Retell AI Prompt Engineering: Write Prompts That Convert

The 'new hire' method

The best way to write a voice-agent prompt is to imagine training a new front-desk hire on day one. Write down exactly what you'd tell them — and that becomes your prompt.

• Who is calling and what they usually want
• The answers you give 90% of the time
• When to escalate or hand off to a human
• The tone and personality you want

How to structure the prompt

A good prompt has clear parts, not one wall of text.

• Role & goal — who the agent is and its job
• Knowledge — the facts it needs (or point it to a knowledge base)
• Rules — what it must and must not do
• Style — tone, length, how it speaks
• Handoff — exactly when to transfer to a human

Make it sound natural, not scripted

Voice is different from chat — people interrupt, ramble and change their minds.

• Keep responses short and conversational
• Allow interruptions and handle them gracefully
• Confirm key details (times, names, numbers)
• Avoid robotic, repeated phrasing

Common prompt mistakes

Most agent failures trace back to the prompt.

• Too long, vague or contradictory instructions
• No clear handoff rules, so callers get stuck
• Trying to handle every edge case in the prompt (use functions/RAG instead)
• No testing on real, messy conversations

Official resources

For primary documentation, see: Make.com · n8n · Zapier.