How text is flipped
There is no way to rotate plain text. The generator does two things instead. First, it replaces each letter with a character that looks like that letter turned upside down, such as ǝ for e or ɐ for a. Then it reverses the order of the characters, so the message reads correctly when you turn your screen around.
Many of these replacement characters come from the International Phonetic Alphabet, which already contains rotated letter shapes for writing sounds.
Why some letters look a little off
Not every letter has a true upside-down twin in Unicode. Some are filled with the closest lookalike, and some letters look the same either way (like o, s, x and z). Capital letters have fewer good matches than lowercase letters, so the Upside Down Lowercase style often gives the cleanest result.
Backwards text
The Backwards style only reverses the order of the characters without changing them, so “hello” becomes “olleh”. It is useful for puzzles and secret messages. It does not mirror letter shapes.