Google Web Toolkit uses Apache Ant to start a web container, either Jetty or Tomcat, along with the GWT application. Thus, to enable JReble for GWT in development mode, one should set ANT_OPTS environment variable accordingly.

Go to the GWT project directory, and create run-jrebel.cmd file with the following content:

    @echo off
    set ANT_OPTS=-javaagent:$AGENT_PATH_WIN
    ant devmode

Now use run-jrebel.cmd to run your GWT application in development mode with JRebel enabled.