This guide provides best practices specifically for designing voice agents. When you design a voice agent, the goal is to help users (end-users) achieve a task without escalating to a human agent. Users should feel like they are having a natural, interactive, and cooperative conversation with the voice agent.
You should also see the general general agent design guide for all agent types, and the best practices guide for using the Dialogflow service.
Measure agent quality
To measure the quality of your agent's user experience, consider tracking the following metrics:
Misroute: how many callers ended up in the wrong place.
First call resolution: number of calls that are resolved on the first call or contact.
Average handling time: how long it takes to resolve the user's issue.
Customer satisfaction: how high your voice agent scores on a user survey.
Number of turns: how many exchanges it takes to accomplish the user's task.
User churn: how often users disengage from the conversation.
Speech recognition
The following tips can help your agent recognize end-user speech:
- Your agent should encourage the end-user to use long phrases or complete sentences. This improves recognition quality.
- Consider using a webhook to verify end-user input that may not be accurately recognized or needs to be validated.
- Use no-match events to ask the end-user to enunciate more slowly and clearly.
Conversation structure
A conversation with a voice agent is generally organized in the following sequence:
| Activity | Example | Notes |
|---|---|---|
| Opening activity | User logs in or calls your contact center. Voice agent: Hello, this is Travel Inc. How can I help you today? |
The voice agent starts the conversation with a welcome message. |
| Main sequence | User: I want to book a plane ticket. Voice agent: Ok, where do you want to go? User: Guatemala on May 19th, 9PM. Voice agent: Ok, we have booked you a ticket for Guatemala on May 19th, 9PM. |
The task is defined by the user, and the task is completed by the voice agent. The task may take several turns for the voice agent to collect all the necessary information. |
| Closing activity | Voice agent: Is there anything else I can help you with? User: No Voice agent: Ok, thanks for chatting with me! |
User is ready to finish the conversation when their request is fulfilled. |
Welcome message
When designing your opening message to the user, think about how to get to the first topic as soon as possible. The welcome message should be short and straight to the point. Some suggestions include the following:
- Answer the call with phrases like "Hello."
- Identify the voice agent with phrases like "This is XYZ Company's voice agent/assistant."
- Show availability with phrases like "How can I help you today?"
Any extra information may frustrate users and cause them to escalate to a human agent. However, you may need to extend the welcome message for legal reasons, such as informing the user that the conversation may be recorded.
Avoid information that makes the conversation sound unnatural or unbalanced. For example:
| Do | Don't |
|---|---|
| Do model the language you want your users to use. For example, if you want the user to explain things in one or two sentences, limit your voice agent to one or two sentences per turn. | Don't instruct users how to speak with phrases such as "in one or two sentences, tell me…" or "you can say things like…" |
| Do focus on the task the user wants to accomplish, and design error handling strategies in case the conversation fails. | Don't tell users what the voice agent can do with phrases like "I can help you solve complex issues." |
Conversation turn pairs
A typical conversation consists of turn pairs such as the following types of exchanges:
- question-answer, which is most common for a voice agent
- invitation-acceptance/rejection
- greetings-greetings
Sometimes, a turn pair can include extra verbiage, such as an explanation about why we need to ask a question, background information related to the question we want to ask, or a reaction to the user's answer. For example, consider the following question-answer turn pair:
Voice Agent: This will cost you $10/day. (background information/explanation) Would you like to continue adding this perk? (question)
User: Yes. (answer)
Voice Agent: Awesome! (reaction)
Also see the Fulfillment section of the general agent design best practices guide for guidelines on fulfillment placement.
Conversation repair
Conversation repair is the practice of fixing misunderstandings, mishearings, and misarticulations to resume a conversation. Repairing a conversation can help build a user's trust by showing that the voice agent is listening to their request.
Some best practices include:
Be specific and use context the user already offered in previous turns. Avoid asking obvious and redundant questions such as "I didn't catch that," "I don't understand," or "I'm having trouble."
Give the user the opportunity for self-repair, which means allowing the user to repair their turn in the way they think is best to ensure that they have agency in the conversation. Avoid phrases such as "try rephrasing" or "you can say x, y, or z."
Use the "You mean x?" structure to check for understanding.
The following table describes several examples of dos and don'ts:
| Do | Don't |
|---|---|
User: I'm traveling to Italy. Voice agent: Sorry, which country? |
User: I'm traveling to Italy. Voice agent: Sorry, I'm having trouble. Can you rephrase? Where are you going? |
User: I want to pay $80. Voice agent: You mean $80? (Repeats only the information that needs confirmation) |
User: I want to pay $80. Voice agent: Do you want to pay $80? (Repeats the redundant "want to pay" information) |
Error handling
The following section describes how to handle situations where a conversation fails.
No-Match
A No-Match event is invoked when the voice agent cannot find an intent to match what the user said.
Upon the first instance of the No-Match event, try the following:
Repeat the question to the user, but rephrase it in a shorter way to indicate the information that is missing. By focusing only on missing information, the voice agent implicitly conveys that they've listened to the rest of the user's statement.
You can add "sorry" before the restated question to indicate that something went wrong on your side.
Upon the second instance of the No-Match event, show more clearly that the voice agent is making an effort to listen. For example, consider the following exchange:
User: I'm traveling to Italy
Voice agent: Sorry, which country?
User: Italy
Voice agent: Sorry, you're traveling to which country?
No-Input
If your voice agent received no verbal response from the user, repeat the question in the same way as the first time. Upon the second instance of the No-Input event, you can rephrase the original question, but ensure that all the original components of the question are present.
Limit no-match and no-input repetitions
To avoid trapping users in a loop of error handling events, implement a No-Match/No-Input maximum of 3 for every page. Escalate users to a human agent upon the third No-Match or No-Input event.
No-speech-timeout
In situations where users need to review information or make decisions before moving on, increase the no-speech-timeout setting to give users enough time to respond.
In the following example, the no-speech-timeout setting of 2 seconds is too short for the user to read an SMS message and make a decision:
Voice agent: I've sent a text message to your device. Click on the link to learn about the travel pass. I will play music to give you time to read the text and get back to me. <2 second pause> Would you like to continue?
User: I'm still reading.
Voice agent: Would you like to add the travel pass to your plan?
Conversation techniques
This section describes techniques to help the voice agent build trust with users and make conversations run more smoothly.
Designing actionable questions
Design explicit and actionable questions for your voice agent to ask the user. For example, consider the following do's and don'ts:
| Do | Don't |
|---|---|
| Do ask open-ended questions like "When are you traveling?" which prompts the user to provide dates if they know them, or say "I don't know" otherwise. | Don't ask "Do you know your travel dates?" which only prompts a yes or no answer and is less actionable. |
| Do ask "Would you like to check the order status of another package?" | Don't ask "Would you like to continue with the order status of another package?" |
You should also prepare your voice agent for situations where the user may answer a question implicitly, as people often do in natural conversations. For example, consider the following interaction:
Voice agent: Go to Account, then click on Usage, then on Usage by line. Let me know when you get there.
User: It says I can't see data from 3 months ago or older.
The user's response implies that they successfully arrived at the target screen, but that they still needed more help. Your voice agent should anticipate such implications, instead of expecting the user to only say "I got there," or "I didn't get there."
Gaining user trust
Voice agents can show users that they are listening through the use of acknowledgements and specific details. If the voice agent provides generic answers, users may feel that the voice agent sounds unnatural.
Use acknowledgements. For example, consider the following exchange, where "No problem" is used as an acknowledgement:
User: I want to set a payment arrangement for Monday.
Voice Agent: No problem. How much would you like to pay on Monday?
Add specific details to show that the voice agent is actively listening to the user. For example, in the above exchange, the phrase "on Monday" is a specific detail that indicates the voice agent has heard what the user said.
Address the user's request as quickly as possible and exclude any unnecessary steps. In the following example, the extraneous information may cause user frustration:
User: Is there an outage in my area?
Voice Agent: We know how important it is for you to stay connected. Let's find out what's causing this issue. Please tell us the last 4 digits of the line that you're experiencing issues on. If the issue is on multiple lines, just provide one for now.
User: 1234
Voice Agent: Thanks. Let me look into next steps for this line. Now, let's get started. Temporarily disabling and then re-enabling HD Voice can do the trick... Did that work?"
Make sure the conversation between the user and voice agent is balanced. Users may feel an uncomfortable lack of agency in the conversation if the voice agent dominates the conversation. Prioritize Who/Where/What/When/How questions over Yes/No questions.
Ensure that the user's conversation transitions smoothly when they want to escalate to human agents.
Additional information
See the conversation design guide provided by the Actions on Google team.
See the Voice Playbook for the Next Billion Users.
See the Cloud Text-to-Speech SSML guide.
Read about speech acts for more information about designing actionable questions.