Keen Item 13

Pathfinder Core Rulebook (Second Edition), page 584

Category Runes; Price 3,000 gp; Usage etched onto a piercing or slashing melee weapon

The edges of a keen weapon are preternaturally sharp. Attacks with this weapon are a critical hit on a 19 on the die as long as that result is a success. This property has no effect on a 19 if the result would be a failure.