Congratulations is what you say to somebody who has succeeded or had good news. Congratulations on the new job. Congratulations to the winners.
It is always plural and it takes on before the thing: congratulations on passing, congratulations on the baby. Congrats is the informal short form and is very common in messages. Note that in some cultures it is normal to congratulate somebody on a birthday, and in English it is not — happy birthday is the phrase, and congratulations there would sound odd. And congratulations on getting married is fine while congratulating the bride was once considered rude, which is a rule almost nobody now keeps.
1phrasecongratulationsSaid to somebody who has succeeded or had good news.
“Congratulations on the new house.”
synonyms: congrats, well done
2nounexpressionsExpressions of pleasure at somebody's success.
“Congratulations poured in all afternoon.”
Too few real examples of this word to estimate which sense is commonest.
congratulations is an expression of praise.
Also accepted in games: congrats