In six years of studying 3 languages, this is my favorite studying tactic.

This tool converts pinyin and tone numbers into pinyin with tone marks above the correct vowels. It's fully written in Javascript, so it's very fast and doesn't require page loads.

The opening salvo in a debate over the romanization of road signs. A scrappy debate in the comments, too.

"Writing Chinese words with the Latin character set and neglecting tone marks is the equivalent of writing English words with dots in place of the vowels."