Hi, I am building a JVM agent that needs to programmatically register a logback appender to intercept logging messages from a web-application(s) running on the given JVM. By using the JVM agent I can avoid modifying the web-application's code & configuration. To make this work, I need to use byte-code instrumentation and in the class-loading phase modify some logback class(es) and inject my code that instantiates my (interception) appender and adds it to list of appenders associated with the root logger. What would be the best logback API class and method to instrument? Ideally it should be a class and method that: . Is called once upon every logback (re)initialization . Has been present in older logback versions. . Is public, stable and is not likely to disappear in future logback releases. Thank you, Jan