There is a method in org.eclipse.jetty.server.Response: public void sendError(int code, String message)
When message is not null it gets placed in both the title and body of the page. In other servers, such as Tomcat, the default behavior is to change the body but leave the title unchanged. For example, Tomcat has a property org.apache.coyote.USE_CUSTOM_STATUS_MSG_IN_HEADER which defaults to false. It may be worth adding such an option in Jetty, or changing the behavior of sendError such that the message is not inserted into the title.