It's recommended you use the wordpress developer reference workflow as It's more up-to-date with the most recent WordPress functions
Here is a workflow for WordPress developers that searches all the functions in the WordPress function reference.
After searching the functions you can go directly to the correct Codex function page.
It searches a list (that comes with the workflow) with all the functions in the function reference. Update this list from time to time with the keyword "wpfrupdate". Sometimes It can take a while before you see the message that the functions are updated.
This makes looking up functions very fast because no internet connection is needed for looking in the function list.
Here's what it looks like when searching for functions with the keyword "wpfr".
You can download it here: FunctionReference.alfredworkflow