To obtain free gems in Dragon City, win against seven teams in player-versus-player combat or win a battle against a themed team in the stadium. Other ways to win free gems are leveling up, inviting friends, collecting a reward, completing parts of The Dragon Book or receiving them at random.
Some actions creates more gems than others. For example, every time a player levels up, he receives a single gem. On the other hand, if a player defeats seven teams in combat, then he receives two gems or three gems if he is playing the mobile version of the game. Players also receive two gems for winning against a single themed battle team in the stadium.
The Monday reward bonus gives players a one in three chance to receive five gems if they select the right reward. Players also receive five gems when a person they invite to the game accepts their request. A player only receives the bonus if the friend he invited plays beyond the tutorial section of the game.
As players progress through the game, they receive two to 18 gems based on the parts of The Dragon Book they complete.
The largest number of gems players can collect for free comes from the Deus Daily Bonus, which is a luck-based game that gives out 50 gems.