So, now Chrome (35+) and FireFox don't support GWT "classic" DevMode, I've managed to run drools-wb in SuperDevMode. The "classic" DevMode will not be supported in GWT 2.6: http://www.gwtproject.org/release-notes.html#Release_Notes_2_6_1 Here's my findings on how to configure your webapp, IDE and run (or debug) the damn thing. These instructions are for IDEA (NetBeans will probably follow a similar route). (1) Create a regular GWT Launcher: ​ (2) Create a new GWT Launcher for SuperDevmode: ​ (3) Add the following to your webapp's gwt.xml (module) file: <!-- SuperDevMode --> <add-linker name="xsiframe"/> <set-configuration-property name="devModeRedirectEnabled" value="true"/> <set-property name="compiler.useSourceMaps" value="true"/> <set-configuration-property name='xsiframe.failIfScriptTag' value='false'/> (4) Launch your regular webapp (the "classic" GWT Launcher): ... <tick>, <tock>, <tick>, <tock> while it compiles and launches... ​ (5) Launch the SuperDevMode code server (the "SuperDevMode" GWT Launcher): ... <tick>, <tock>, <tick>, <tock> while it compiles and launches... ​(6) Drag the "Dev Mode On" and "Dev Mode Off" buttons to your bookmark bar (as advised) - but we don't normally read these sort of things, right! ;) (7) Go back to the webapp's browser tab (8) Click on the "Dev Mode On" bookmark you created in step (6) ​ (9) Click on "compile" ​ (10) Delete the "codesvr" part of the URL and press enter (dismiss the popups that appear; which ones depends on what browser your GWT module targets; e.g. I had to dismiss a popup about using Chrome but the GWT model targets FireFox). ​(11) Done! ​ (12) What's that? You want to debug your application?!? This isn't too bad. Just launch both your "classic" GWT Launcher in debug mode and the "SuperDevMode" GWT Launcher in normal mode. Server-side code needs break-points in IDEA, and client-side break-points need to be added using Chrome's Developer Tools (you'll need to make sure "sourceMaps" are enabled, but this appears to be the default in Chrome 35). Accessing Chrome's debugger: ​ Debugging: ​ Simple! It takes a bit of getting used to debugging client-side stuff in Chrome, and server-side stuff in IDEA, but it's not terrible (although don't expect to be able to introspect everything in Chrome like you used to in IDEA). I hope this helps (probably more so as others find "DevMode" stops working for them.... and when we move to GWT 2.6.1 --- for IE10 support --- so it is coming sooner than later). Cheers, Mike