Our difficulty ratings are powered by our community. Any user can grade their completed books by comparing two books at a time - either choosing one book to be more difficult or deeming both books to be about the same difficulty.
For example, if you've read both よつばと！ and ふらいんぐういっち, you'll be prompted to compare them as shown below:
While we recommend that you think of the levels as relative levels (a level 15 book is harder than a level 5 book), we do showcase a very approximate mapping to the JLPT proficiency levels, in order to help users quickly find content they might be challenged by. However, this is just a best guess - don't be afraid to try something 'above' or 'below' your JLPT level.
|Levels 0-9||Beginner, ~JLPT N5|
|Levels 10-19||Beginner, ~JLPT N4|
|Levels 20-29||Intermediate, ~JLPT N3|
|Levels 30-39||Intermediate, ~JLPT N2|
|Levels 40-49||Advanced, ~JLPT N1|
|Levels 50+||Advanced+, ~JLPT N1+|
There is no formal criteria. Rather, each user grades the difficulty as they see fit - some users will deem strange vocabulary as more difficult than complex grammar or vice versa. This hopefully averages out to a general language learner's perspective.
Each book is created with an initial estimated level (chosen by our team or the user who requested the resource). Until the book has been graded a few times, the difficulty level will fluctate significantly. These temporary grades are marked by '??'.
Some categories of books (currently only textbooks) are excluded from user gradings, with the level simply specified by our team. It's nonsensical to compare a textbook vs a manga in terms of difficulty. We do want to incorporate user gradings of textbooks at some point, but currently we do not.
Without our community grading books, this wouldn't be possible. Thank you so much! Additionally, if you have any large disagreements with a particular rating, please contact us!