The difference between an agent that frustrates callers and one that delights them usually comes down to a few paragraphs of instructions. Here's how to write them well.
Start with a warm first message
The first message sets the tone. Keep it short, identify the business, and invite the caller to speak. Avoid long menus — the whole point of a voice agent is that people can just say what they need.
Give the system prompt a clear role
Tell the agent who it is, what it can help with, and what's out of scope. Be explicit about tone (friendly, concise, professional) and about when to transfer to a human or end the call.
- Define the agent's job in one or two sentences
- List the tasks it can complete and the tools it can use
- Spell out how to handle unknowns — never invent facts
- Describe when to hand off, take a message, or say goodbye
Good prompts don't script every sentence — they set boundaries and let the agent sound natural inside them.
Plan for the messy parts
Real calls have crosstalk, silence, and unexpected questions. Instruct your agent to ask clarifying questions, confirm important details, and gracefully fall back to a human when it's unsure. Then test with real calls and refine using the transcript review tools.