Pattern: 太 + adjective + 了 = 'too / extremely [adj]!' This is the celebratory variant - 太 amplifies, 了 marks the change-of-state / exclamation. Don't drop 了 - 太好 alone sounds incomplete.
usage
One of the most common spoken exclamations. Use it to react to good news, accept a plan, or express relief. Beginners can substitute it for 太棒了 (tài bàng le, 'awesome') interchangeably.