D&D 5E Ability cap of 20?

[asorel]

The stat books in the DMG (all of which are Legendary items) each raise a stat by 2 and the stat maximum by 2. Theoretically, this means infinite stats. However, I'd recommend as a house rule a hard cap of 30 for stats even with the aid of magic. This puts the character on par with the strongest and most powerful monsters in the game.

Maybe one could make stats above 30 the realm of divine beings.

That actually sounds like it could be an interesting plot hook. Maybe by trying to raise, say, your Intelligence score above 30 would alert the God of Knowledge, who would take it as an official challenge to his or her power. This could lead to challenging the player to some sort of test, in this case perhaps a battle of wits. If the god is suitably impressed, the player may be offered the chance to serve as a lieutenant of this god, in this case as the god of magic, or writing, etc. If the player manages to beat the god completely and unequivocally, the player replaces that god completely.

 

[lall]

Per the DMG, at ECL 20, the DM can give PCs an epic boon for every 30,000 XP they earn above 355,000 XP. Or, in place of an epic boon, he can let them choose a feat or ability score improvement. "The ability score can now be increased above 20, up to a maximum of 30."

 

[asorel]

Per the DMG, at ECL 20, the DM can give PCs an epic boon for every 30,000 XP they earn above 355,000 XP. Or, in place of an epic boon, he can let them choose a feat or ability score improvement. "The ability score can now be increased above 20, up to a maximum of 30."

Correct. There are also the Tome and Manual magic items, which allow a character to increase a stat by 2, once every 100 years or so. The hard cap on all of these, including the homebrew guide for monster creation, is 30.