Core rule · Rules Tome 2.0.8 § 105
Die rolls
Natural 20 is a critical success and natural 1 is a critical failure.
How it works
Full rule
Critical results automatically succeed or fail and cannot be changed or rerolled. A natural roll is the die result before modifiers. If an effect rerolls a roll made with multiple dice, all dice are rerolled.
At the table
Example
A natural 20 hits even when the final modifier would otherwise miss the target AC.
Watch for this
Common mistake
Bonuses do not turn another number into a natural 20, and penalties do not turn another number into a natural 1.