also: かんのよい
expression, i-adjective (yoi/ii class)
quick on the uptake; perceptive; intuitive
Describes a person who grasps situations, hints, or unspoken things quickly. Often used for someone with good instincts or street smarts.
彼は勘のいい人だから、説明しなくてもわかるだろう。
He's quick on the uptake, so he'll probably understand without an explanation.
勘のいい読者なら、この伏線に気づく
A perceptive reader should notice this foreshadowing.
Phrase composed of 勘 (intuition, sixth sense) + の (possessive particle) + いい (good). The combination literally means 'of good intuition' and functions as a set adjectival expression.