Here's a small example. I feel like this is something that I should be able to do (downgrade an iron axe to a wooden hoe), but the create button is greyed out even though stats change, but no reason is given as to why. If a module can't use this material in this slot, it shouldn't show the stats of what the supposed material would calculate to (I think it's a bit misleading for new people). This has happened in a few situations, but this is one of the most basic examples. It would be nice to show a message in red saying why the item can't be made ("Invalid material") and such.

I love Tetra! Keep it up 👍

It turns out that all materials that require any other tool than a hammer does not indicate this and vanilla items did not count as tools in this case. Stats are only intended to show up if it's a possible craft and if you lack the proper tool that should also show. This problem seem to have been around for a while, thanks for reporting the issue. Fix will be part of next release, and I'm happy that you like it!

This has been fixed in 0.15.1.