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Introduction

Retell offers two prompt-based approaches for building conversational agents, each suited to different complexity levels and use cases. Understanding when to use each approach is crucial for creating effective AI phone agents.

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Agent Architecture Options

Create Agent Interface
  1. Single Prompt: Design your agent with one comprehensive prompt
  2. Multi-Prompt Tree: Structure your agent with multiple organized prompts

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Single Prompt Agent

A single prompt agent uses one comprehensive prompt to define all agent behaviors, making it the simplest approach to get started.
Single prompt configuration interface showing a unified prompt field

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When to Use Single Prompt

✅ Best for:
  • Simple, straightforward conversations
  • Quick prototypes and testing
  • Agents with 1-3 functions
  • Linear conversation flows

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Limitations at Scale

As complexity increases, single prompt agents may experience:
  1. Behavioral Drift: Agent deviates from instructions in edge cases
  2. Function Calling Issues: Unreliable tool usage with multiple functions
  3. Maintenance Challenges: Large prompts become difficult to debug and update
  4. Context Confusion: Agent struggles to track conversation state
Consider upgrading to multi-prompt when your single prompt exceeds 500 words or uses more than 3 functions.
Multi-prompt agents organize conversations into a structured tree of states, each with its own focused prompt and behavior.
Multi-prompt tree structure showing connected conversation states

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Key Features

Each state in a multi-prompt agent includes:
  • Focused Prompt: Specific instructions for that conversation phase
  • State-Specific Functions: Only relevant tools available in each state
  • Transition Logic: Clear conditions for moving between states
  • Context Preservation: Variables and information flow between states

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Real-World Example: Lead Qualification

Lead qualification template showing two-state structure
This template demonstrates effective state separation: State 1: Lead Qualification
  • Gather customer information
  • Validate requirements
  • No appointment booking functions available
State 2: Appointment Scheduling
  • Only accessible after qualification complete
  • Booking functions enabled
  • Context from qualification available

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Benefits of Multi-Prompt Structure

  1. Predictable Behavior: Each state has a clear, focused purpose
  2. Easier Debugging: Issues isolated to specific states
  3. Better Function Control: Tools available only when appropriate
  4. Scalable Design: Add new states without affecting existing ones
  5. Team Collaboration: Different team members can work on different states
Start with our templates to see multi-prompt best practices in action, then customize for your use case.