The Eclipse AspectJ development tools (1.4.1) seem to be finicky when it comes to applying changes to aspects. If you uncomment a declare warning, for example, the change will not be noticed and will not trigger a rebuild even after you save the file. You must make a more substantial change elsewhere in the aspect file. Also, the builder seems to ignore changes to all aspect files after you add AspectJ nature to a Java project . I found myself having to do manual cleans to get my AspectJ changes to take.