Wiktionary
sharp as a tack
a. (context simile colloquial English) very intelligent
Usage examples of "sharp as a tack".
Thats right, its a waste of time worrying about himhes sharp as a tack, she said, and casually shifted her weight from the left leg to the right.
Asagao was quiet, gentle, and-the neighborhood discovered-sharp as a tack.
He thought, again, that while Gunny was still sharp as a tack, he seemed to be losing the edge just a hair.
A grand girl, yes, but as sharp as a tack and no friend to him—.
Bright young lawyer, sharp as a tack, hard worker, Georgetown Law School, handsome young man with real character, and he said he was always looking for new talent.
She's over ninety and sharp as a tack, but it's too much to ask her to come to the city in all this heat.