@xpy said:

I would like to make a search for directors, but I have to filter my results after I get the response from the people endpoint,
that way sometimes there are no director included in my searches for e.g. the first three letters that I type, but they appear on the fourth.
Is there a way to also filter by the known_for_department field?

No, using get/search/person it is not possible to filter by known_for_department.

Is there a plan for it to be possible in the future?

@xpy said:

Is there a plan for it to be possible in the future?

I do not think so.
I didn't find anything on To-Do Trello.
https://trello.com/b/bVlsp6wz/api
https://trello.com/b/k34aFUme/web

Can I create a local subsets of the results with the filters that I want?

@xpy said:
Can I create a local subsets of the results with the filters that I want?

I believe only Travis Bell, the Administrator, can answer your question.

Is Travis Bell pinged by the mention or do I have to reach him?

He read the forums, especially this one.

Hi @xpy, this is not possible at this time. This is the first time anyone has asked for this so I've created a new ticket to track this request here.

Thanks!

Do I break any rules if I create local subsets of the results though?

Nope, feel free to do so. As always though, just be sure to attribute TMDB as the source of the data.