I'm running an add_filter function on the_content and I need to run the same function on the category description.
Does something like that exist or do I need to create a custom function for it?
Sure, hook it right onto
Here's an example:
Didn't test it but based on the Codex it should work.
See the Codex for more info: http://codex.wordpress.org/Plugin_API/Filter_Reference#Category_and_Term_Filters