A tool that runs on your own device does the work inside your browser, and a tool that uploads sends a copy of your file to a company’s computers first. You can tell which kind you are using with a test using the wifi, by reading what the page says it does with your file, and, if you wish, by watching what your browser sends.
Last reviewed 3 October 2026. The steps work the same on any phone or computer, and with any website.
Two kinds of online tool
An upload tool asks you to choose a file, sends it over the internet to the company’s computers, does the work there, and sends the result back. A copy of your file exists on those computers, and the company’s own rules decide how long it stays.
An on-device tool loads its program into your browser and then does the work on your own phone or computer. Your file stays where it was.
Many upload tools are run carefully. The difference is who you rely on: with an upload tool you rely on the company’s rules and security as well as your own, and with an on-device tool the file never leaves your hands.
Three ways to tell
1. Switch the wifi off
Open the tool’s page and wait until it has fully loaded. Then switch off the wifi and mobile data, or turn on aeroplane mode, and use the tool. If it still works, the work is happening on your device. If it reports an error or asks you to reconnect, it needs the internet to do its job. This is a good sign and not a proof, because a page could in principle work offline and send the file later.
2. Read what the page says
Look for plain statements about your file. Words such as “upload”, “we process your file”, “deleted after one hour”, “sign in to download” or “we will email you the result” describe an upload tool. An on-device tool says the file stays on your device, and its privacy page should say the same.
3. Watch what your browser sends (optional)
On a computer, press F12 (or Ctrl+Shift+I on Windows, Cmd+Option+I on a Mac) to open the browser’s developer tools, a panel built into the browser. Open the tab called Network, then choose a file in the tool. If a line appears for a request carrying your file to another address, the file was uploaded. If no new line appears, nothing was sent.
What “secure upload” means
A padlock or the word “secure” means the file is scrambled while it travels, so people on the way cannot read it. The company at the other end receives it in readable form. It does not tell you how long the company keeps the file or who inside it can open it.
What UtilForge does
Every UtilForge tool page tells the browser not to allow the page to make network connections for data, which blocks the usual ways a page sends information to another website. The tool pages say they work with the wifi off, and you can repeat the three checks above on any of them. Is It Really Blacked Out? and Release Check are good ones to try with a document you care about.
When an upload tool is the better choice
Some jobs need a company’s computers, such as reading text from a very large scan or working on a file with other people at the same time. If you use an upload tool, pick one that states how long it keeps files, that deletes them when it says it will, and that does not ask for an account. A useful rule is to upload only what you would be comfortable posting to a stranger.
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Then turn the wifi off.
Is It Really Blacked Out? runs on your own phone or computer. What you choose stays on your device.