Does this website upload my files? How to check
A five-minute check with tools already in your browser. No trust required.
The claim and the check
Plenty of file tools now say "your files never leave your browser". Some mean it. The good news is that you do not need to trust any of them, including this site: every browser has a panel that lists each request a page makes, and an uploaded file is a request. Here is how to read it.
Step 1: open the network panel
Open the tool's page. Press F12 on Windows or Linux, Cmd-Option-I on a Mac, or right-click the page and choose Inspect. A panel opens; pick the tab labelled Network. Reload the page so the list starts fresh. You will see the page's own files load: HTML, scripts, styles, maybe a font, maybe a large file for a decoder. That is the site delivering its program to you, and it is expected.
Step 2: clear the list, then add a file
Click the clear button (a circle with a line through it) so the list is empty. Now drop your file onto the tool and run it. Watch the list.
Step 3: read what appears
Three outcomes cover almost every tool:
- An upload. A row appears with method POST or PUT, often to a path like /upload or /api/convert, and its size (the Size column, or the request's Payload tab) matches your file. The file left your computer. Everything the site says about deletion applies from here.
- Nothing, or only small pings. The list stays empty, or shows a few requests of under a couple of kilobytes to an analytics host. Your file did not leave. A row can also appear for a decoder or library the tool fetches on demand; that is a GET with no payload, and you can confirm it by clicking it: the request has no body.
- Chunks. Some uploaders split large files into many POST requests of a few megabytes each. The pattern is the same: outgoing requests with bodies that add up to your file.
Step 4: the airplane-mode test
For a second opinion that needs no panel at all: load the tool, switch on airplane mode or unplug the network, and run it. A tool that processes locally keeps working. A tool that uploads fails at once. This also catches the case where a site processes locally but "phones home" with the result.
What Stayput looks like in the panel
On any Stayput tool you will see the page and its scripts load, on the HEIC and JPEG XL pages one larger GET for the decoder program, and one small anonymous page-count request. After you add files: nothing, apart from that same small count when a tool finishes, which names the tool and a size bucket and never a file name. Each tool page also runs this count for you and lists the requests under "Open the network tab. It stays empty." The site is open source, so the third check is reading the code.
Questions
What if the site uses a web worker or WebAssembly?
Both run inside your browser and show nothing in the network list except the one-time download of their code. They are how local processing is done, not a way to hide an upload.
Can a site upload my file in a way the panel does not show?
No. Every request from the page goes through the browser and appears in the panel, including ones from workers and service workers. What the panel cannot show is what a server does after an upload.
Does "encrypted" mean not uploaded?
No. Encryption protects the file in transit. If a POST with your file's size appears, the file was sent, encrypted or not.
Do I need to be technical to do this?
No. Open the panel, clear it, drop a file, and look for rows with a size close to your file. That is the whole check.