Validate slot without using form

As stated in the topic… Is it possible to validate a slot, that is not used in any form? Create like slot_validate method, that validates specific slot? I figured out, that I can create a custom action and rule that runs it, when the slot is set, but… Is this the only approach? Nothing simpler?

Calling a custom action would be the easiest approach. Rasa doesn’t require the action server to be written in python or a programming language. You could create an action server with another language or tool that accepts the REST endpoint but I’m sure this is much more of an undertaking than writing a python validate function.