Cobra is a powerful interactive tool for finding defects or suspicious patterns in source code. The tool has been applied in the development and analysis of safety critical code for interplanetary spacecraft, automobile engine control software, medical device software, and cybersecurity code. This is the first comprehensive guide to Cobra, written by the tool's principal designer. It covers the tool's range of query method in detail, and provides guidance on methods for tackling complex software analysis problems. The tool is fast enough that it can be used interactively during code review or development, even on very large code archives. It can be applied to any type of textual input, with predefined settings for standard languages including C, C++, Ada, Python, Java, and HTML. Queries can be written as patterns, or expressed in a powerful inline programming language. Dr. Holzmann worked as a researcher in the Computing Science Research Center at Bell Labs, and later joined NASA's Jet Propulsion Laboratory in Pasadena, CA, to found a new Laboratory for Reliable Software, that was influential in improving the software development process at JPL. His work was recognized with the ACM System Software Award in 2001, and NASA's Exceptional Engineering Achievement Award in 2012. He was elected to the US National Academy of Engineering in 2005.