Note: This site is not up to date right now! The site needs an update to handle the different forms of Pokémon. But unfortunately I have currently no time for that. Until then, please use our spreadsheet which I have already updated: Pogomoves Google Spreadsheet
Effectiveness Changes 21.06.2017
With the new gym update Niantic also changed the type effectiveness. This are the new values:

So on the move info page you can see now "Good against", "Weak against" and "Ineffectiv against". On the Pokémon Info page the new STAB value is implemented and the "Type Effectiveness against" is updated. The damage multiplier is calculated directly now. For more information look in the Notes on a Pokémon Info page. On top of that the Gym Offense Ranking is updated with the new values, if you choose a defender.