The Mary Sue Litmus TestHolepunch's Mary Sue Litmus Test:
Ah, the Mary Sue. We can't cobble together a truly comprehensive description of what they are, exactly, but we can agree on one thing: an annoying, 'perfect' character who, through a general lack of flaws and character development, is excruciating to sit through and often makes us gnash our teeth, tear our hair, and reach for the back button. This nefarious creature can be measured and detected, so let's all grab our magnifying glasses and get classifying.
This is a subjective subject; a trait that drives one person right up the wall might fail to get any reaction from another. As you go through the list, count up the points. Each trait will register from 1-5 points, with 1 being a mild thing and 5 being a serious infraction. If a trait is not addressed at all in the story the character comes from, or is totally unknown, just ignore it. And don't worry about racking up pointsthe de-Suifier part of the test ought to restore some balance to
Mary Sue - Gary Stu TestLet's get one thing very clear: there is no score that will automatically 'make' a character a Mary Sue/Gary Stu, a high score only indicates that there might be a problem with a character. This test is for people who are worried that their characters might be Mary Sues/Gary Stus; the intention is to help people to improve their characters, NOT to make people feel bad about them. So if you like your character, that's the important thing. But if you're worried about your character, and are unsure if they need further work or not, hopefully this can help.
Mary Sue/Gary Stu test:
 They have a rare hair/fur colour
 Their eyes are an unusual colour
 This happens to be red
 Their eyes change colour
 (if a female) they have large boobs
 (if a male) they are very muscular
 They are very attractive to the opposite gender
 They are very attractive to the same gender
 They have lots of friends/no friends
 They have an unusual/unrealistic pet
 They have a guardian