Alert; ready to act; cautious.
This idiom is usually used with the verbs stay and keep.
Готовность к действию; "на чеку".
He has been on his toes so far.
Он до сего момента был готов действовать.
It’s important for all the players on a soccer team to stay on their toes.
The successful ball player is always on his toes.
We’d better keep on our toes while we’re walking along the dark portions of this street.