Version: 3.x

Slot Validation Actions

A slot validation action is a special type of custom action, designed to handle custom extraction and/or validation of slot values. This can be used to validate slots with predefined mappings or extract slots with custom mappings.

You can do custom extraction and validation of slot values by writing custom actions in three different ways.


You can use the action_validate_slot_mappings action to define custom extraction and / or validation of slots that can be set or updated outside of a form context.

This action is called automatically at the end of the default action action_extract_slots, so the name must not be changed. If you are using Rasa SDK, you should extend the Rasa SDK ValidationAction class. If you are using a different action server, you will need to implement an action class with equivalent functionality to the Rasa SDK class. Please see the action server docs for details.

With this option, you do not need to specify the action key in the custom slot mapping, since the default action action_extract_slots runs action_validate_slot_mappings automatically if present in the actions section of the domain.

validate_<form name>

Custom actions named validate_<form name> will run automatically if the form it specifies in its name is activated. If you are using Rasa SDK, the custom action should inherit from the Rasa SDK FormValidationAction class. If you are not using Rasa SDK, you will need to implement an action or action class with equivalent functionality to the FormValidationClass in your custom action server. Please see the action server docs for details.

Regular Custom Action

You can use a regular custom action custom action that returns slot events for custom slot extraction. Use this option if neither action_validate_slot_mappings or validate_<form name> meet your needs. For example, if you want to reuse the same custom action explicitly in a story or rule, you should use a regular custom action for custom slot extraction. A slot validation action should only return slot and bot events. Any other event type will be filtered out by the default action action_extract_slots. The name of the custom action must be specified in the action key of the relevant custom slot mapping in the domain. Note that the action name must be listed in the domain actions section too.

Using different actions for extraction and validation

You can use both a regular custom action and action_validate_slot_mappings together to extract and validate a slot. For example, you can specify a regular custom action as the action for a custom slot mapping, and also add validation logic for the same slot to action_validate_slot_mappings. The custom action specified in the custom slot mapping will be called first, and action_validate_slot_mappings will be called afterwards.