Does this replace FET?

No. FET builds the timetable. This reads your file, proves what cannot work, shows it to people, and hands it back to FET unchanged.

No, and it is not trying to. FET generates timetables. Nothing here does that, and nothing here is planned to.

What FET does

FET takes your rules and searches for an arrangement that satisfies them. That search is the hard part of timetabling, it is very good, and it is free.

What this does

Four things FET does not set out to do.

It reads your file and tells you what cannot work. Before you start a search, the check does arithmetic on your rules. Where it can prove no arrangement exists, it says so in seconds and names the rules responsible. FET would find the same thing by searching, eventually, and without telling you which rules were to blame.

It edits the data comfortably. Activities, teachers, rooms, student groups and every constraint, in a browser, on a screen bigger than a dialog.

It shows the timetable to other people. Teachers, classes, a screen in the corridor, a page on your school website — without giving anyone your file.

It keeps the file safe. Versions, backups, and a download whenever you want it.

Your file stays yours

What you import, you can download again as a .fet file. It opens in FET.

The version stays the version your file declared. We do not upgrade it and we do not stamp our own.

⛔ Rules we do not recognise are written back unchanged. If your file uses something this product has never heard of, it survives the round trip in place rather than being dropped. That is a deliberate promise, because a tool that quietly loses part of your work is worse than no tool.

So the order of work is

Build your rules — here or in FET, whichever you prefer.
Run the check, and clear anything it proves impossible.
Download the .fet file and let FET do the search.
Bring the result back to show people, print it, and share it.

The honest limit

A clean check is not a promise that FET will solve your timetable, or solve it quickly. The check proves impossibility; it cannot prove possibility. See What it cannot tell you.