Autocomplete was not working for JSF tags in my Eclipse. I googled it and finally found the solution on http://www.mkyong.com/jsf2/how-to-make-eclipse-ide-supports-jsf-2-0/
The different thing I did is; I downloaded javax.faces-2.xx.xx.jar and saved in a specific folder. Then I created a user library with this jar. I did not use “jsf-api-xxx.jar and jsf-impl-xxx.jar“.