Hi, I was working in a factions server with a friends and we want to make some items of kits irreparable so the players can't repair it, I don't know if is some tag yet to make this.

Just add unbreakable:true.

I like this suggestion, I'll go with both

Irreparable with /repair, an anvil or both?

Irreparable with both, or something like the nbt tag RepairCost that allows to set a custom repair cost for an item

Duplicate of #377

This has been fixed in 203d656. You can grab the fix from build 516 on the CI server.