From the PDF:
Carnival Row offers a dark, fantastic world that calls back to the styles and social graces of Edwardian London, in a society still shakily recovering from a conflict that resembles European colonial wars — but with industrialized destruction that resembles World War I.
Let this supplement function as your guide: it is a reference book to help you build and create your own stories in the world of Carnival Row.
If an episode introduces something that contradicts what you have built into your narrative, never fear! Once you pick up the dice and begin to play, it becomes your world. You can adapt the lore to serve the story your group tells together.
Provided within these pages is information to build human and fae characters; a cultural overview and a history of the war that now embroils the Fae homelands, The Burgue, and the Pact; and the details of the city of The Burgue and denizens thereof. This supplement uses the Cypher System by Monte Cook Games and the Cypher System Rulebook is required to play.