Two websites useful in learning about the traits of Naruto characters (besides by watching the TV show or by reading the manga) are TVTropes and The Narutopedia as of 2015. Both of these sites provide comprehensive written information about each character, how they interact with others and how they fit into the world.
Narutopedia is a wiki for the Naruto franchise. It provides information on the characters in the TV show, movies, manga and live-action adaptation, and it also explains the differences in characterization and actions between each of them. The character page allows one to navigate through the many characters presented in this franchise. The character pages are comprehensive and provide each character's history, personality, abilities and appearance. It provides more information overall compared to TVTropes.
TVTropes similarly provides information on the characters; however, this information is usually presented in the form of how their traits relate to tropes. For instance, Naruto uses the shadow clone jutsu, a technique that allows him to create multiple physical copies of himself. This is less flashy than many of the other techniques in the series but is incredibly useful. For this reason, TVTropes lists his ability under the title of its trope called Boring but Practical. This may be more useful than the Narutopedia for finding specific traits of characters.