(as) bright as a button

Especially intelligent, astute, or perceptive. Ted's as bright as a button, so he'll find a solution to this problem. Of course Ellen is our valedictorian—she's bright as a button. My granddad may be old and cantankerous, but he's still bright as a button. You can't get anything past him.

as bright as a button

intelligently alert and lively. informal

There is a play here on bright in its Old English sense of ‘shiny’ (like a polished metal button) and bright in its transferred sense of ‘quick-witted’, found since the mid 18th century.