A custom host errors definition service is provided. The custom host errors definition service can create separate endpoints through which different customers can define custom host errors for one or more host computing systems, which might operate in a distributed execution environment. A custom host error definition can specify one or more host computing systems, one or more system components of the one or more host computing systems, one or more attributes, one or more error conditions for the one or more attributes, and one or more actions to perform as a result of the error conditions being satisfied. The error conditions can be, but are not limited to, threshold conditions, component failure conditions, missing hardware conditions, degraded hardware conditions, system firmware failures, incorrect firmware conditions, and the like.