How aggregatable fields are defined in Kibana

[Alexandros888]

Hello i created an index and i saw that even some string or boolean fields are aggregatable.

That helped a lot because i created aggs during alert creation even on those string and boolean fields.

My question is the following:

When an index is created how you can specify from the beginning which fields to be aggregatable so that you can use the aggs function later on them when you create alerts?

[wylie (Wylie Conlon)]

Keyword fields are aggregatable by default, but text fields are not. It maps to whether the field uses doc_values which is how keyword fields work