Java code can be annotated with formal specifications using the Java Modelling Language (JML). Previous work has provided IDE plugins intended to help write JML, but mostly for the Eclipse IDE. We introduce IntelliJML, a JML plugin for IntelliJ IDEA, with a focus on ease of use and maintainability. Features such as syntax, semantic, and type checking, as well as syntax highlighting and code completion are integrated into the plugin. The plugin can also be extended in the future to add more features. The source code for the plugin can be found at https://gitlab.utwente.nl/fmt/intellijml.