Players cannot purchase hacked Dragon City gems on Facebook. However, they can acquire free hacked Dragon City gems and related items from other websites, such as DragonCityHackOnline.com.
According to DragonCityHackOnline.com, their service allows users to get free food and/or gems for their Dragon City dragons. The website allows users to select the amount of food and gems they would like. No additional software is required in order to attain these in-game items.
Additionally, although players cannot purchase Dragon City gems on Facebook, they can acquire them for free. For example, Dragon City Hackz provides users with free hacks for Dragon City, including hacks for gem codes.