Introduction
Function calling transforms your AI agent from a conversational interface into an action-oriented assistant. By connecting your agent to functions, you enable it to interact with external systems, manage call flows, and perform real-world tasks.Common Use Cases
Function calling enables your agent to:Call Management
- Transfer calls: Route to human agents or other departments
- End calls: Gracefully terminate conversations
- Send DTMF tones: Navigate phone menus
Business Operations
- Book appointments: Integrate with scheduling systems
- Check availability: Query calendars or inventory
- Process orders: Create, modify, or cancel orders
Data Integration
- Retrieve information: Pull data from CRMs, databases, or APIs
- Update records: Modify customer information or case details
- Send notifications: Trigger emails, SMS, or push notifications
How Function Calling Works
The Process
- Agent Decision: Based on the conversation context, the LLM determines when a function is needed
- Parameter Extraction: The agent extracts required information from the conversation
- Function Execution: Retell calls your function with the extracted parameters
- Response Handling: The function result is processed and incorporated into the conversation
Technical Overview
Function calling uses structured JSON to communicate between the LLM and your systems:Additional Resources
- OpenAI’s Function Calling Guide: Technical deep dive
- Function Calling Tutorial: Step-by-step implementation guide
Configuring Tool Calls
Dashboard Configuration
Access and manage tools in the agent detail page under the “Functions” section.
Available Function Types
1. Pre-built Functions
Retell provides ready-to-use functions for common scenarios:| Function | Purpose | Common Use Cases |
|---|---|---|
| End Call | Terminate conversation gracefully | After completing tasks, when caller requests |
| Transfer Call | Route to human agents | Escalation, department routing |
| Press Digits | Send DTMF tones | Navigate IVR systems, enter codes |
| Check Availability | Query available time slots | Appointment scheduling |
| Book Calendar | Create calendar events | Confirm appointments, meetings |
| Send SMS | Send text messages | Confirmations, follow-ups |
2. Custom Functions
Create your own functions to:- Integrate with your APIs: Connect to CRM, ERP, or custom systems
- Execute business logic: Validate data, calculate prices, check inventory
- Trigger workflows: Start processes in other systems
Custom Function Features
- Flexible parameters: Define any input structure
- Async execution: Run in background without blocking conversation
- Error handling: Graceful fallbacks for failures
- Response control: Customize what the agent says during/after execution
Video Tutorial
Additional Resources
- Community Templates: Real-world function examples
- API Reference: Technical documentation
- Best Practices: Writing effective function prompts