Coan is a software engineering tool for analysing preprocessor-based configurations of C or C++ source code. Its principal use is to simplify a body of source code by eliminating any parts that are redundant with respect to a specified configuration.

Coan is most useful to developers of constantly evolving products with large code bases, where preprocessor definitions and #if-directives are used differentiate progressive releases or parallel variants of the product. In these settings the upkeep of the product's configuration tree can become difficult and the incidence of configuration-related defects can become costly. Coan can largely automate the maintenance of preprocessor-based configurations and the investigation of configuration-related questions.