Check for yourself that a tool does not send your files
Published · Updated 3 min read
An online tool can process your file in your browser, or send it to a server. The look of the page does not let you tell them apart, and the promise written on the site is not always enough, especially for a sensitive document. The browser, however, keeps a trace of everything that goes out: you only need to know how to read it. Two checks take a few minutes and work for any service.
First method, the Network tab
- Open the tool, then the browser's developer tools with the F12 key.
- Choose the Network tab and clear the list.
- Add your file and start the processing.
- Look at the Method column (in Chrome and Edge, add it with a right-click on the column header): a file sent to a server appears in a POST or PUT request, whose body has the size of the file.
What Lmaotools tools show
For eight Lmaotools tools, the result appears without any request carrying the file away.
| Tool | File processed | Requests during processing | POST or PUT sends |
|---|---|---|---|
| Compress PDF | 7,9 MB | 3 | 0 |
| Protect PDF | 226 KB | 5 | 0 |
| Compress image | 1,9 MB | 2 | 0 |
| Image metadata | 68 KB | 1 | 0 |
| File hash | 669 KB | 0 | 0 |
| Convert audio | 669 KB | 6 | 0 |
| Remove the background of an image | 1,0 MB | 18 | 0 |
| Compress video | 14,7 MB | 4 | 0 |
All these requests go to the site itself. The transcription tool, which is not in this table, also downloads its model from outside.
The requests that appear anyway
Some tools load their engine at the time of first use: the audio converter and the video compressor download three files (a script, an engine and a calculation module), and background removal loads a model split into several parts. These requests are GET downloads: files come down to your browser, nothing goes up. The case of audio to text is a little different: its model is downloaded from services outside the site, after a consent box, and the detail is given in Turn a recording into text.
Second method, cutting the connection
Load the tool's page, then cut the connection, with the offline mode of the Network tab or airplane mode. Add your file. Offline, four tools produce their result: the hash of a file, the metadata of an image, the compression of a PDF and that of an image.
A tool that loads an engine on first use needs the connection for that loading, before processing. Its failure offline does not indicate a sending: try again after loading.
What the method does not prove
It shows what goes out during the check. A page may also contain other requests, for example audience measurement or fonts. Look at the body of the requests and their size, not only their number: a file of several MB being sent does not go unnoticed. Browser extensions can also add their own requests.
The same method for any service
These two checks apply to any online tool. Do them with an unimportant file before entrusting a sensitive document to a service.
Summary of the check
- Open the Network tab and clear the list.
- Process a file and look for POST or PUT requests.
- Cut the connection after loading and start again.
The tools cited here are described in Choose the compression level of a PDF and Check that a file has not changed using its hash.
When to do it
Before entrusting a contract, an ID document, a payslip or a medical file to an online service: two checks take a few minutes and work for any tool.
Frequently asked questions
- How do you know whether a site sends my file?
- Open the Network tab with F12, process a file and look for a POST or PUT request whose body has the size of the file.
- What do the GET requests that appear mean?
- They are downloads: an engine or a model comes down to your browser, nothing goes up.
- Is a tool that works offline safe?
- It is a good sign: it does not need the server to process your file. A tool that loads an engine on first use needs the connection for that loading.
- Do these checks prove everything?
- No. They show what goes out during the check. A page may contain other requests, for example audience measurement.