book of secrets; inside information; trade secrets
Refers to a document or knowledge containing confidential tips, tricks, or know-how, often in business, crafts, or specialized fields. Idiomatic, derived from the legendary Chinese military text.
He is said to have the inside secrets of that industry.
study guide; crib; answer key
Commonly used for supplementary materials that reveal answers, solutions, or effective study methods for textbooks or exams. Often has a slightly informal, 'cheat sheet' connotation.
I borrowed a study guide from a friend before the exam.
This reference book is practically a crib.