Mikkolek

Thank you so much, this fixed the problem!

You need to unzip it. Mods always have a ".jar" extension

If I understand capabilities correctly, their state is supposed to be saved when the world is quit and reload when it's open again, but in my case, the capability just resets to 0 when I reload the world. I've just started getting into modding, so I'm sorry if I made some really simple mistake, but I can't figure out what I'm doing wrong. I based my capability mainly on this tutorial from McJty: https://youtu.be/W3SS7yP4B2s and I also read the page about capabilities on the forge docs, but it seems to be quite outdated. You can find my test mod here: https://github.com/Mikkolek/TestCapabilitiesMod. I also made a simple command called "/devmode" to check the capabilities it's state and change it.