Pinyin is the official romanization system for Standard Mandarin. It writes Chinese syllables with Latin letters and marks the four tones, so learners and input methods can represent pronunciation without relying only on characters.
This site can add Pinyin to Chinese text and help you type tone marks. The Pinyin Writer turns tone numbers such as hao3 into hǎo.
What these tools do
Pinyin tools show pronunciation. They do not convert Simplified characters to Traditional characters. If you need both, convert the characters first, then generate Pinyin.
Pinyin is also not a translation. zhong1 guo2 tells you how 中国 / 中國 is said. It does not explain the word to someone who does not read Chinese.
Start with What is Pinyin? or open the Chinese to Pinyin converter.