Validate Slot Values

Slot validation lets you create validation rules for your slot values. Alexa can then check the user's response against these rules and prompt the user if the user provides an unacceptable value.

• Understand slot validation
• Configure a slot with validation rules
• Use multiple validation rules for a slot
• Delegate the dialog to Alexa to use the validation prompts
• Validation rules
  • Compare to the values and synonyms defined for a custom slot type
  • Compare to a fixed set of values
  • Compare to a specific value (greater than or less than)
  • Compare dates or times to a specified time span
• JSON for Validation Rules
• Related topics

Understand slot validation

Slot validation provides an additional dialog model component to help you manage the conversation between your skill and the user. You can configure a set of validation rules for a slot, along with prompts to use for slot values that fail validation.

When the user fills the slot with an utterance and you delegate the dialog to Alexa, Alexa checks the provided value against your rules. If the value fails the validation, Alexa uses your prompts to ask the user for a correct value.

For example, in this dialog, the user is filling a custom Planet slot that only accepts values that match the names of planets in our solar system:

To use slot validation:

1. Define validation rules and prompts for your slots where needed. These become part of the dialog model for the skill. There are several possible rules for the different types of slots. See:
   • Configure a slot with validation rules
   • Validation rules
2. Set up your skill to delegate the dialog to Alexa.

Configure a slot with validation rules

You can define validation rules and prompts in the developer console. Alternatively, you can also specify the rules and prompts in the JSON Interaction Model Schema.

To define validation rules:

1. In the left-hand navigation, find the intent and its list of slots, then click the slot name.

   Alternatively, from the page for a particular intent, find the slot in the Intent Slots section below the Sample Utterances and click the Edit Dialog link.

2. Under slot type field, select Validations.
3. Under Create Validation Rule, select the rule you want to use and click the plus.
   • The list shows just the validators that are relevant for the slot's type.
   • For details about the rules, see Validation rules.
4. Fill in any additional fields specific to the rule, such as the value to compare to. This depends on the rule. See Validation rules.

5. Below the rule, enter at least one prompt that Alexa should say to ask the user for a new value.

   You can include the slot name in curly brackets ({ }) so that Alexa speaks back the value that failed validation.

6. Be sure to save and build the interaction model.

Use multiple validation rules for a slot

You can create multiple validation rules for a slot. The rules are checked in the order in which they are shown in the developer console or listed in the JSON. If a value fails a rule, Alexa stops checking and responds with the prompt to correct the value. In a set of multiple rules, a later rule is checked only when all preceding rules have passed.

This means that you can define rules to provide smarter responses depending on the user's mistake. For example, suppose your skill provides facts about planets and uses a custom slot type with the planets of the solar system. You could use a single validation (Accept only Slot type's values and synonyms) to only accept the planet names and provide a generic prompt like "{Planet} is not a planet. Please tell me a planet in our solar system."

However, you know that users might ask about other objects in the solar system that are not planets. Rather than using this generic prompt, you could set up an additional validation to reject these specific values (Reject only a set of values) with a more specific prompt before applying the more generic validation. For example, you could define these rules for the Planet slot:

• Reject only a set of values with the values "the sun", "sun", and "our sun". Prompts:
  • "While the sun is part of our solar system, I can only answer this question for planets. Please tell me a planet."
  • "We don't think of the sun as having weather, exactly, so please tell me a planet instead."
  • (similar prompts showing that Alexa understands the value provided)
• Accept only Slot type's values and synonyms. Prompts:
  • {Planet} is not a planet. Please tell me a planet in our solar system.
  • (similar generic prompts that repeat back the incorrect value)

Delegate the dialog to Alexa to use the validation prompts

Alexa uses your slot validation rules when you delegate the dialog. There are two ways to delegate to Alexa:

• Delegate automatically. In this case, Alexa automatically checks the slot values and uses the prompts defined in the dialog model as needed. Alexa sends your skill a single IntentRequest once the dialog is complete.
• Delegate manually. In this case, Alexa sends your skill an IntentRequest for each turn of the conversation. You return the Dialog.Delegate directive if the dialog is not complete. This tells Alexa to take the next step in the dialog.

For details about delegating the dialog, see Delegate the Dialog to Alexa.

You can use slot validation with both required and non-required slots. This lets you validate optional values if they are provided, but not force the user to fill those slots:

• If the user invokes the intent with no value for a non-required slot, Alexa accepts the blank slot value and does not perform any validation or elicitation.
• If the user does provide a slot value, Alexa validates the slot value according to the slot validation rules and uses the prompts as needed.
• For a required slot, Alexa elicits the slot value if necessary, and then does the validation in a subsequent step.

For more about ways to manage the conversation when you have a dialog model, see Dialog Interface Reference: About Managing the Conversation with the User.

The other Dialog directives such as Dialog.ElicitSlot do not use the slot validation rules defined in the dialog model. You must delegate the dialog either with auto delegate or Dialog.Delegate to use the rules.

Validation rules

The following sections provide details about all of the validation rules available and the slot types with which they can be used.

• Compare to the values and synonyms defined for a custom slot type
• Compare to a fixed set of values
• Compare to a specific value (greater than or less than)
• Compare dates or times to a specified time span

Compare to the values and synonyms defined for a custom slot type

This rule lets you accept only values that are explicitly defined for a custom slot type. The rule checks both value and synonyms. You can use this validation only with slots that use a custom slot type.

Compare to a fixed set of values

These rules let you either accept or reject a set of values. You can use these rules with the following slot types:

• AMAZON.FOUR_DIGIT_NUMBER
• AMAZON.NUMBER
• AMAZON.Ordinal
• AMAZON.PhoneNumber
• All built-in List Types
• Any custom slot type

The list of values in the set to accept or reject must be compatible with the slot type:

• AMAZON.FOUR_DIGIT_NUMBER: Provide a list of four-digit numbers.
• AMAZON.NUMBER: Provide a list of numbers.
• AMAZON.Ordinal: Provide a list of numbers that correspond to the ordinal values to accept. For example, to accept or reject the words "first," "second," and "third," you would provide the numbers 1, 2, and 3.
• AMAZON.PhoneNumber: Provide a list of phone numbers. Include just the digits of the numbers, no dashes or other formatting. For example: "2065551234".
• All built-in List Types. Provide a list of string slot values.
• Any custom slot type. Provide a list of string slot values.

Compare to a specific value (greater than or less than)

These rules let you accept user-provided slot values that are greater or lesser than a value you specify. You can use these rules with the following slot types:

• AMAZON.DATE
• AMAZON.FOUR_DIGIT_NUMBER
• AMAZON.NUMBER
• AMAZON.TIME slots.

The value to compare with the user's slot value must be compatible with the slot type:

• AMAZON.DATE: Specify a date in ISO-8601 calendar date format. The value must be an absolute date with the year, month, and day provided: 2018-11-08.
• AMAZON.FOUR_DIGIT_NUMBER: Specify a four-digit number.
• AMAZON.NUMBER: Specify a number.
• AMAZON.TIME: Specify a time in ISO-8601 time format. The time must include hours and minutes, for example: 14:15 (two fifteen PM).

When you use these validation rules for date and time comparisons (AMAZON.DATE and AMAZON.TIME slot types), note the following:

• "greater than" means after the date or time
• "less than" means before the date or time

For example, if you use isGreaterThan with an AMAZON.DATE slot and set the value to 2018-01-01, the slot accepts any date after January 1, 2018. Both December 31, 2017 and January 1, 2018 would fail validation. Use isGreaterThanOrEqualTo to include January 1 as a valid date.

Compare dates or times to a specified time span

These rules let you either accept or reject a date or time that falls within a particular time span. You can use these rules with AMAZON.DATE and AMAZON.TIME slots.

You can use relative and absolute dates and times to specify the start and end of the time span.

• AMAZON.DATE: Provide the start and end as either:
  • Specific dates in ISO-8601 calendar date format
  • Durations in days in ISO-8601 duration format (PnD). For example, P10D for 10 days. Note that the validation does not support durations that include other units such as months or years.
• AMAZON.TIME: Provide the start and end as either:
  • Specific times in ISO-8601 time format
  • Durations in hours and/or minutes in ISO-8601 duration format (PTnHnM). For example, PT10H for ten hours, or PT5H30M for five hours and thirty minutes.

The start and end of the time span are relative to when the user makes the request to your skill, based on the user's configured time zone. If the user's device is not configured with a time zone, the validation assumes GMT. The start time must come before the end time.

When you use a duration in days or hours, you can use a minus sign (-) to indicate time before the current time. For example, -P3D specifies three days before today. Note that this is not part of the ISO-8601 standard.

You can combine absolute dates and relative durations in the same validation. For example, set start to 2018-07-04 and end to P3D to accept a date within three days of July 4, 2018.

You can also leave either start or end blank to create an open-ended time span. For example, set start to P0D (today) and leave end blank to accept just dates today or later and reject any dates in the past.

Date examples:

Time examples:

JSON for Validation Rules

You can see and edit the JSON representation of slot validations within your dialog model in the JSON Editor. Validations for a slot are defined in the validations array in interactionModel.dialog.intents[].slots[].validations. The corresponding prompts are in prompts.

For brevity, the languageModel property is not shown. For details about the interaction model JSON, see Interaction Model Schema.

{
  "interactionModel": {
    "dialog": {
      "delegationStrategy": "SKILL_RESPONSE",      
      "intents": [
        {
          "name": "GetPlanetWeather",
          "delegationStrategy": "ALWAYS",
          "confirmationRequired": false,
          "prompts": {},
          "slots": [
            {
              "name": "planet",
              "type": "Planet",
              "confirmationRequired": false,
              "elicitationRequired": true,
              "prompts": {
                "elicitation": "Elicit.Slot.27936398519.1404759397895"
              },
              "validations": [
                {
                  "type": "isNotInSet",
                  "prompt": "Slot.Validation.154616755422.1503388152026.257948657476",
                  "values": [
                    "sol",
                    "the sun",
                    "our sun",
                    "our star",
                    "sun"
                  ]
                },
                {
                  "type": "hasEntityResolutionMatch",
                  "prompt": "Slot.Validation.154616755422.1503388152026.1155325818232"
                }
              ]
            }
          ]
        }
      ],
    },
    "prompts": [
      {
        "id": "Elicit.Slot.27936398519.1404759397895",
        "variations": [
          {
            "type": "PlainText",
            "value": "Tell me a planet and I'll give you an idea of the weather there"
          },
          {
            "type": "PlainText",
            "value": "For what planet?"
          },
          {
            "type": "PlainText",
            "value": "Tell me a planet in our solar system"
          },
          {
            "type": "PlainText",
            "value": "What planet did you want to know about?"
          }
        ]
      },
      {
        "id": "Slot.Validation.154616755422.1503388152026.257948657476",
        "variations": [
          {
            "type": "PlainText",
            "value": "While the sun is the center of our solar system, it is not a planet. Please tell me a planet."
          },
          {
            "type": "PlainText",
            "value": "Only planets have weather. Please tell me a planet"
          },
          {
            "type": "PlainText",
            "value": "We don't think of the sun as having weather, exactly, so please tell me a planet instead."
          },
          {
            "type": "PlainText",
            "value": "While the sun is part of our solar system, I can only answer this question for planets. Please tell me a planet."
          }
        ]
      },
      {
        "id": "Slot.Validation.154616755422.1503388152026.1155325818232",
        "variations": [
          {
            "type": "PlainText",
            "value": "Please tell me a planet like Earth, Mars, or Jupiter. You know, one of the nine in the solar system."
          },
          {
            "type": "PlainText",
            "value": "{planet} is not a planet -- I need one of the nine planets in our solar system"
          },
          {
            "type": "PlainText",
            "value": "I did not recognize {planet} as a planet in our solar system. Please tell me a valid planet."
          },
          {
            "type": "PlainText",
            "value": "Please tell me a planet within our solar system"
          }
        ]
      }
    ]
  }
}

Related topics

• Dialog Interface Reference
• Create the Interaction Model for Your Skill
• Create Intents, Utterances, and Slots
• Create and Edit Custom Slot Types
• Define the Dialog to Collect and Confirm Required Information
• Test Your Utterances as You Build Your Model
• Batch Test Your NLU Model
• Alexa Design Guide
• About the Alexa Developer Console
• Build Skills in the Alexa Developer Console

Last updated: Nov 28, 2023