Finding conflicts
The conflict report — what each kind of problem means, which ones are advisory, and what dismissing one actually does.
Because the app lets you create clashes on purpose, it also has to be good at showing you the ones you have. The Conflicts button opens the full report; individual pills carry a badge when they are involved in one.
The number on the Conflicts button counts only clashes: room, teacher and student group conflicts. Other problems, such as a missing room, do not make the button red. If there is no clash but there are other problems, the button says No Conflicts and shows their number in grey. The report itself lists every kind.
The report opens on a summary, then breaks the problems down by whether they are about rooms, teachers or student groups. When there is nothing to report it says so plainly rather than showing you an empty list.
Rooms
Missing rooms — the lesson has no room at all. Not strictly a clash, but it is unfinished, and a lesson with nowhere to happen will not survive contact with a real school day.
Room conflicts — two lessons in the same room at the same time. The unambiguous kind.
Rooms outside the preferred list — the lesson is somewhere it was not supposed to be. You may have decided that deliberately; the report is telling you it happened, not that it is wrong.
Rooms too small — the room's capacity is below the class size. Only as reliable as the capacities recorded against your rooms, which is a good reason to fill them in.
Rooms that may overlap — a virtual room may need a real room that is already in use. This one is marked advisory in the report itself (so are rooms too small), and the wording is deliberate: a virtual room stands for a set of real ones, so whether this is genuinely a clash depends on which real room ends up being used. Treating it as certain would be overstating what is known.
Teachers and student groups
Missing teachers and missing groups — the lesson has not been fully defined yet.
Teacher conflicts — the same teacher in two places at once.
Group conflicts — the same students expected in two places at once. Worth checking carefully when your groups share students, since a subgroup clash is easy to create and hard to see by eye.
Dismissing
Every problem can be dismissed, individually or a whole category at a time, and there is a control to dismiss everything at once.
Dismissing is the right response to a conflict you have looked at and accepted — two lessons that share a room because they genuinely share a room, a capacity warning on a class that is never all present. It keeps the report meaningful: a list of twelve problems you have decided about is worse than a list of two you have not.
Two things to know about dismissals. They are remembered in the browser you are using, so a colleague opening the same timetable still sees every problem, and your own dismissals do not follow you to another machine. And they hide the report entry, the badge on the lesson and the count on the Conflicts button, not the underlying clash — the timetable still has it, and so does the exported file.
There is no control to bring dismissed items back. Clearing this browser's site data for the timetable site removes all of your dismissals.
Badges on the grid
A pill involved in a conflict carries a badge, so the report is not the only place problems show up. If you want them to be harder to miss, the Lens can make those badges blink.
This is not the pre-flight check
The two answer different questions and it is worth keeping them apart.
This report describes clashes in the timetable you have built — who is double-booked, right now, on this grid.
The pre-flight check examines the rules for contradictions that make the timetable impossible to solve at all, before you export. A timetable can be free of conflicts here and still be refused by the pre-flight check, and the reverse is also true.
Run both.