vague phrases like “we take security seriously” are not an answer.
- Does it say how long files are retained? “Deleted after one hour” is a real commitment. Silence is not.
- Is there a signup wall? A tool that demands an account before converting a PDF wants your data more than it wants to help you.
The short version
For anything you would not email to a stranger, use a tool that runs in your browser. For everything else, either kind is fine — just know which one you picked.
Every tool on Cooltility runs entirely in your browser. Nothing you paste or open here is ever uploaded.