The Forbidden Archive uses ratings from a now defunct site called FictionRatings.com.
K: Content is intended for general audience 5 years and older. Content should be free of any coarse language, violence, and adult themes.
K+: Content is suitable for more mature children; 9 years and older. With minor action violence without serious injury. May contain mild coarse language. Should not contain any adult themes.
T: Content is suitable for teens; 13 years and older. With some violence, minor coarse language, and minor suggestive adult themes.
M: Content is not suitable for children or teens below the age of 16. With non-explicit suggestive adult themes, references to some violence, or coarse language.
MA: Content is only suitable for mature adults. May contain explicit language and adult themes.