What previous versions did it work in ? previous versions of JBoss Tools or previous versions of the wildfly server ?
In any case you should be able to add it by having the following line in MANIFEST.MF:
Then the tools should locate the websocket jar for you and add to the classpath automatically.
I think that the version that works is JBoss Tools (Kepler) 4.1.2.Final you can add in a experimental way wildfly, and I was using wildfly 8.
I added Dependencies: javax.websocket to the MANIFEST.MF file of the project but didn't work, when I add the @ServerEndpoint annotation to a class it marks error because it is not found its definition.
User on [JBIDE-18741] Java EE 7 batch API missing from WildFly classpath container - JBoss Issue Tracker wrote the following:
As a workaround, I had to add the module via Preferences->Server->Runtime Environments->Default Classpath Entries.
Will investigate asap why Max's workaround is not working