What leaves your computer
Your .fet file stays in your browser. What travels, when it travels, and where it goes — each case separately, because they are not the same.
This question deserves a separate answer for each part of the product, because the answers really are different. A single sentence covering all of them would be either wrong or too vague to trust.
Your .fet file never leaves your browser
This is true everywhere. No part of this product uploads the file you chose.
Your browser reads it and works from what it read. The file stays on your disk.
The check at fetviewer.com/check
Your browser reads the file. It then sends a summary to our server, and the server does the arithmetic.
Every name in that summary is replaced by a number before it is sent. Your teachers, rooms, subjects and classes travel as 1, 2, 3. Your browser keeps the list that turns them back into names, and it puts the names back when it draws the report. The server never receives them and the request refuses to carry them.
The request carries no cookies. Nothing about the check is stored: not the summary, not the report, not your question.
⚠ The file itself may be up to 25 MB, and none of it is sent. The summary has its own, separate limit, and a file the summary cannot fit is refused rather than trimmed.
The pre-flight check inside your timetable
This check does not run in your browser either. Your browser sends a summary to our server, the same way the public checker does. Our server does the arithmetic and sends the findings back.
The summary carries no names. Teachers, rooms, subjects and student groups travel as numbers. Your browser puts the names back before it shows you the report.
We already hold that timetable, because you imported it. So the summary tells us nothing we do not already have.
We store nothing from this check: not the summary and not the report.
The assistant
Here it depends on the choice you made, and the page tells you which one is in force before you ask, while it works, and under the answer.
A model in your browser. Your question and your timetable stay in the tab.
A model on your own computer. Your question and your timetable stay on your computer. ⚠ If the model runs on another computer in your school, your question travels across your own network to reach it.
Your own provider key. Your question and the timetable summary go to the company whose key you pasted — Google, DeepSeek or whichever you chose. They are not sent to us. ⛔ This summary carries real names, because a model cannot answer a question about "teacher 7". You are asked to agree before this choice is used, and the agreement lists what goes.
Included with your plan. Your question and the summary come to our server. We pass them to the model we pay for. ⛔ This summary carries real names too, for the same reason. We ask you to agree before we use this choice, and the agreement lists what goes.
If you are signed in: our activity log records the step, the screen and the model you chose, never your question or the answer. With your own key or our key, we also count the words that the assistant could not match. That count has no link to you.
What is never sent, in any choice
The .fet file. The assistant works from the same summary you can read about above, not from the file.