This pinyin converter turns pinyin with numbers into pinyin with tone marks.

Enter pinyin followed by numbers 1-4 represent the Chinese tones.  For neutral tone words, either type 5 or no number at all.  Use the letter “v” for the “ü” character.  Press convert to add the tones.

Now supports apostrophes! (e.g. Xi1an1 -> Xī’ān)
Suggestions? Comment here.