Lambda-String is Java agent injecting toString method to lambdas with some meta information such as the declaration class and the declaration line. The agent form let you use it, as an add-on, while you're debugging without impacting your production environment. It works for lambda expressions and method references. Also, it supports HotSpot JRE up to Java 10, and the IBM Java Technology version 8. This is done by injecting bytecode at runtime in the Java lambda internal meta factory. To avoid any particular performance issues, the injection overhead is measured and is a part of the continuous integration test suite.