Best Practices

Tips for writing effective prompts and instructions for your voice AI agents

Writing good agent instructions is the most important factor in how well your AI phone agent performs. These best practices will help you create agents that handle calls naturally and accurately.

1. Be Specific About Your Business Context

Give your agent a clear identity and purpose. Include your business name, what you do, your hours of operation, and the types of calls the agent should expect. The more context you provide, the better the agent can handle unexpected questions.

Instead of “Answer calls for my business,” write something like “You are the front desk receptionist for Sunrise Dental, a family dentistry practice open Monday through Friday 8am to 5pm. Most callers will be patients scheduling or rescheduling appointments.”

2. Always Ask Callers to Spell Out Email Addresses

Speech-to-text engines frequently misinterpret email addresses because they contain unusual word combinations, numbers, and symbols. Always instruct your agent to ask callers to spell out their email address letter by letter, and to repeat it back for confirmation.

Include a line like this in your agent instructions:

When collecting an email address, always ask the caller to spell it out
letter by letter. After they spell it, repeat the full email address back
to the caller and ask them to confirm it is correct before proceeding.

3. Define What the Agent Should NOT Do

It’s just as important to tell the agent what to avoid as it is to tell it what to do. Specify topics the agent should not discuss, promises it should not make, and when it should transfer to a human instead of trying to handle something itself.

For example: “Do not provide pricing estimates. Do not diagnose medical conditions. If a caller is angry or requests to speak with a manager, transfer the call immediately.”

4. Structure Transfer Rules Clearly

When configuring call transfers, use a consistent format that maps caller intent to a specific destination. This helps the agent make accurate routing decisions without ambiguity.

If the caller wants to speak with someone in sales, transfer to ext:1002
If the caller wants billing or account help, transfer to ext:1005
If the caller asks for the owner by name, transfer to ext:1001
If you are unsure where to transfer, take a message instead.

5. Write Instructions in Natural Language, Not Code

Your agent instructions are processed by a language model, not a rule engine. Write them as clear, conversational instructions — the way you would brief a new receptionist on their first day. Avoid programming-style syntax, conditional logic trees, or overly technical formatting.

6. Include a Fallback Strategy

Not every call will fit neatly into your expected scenarios. Tell the agent what to do when it doesn’t know the answer or when a caller’s request falls outside its capabilities. Good fallback strategies include taking a detailed message, offering to have someone call back, or transferring to a specific person.

If you don't know the answer to a question, say "That's a great question.
Let me have someone from our team get back to you with the details."
Then collect the caller's name, phone number, and a brief description
of their question.

7. Keep Greetings Short and Natural

Long, scripted greetings feel robotic and waste the caller’s time. Keep your greeting to one or two sentences. The agent should identify itself and the business, then ask how it can help.

Good: “Thanks for calling Sunrise Dental, this is Ava. How can I help you today?”

Avoid: “Thank you for calling Sunrise Dental, your premier provider of comprehensive family dental care services in the greater metropolitan area. My name is Ava and I am an AI-powered virtual assistant here to help you with scheduling, general inquiries, and more.”

8. Use Phonetic Spelling for Tricky Pronunciations

Voice AI agents pronounce words based on how they’re written, which can lead to awkward-sounding names, street addresses, medical terms, or brand names. If your agent consistently mispronounces a word, add the phonetic spelling directly in your instructions so the agent says it correctly.

Include a pronunciation guide in your agent instructions like this:

When saying the business name, pronounce it "Tell-ZEE-no" (not "Teh-LEE-no").
The doctor's name is Dr. Nguyen — pronounce it "Win."
Our street address is on Tchoupitoulas — pronounce it "Chop-ih-TOO-lus."

You can also spell out tricky words phonetically inline wherever they appear in your instructions:

You are the receptionist for Acai (ah-sah-EE) Wellness Studio,
located at 450 Dequindre (deh-KIN-der) Road.

Test pronunciations using the Test Agent playground after making changes. Different voice models may handle the same phonetic hints slightly differently, so always verify with a test call.

9. Include FAQs for Information Not on Your Website

Your agent can reference your website through the Knowledgebase Links field, but many common caller questions involve details that aren’t published online — things like parking instructions, insurance policies, cancellation fees, or internal processes. Add an FAQ section directly in your agent instructions to fill these gaps.

Frequently Asked Questions:

Q: Where do I park?
A: We have a free parking lot behind the building off 3rd Street.
   Street parking is also available on Main Street with a 2-hour limit.

Q: Do you accept walk-ins?
A: We accept walk-ins on weekdays only, subject to availability.
   Weekends are by appointment only.

Q: What is your cancellation policy?
A: Appointments can be cancelled or rescheduled up to 24 hours in
   advance at no charge. Cancellations within 24 hours are subject
   to a $50 fee.

Q: Do you accept insurance?
A: We accept most major PPO plans. We do not accept HMO or Medicaid.
   If you're unsure about your plan, call us and we can verify your
   coverage before your visit.

This is especially useful for questions that come up frequently on calls but aren’t covered on your website. Review your call transcripts to identify recurring questions and add them to your FAQ list over time.

The FAQ format works well because it gives the agent a clear question-and-answer pattern to follow. Keep answers concise — the agent will use them as a reference and paraphrase naturally during the conversation.

10. Test and Iterate with Real Scenarios

After setting up your agent, use the Test Agent playground to simulate common call scenarios. Test edge cases like callers who ramble, give partial information, or ask unexpected questions. Review call transcripts regularly and refine your instructions based on what you find. Small wording changes in your instructions can make a big difference in how the agent handles calls.