Session Slots vs NLU Slots


I’m a little confused about the concept of the slots used by botpress.
Why are there two kinds of slots and when is it appropriate to use session slots (slot skill) vs NLU slots?

Thanks and best regards.

Hi ChFlick,

Not sure I understand your question. The two are very much intertwined.

Have a look at this guide.

Kind Regards,


I think what confused me was the difference between slot tagging and slot filling, as the former sets data to event.nlu.slots and the latter sets data to session.slots.

When using it on my bot, I used event.nlu.slots in a bot’s response, as it was hinted in the botpress editor. The problem was that I used the the slot skill, which uses session.slots.
Additionally, the debugging feature of the emulator showed the filled slots but they did not show up in the bot’s answer, which caused even more confusion.

For me it was simply not exactly clear that these features fill different variables.

As far as I understand it now, slot filling is an enhanced feature which uses slot tagging of the NLU to get the slot information, validates it and handles the replies etc. and puts the data in the session storage.

So when using the skill, I have to access event.nlu.slots and when only using NLU slot tagging I have to access session.slots.

I hope it’s somewhat clear what my problem was.

Kind Regards,