You mentioned that it should be available on as many platforms as possible. 

So does that counts Browser extensions? Or Plugins? 

Framework to create specific mechanics? Like a platformer player script in godot or a demo project in unity that you can then use to build more of your game.

And about availability if the tool is a python script that you would need a text editor to run. Would  that count as a tool?

Or, anything other than a game counts as a tool? Such as if you can categorize it as a tool on itch.io then it's a tool. Which would include the demo projects to build your games around them however.

Because if it's a project file or code to build your game from, then it would be a game just not as an executable but in a project file that can only be opened in a specific game engine.

I get it if it's hard for you to answer so just tell me if I can submit my platformer character script for the godot engine lol.

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.