
The first sentence has a job: make the caller stay on the line long enough for the second sentence to matter.
Before You Begin
Write down the agent’s single objective, required facts, prohibited behavior, escalation rules, and a clear definition of success. Collect approved wording for sensitive or regulated statements.Prompt Fields And Meaning
Write each field for a different purpose.Variable Syntax Validation
The agent builder validates dynamic variable placeholders before saving, testing, or publishing prompt-related text. Use simple double-brace syntax such as{{first_name}}. Prompt text, welcome messages, and voicemail messages must be valid Handlebars template text.
The validation message points to the first affected line and can report additional errors after that. Fix malformed variables before changing the prompt content itself.
System prompt text is static. Put dynamic caller data in the main prompt, welcome message, voicemail message, default variables, batch CSV, workflow lead data, or API launch payload instead.
Conversation Start Modes
- User starts
- Agent defined
- Agent dynamic
The caller speaks first. Good for inbound calls where the caller has a reason to call.
Write Prompt Instructions That Survive Real Calls
1
Name the caller goal
Tell the agent the single most important outcome.
2
Define what not to do
Add boundaries for speculation, pricing, escalation, or unsupported requests.
3
Use examples
Include phrasing for short answers, objections, wrong number, busy caller, and language switch.
4
Connect tools to intent
Tell the agent when to use functions, not just that functions exist.
5
Make the ending explicit
Tell the agent when to end, transfer, schedule, or summarize.
Prompt Review Questions
Does the agent know success?
Does the agent know success?
If success is vague, post-call fields and summaries will be vague too.
Are variables wrapped correctly?
Are variables wrapped correctly?
Use placeholders such as
{{first_name}} and define defaults where needed.Does the welcome message match the route?
Does the welcome message match the route?
Inbound and outbound openings usually need different wording.
Can the prompt be shorter?
Can the prompt be shorter?
Long prompts are sometimes necessary, but repeated rules and unclear sections make behavior harder to debug.
Verify The Prompt And Welcome Message
Test the normal path, an interruption, silence, an out-of-scope question, a correction, and a request for a human. Confirm the agent stays within scope and the transcript reflects the intended behavior.Related Reading
Dynamic Variables
Add caller-specific values.
Single Prompt Agents
Use one instruction set.
Testing Agents
Test the first turn and edge cases.
Agent Prompts Video
Watch how to write focused agent instructions.
Welcome And System Prompt Video
Watch how the opening and core instructions work together.