TL,DR: A tool does not have to be an executable.
It could even be hardware, for example a hammer is a tool. If you invent a new hammer design and you want to submit it to the jam it is totally possible. Just keep in mind that people won’t be able to try it and it will be hard for people to rank your entry (but who cares being rated?)
In the same way if you make a tool that is only useful for godot users or c++ developers, it will only be usable by a few person. But it doesn’t matter as long as it’s useful for you and some other people.
so what is a tool for me?
Can a browser extension or a plugin be a tool ? Yes.
Can a python script be a tool ? Yes.
Is an open source game or demo (that you can modify to make your own game) a tool? I don’t think so.
Is super mario maker a tool? I don’t think so.
Is a diamond pickaxe in minecraft a tool? I don’t think so.
But that’s my personal opinion. If someone is really convinced of the contrary I won’t remove his entry.