Quick answer
Молоде́ц!
maladyéts — one person молоде́ц, several молодцы́ — and no gender change
The options
Молоде́ц!Well done! — to one person
Молодцы́!Well done! — to several
Отли́чно!Excellent!
Так держа́ть!Keep it up!
Ты молоде́ц, что сказа́л.Good of you to say so.
One form for everyone
Молоде́ц does not change for gender — a woman is also молоде́ц. The only change is the plural молодцы́, with the stress on the ending.
Who can say it to whom
It works downwards and sideways: to children, students, friends and colleagues. Said to your boss or to someone much older, it can sound patronising — there отли́чная рабо́та or о́чень здо́рово is safer.
What you hear back
Спаси́бо!Thanks!
Да ла́дно.Oh, come on.
Стара́лся / стара́лась.I did my best.
Typical mistakes
Молоде́ца! — to a woman
Молоде́ц!
The word has no feminine form.
Молоде́цы!
Молодцы́!
The plural shifts the stress to the ending.
Check yourself
How do you praise a group?
Plural with end stress: молодцы́.