Rune Carver's Defense

Prerequisite: Fighter Subclass Rune Knight

You have discovered a rune that raises natural defenses by toughening your flesh and hardening your skin until it is on par with a Hill Giant. When etched into your body, it grants the following abilities:

Increase your Strength or Constitution score by 1, to a maximum of 20.
While you aren’t wearing armor, you can calculate your AC as 13 + your STR modifier. You can use a shield and still gain this benefit.

Basically, it swaps STR for DEX in the AC equation, and sets your minimum AC to 13. A 20 STR rune knight will have an 18 AC.

One thing to consider is that STR is easier to boost beyond 20 than any other stat. Belts of Giantkind can get it up to 29. This would still just be 22 which isn't game-breaking, but being able to max out your attack and defense stat way beyond 20 with a single item is a very strong benefit. Basing it on CON instead might be less exploitable.

That’s an excellent point. I’ve switched it over to CON in my home brew. Thanks!