Patter: Dynamic Variables

Per-call prompt personalization with {variable} placeholder substitution in system prompts and first messages.

Part of the Patter Voice AI SDK.

Prerequisites

• Twilio account with a phone number
• OpenAI API key with Realtime access

Quick Start

Python

cd python
cp ../.env.example .env   # fill in your keys
pip install -r requirements.txt
python main.py

TypeScript

cd typescript
cp ../.env.example .env   # fill in your keys
npm install
npx tsx main.ts

Environment Variables

Variable	Required	Description
OPENAI_API_KEY	Yes	OpenAI API key with Realtime access
TWILIO_ACCOUNT_SID	Yes	Twilio account SID
TWILIO_AUTH_TOKEN	Yes	Twilio auth token
TWILIO_PHONE_NUMBER	Yes	Your Twilio phone number (E.164)
WEBHOOK_URL	No	Public URL for webhooks (auto-tunneled if omitted)

What This Demonstrates

• variables in agent() — define default placeholder values when creating an agent
• {placeholder} syntax — use {customer_name}, {account_number}, etc. in system prompts and first messages
• on_call_start returning variable overrides — dynamically swap variables per caller at runtime
• Per-caller personalization — look up caller info from a database and inject it into the conversation

How It Works

1. Define an agent with {variable} placeholders in the system prompt and first message
2. Provide default values via the variables parameter
3. When a call comes in, on_call_start looks up the caller in a database
4. If found, return {"variables": {...}} to override defaults for that specific call
5. Patter substitutes all placeholders before the conversation begins

Next Steps

• Inbound Agent — minimal inbound voice agent
• Custom LLM — bring your own LLM
• Production Setup — full production configuration
• Full documentation
• All templates

License

MIT