Chinese grammar: Positive adjectives with "-ji le"极了
Just as 死了 can be used to intensify negative adjectives, 极了 (jíle) can be used to intensify positive adjectives.This is used in spoken, colloquial Chinese. 极 means "extreme" or "utmost", so using this grammar pattern takes your positive adjectives to the extreme!
It's as simple as using 极了 after the positive adjective.
Note that this structure is a degree complement (called 程度补语 in Chinese)， and one of the few that you can use after the adjective and without adding a 得.
你的 中文 好 极了。
Remember to add the 了, since this is sort of an exclamatory statement similar to 太好了. It would be incorrect without it.
× 今天 我 的 精神 好 极。
√ 今天 我 的 精神 好 极了。