Managing conversation flow with a fallback intent on Amazon Lex

Ever been stumped by a question? Imagine you’re in a business review going over weekly numbers and someone asks, “What about expenses?” Your response might be, “I don’t know. I wasn’t prepared to have that discussion right now.”

Bots aren’t fortunate enough to have the same comprehension capabilities, so how should they respond when they don’t have an answer? How can a bot recover when it doesn’t have the response? Asking you to repeat yourself could be quite frustrating if the bot still doesn’t understand. Perhaps it can pretend to understand what you said based on the last exchange? That might not always work and could also sound foolish. Maybe the bot can admit its limitations and tell you what it can do? That would be acceptable the first few times but can be suboptimal in the long run.

There is no single correct way. Conversation repair strategies vary by the kind of experience you’re trying to create. You can use error handling prompts. The bot would try to clarify by prompting “Sorry, can you please say that again?” a few times before hanging up with a message such as, “I am not able to assist you at this time.”  Building on the sample conversation above, let us first build a simple chatbot to answer questions related to revenue numbers. This bot answers questions such as “What’s the revenue in Q1?”, “What were our sales in western region?” The Lex bot contains only two intents: RegionDetails and QuarterDetails. With this bot definition, if someone were to discuss expenses (“How much did we spend last quarter?”), the bot would go through the clarification prompts and eventually hang up. You couldn’t intervene or execute business logic. The conversation would resemble the following:

Starting today, you can add fallback intent to help your bot recover gracefully in such situations. With a fallback intent, you can now control the bot’s recovery by providing additional information, managing dialog, or executing business logic. You can control the conversation better and manage the flow for an ideal outcome, such as the following:

Configuring the fallback intent

You can configure your fallback intent by completing the following steps.

  1. From the Amazon Lex console, choose Create intent.
  2. Search for AMAZON.Fallback in the existing intents.

See the following screenshot of the BusinessMetricsFallback page:

If you have any clarification prompts the Fallback intent will be triggered after the clarification prompts are executed. We recommend disabling the clarification prompts. Hang up phrase are not used when Fallback is configured. See the following screenshot of the Error handling page:

  1. Add an intent ContactDetails to collect the email ID.

This is a simple intent with just the email address as a slot type. Please review the bot definition for intent details.

  1. Add an AWS Lambda function in the fulfillment code hook of the fallback intent.

This function performs two operations. First, it creates a task (for example, a ticket entry in a database) to record your request for an operator follow-up. Second, it switches the intent to elicit additional information, such as your email ID, so that a response goes out after an operator has processed the query. Please review the Lambda definition for code details.

With the preceding bot definition, you can now control the conversation. When you ask “How much did we spend last quarter,” the input does not match any of the configured intents, and triggers the fallback intent. The fulfillment code hook of the Lambda creates the ticket and switches the intent to ContactDetails to capture the email ID.


This post demonstrated how to have better control of the conversation flow with a fallback intent. You can switch intents, execute business logic, or provide custom responses. For more information about incorporating these techniques into real bots, see the Amazon Lex documentation.



About the Author

Kartik Rustagi works as a Software Development Manager in Amazon AI. He and his team focus on enhancing the conversation capability of chat bots powered by Amazon Lex. When not at work, he enjoys exploring the outdoors and savoring different cuisines.





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