> ## Documentation Index
> Fetch the complete documentation index at: https://docs.turncall.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Introduction

> Voice AI infrastructure you can self-host

TurnCall lets developers deploy AI voice agents over phone calls, WebRTC browser calls, WhatsApp, and SMS — with configurable providers, tool calling, call transfers, voicemail detection, and bidirectional server events.

Define an agent via API, bind it to a phone number, and callers talk to your AI.

## Features

<CardGroup cols={2}>
  <Card title="Twilio PSTN Calls" icon="phone">
    Inbound and outbound phone calls via Twilio Voice + Media Streams.
  </Card>

  <Card title="WebRTC Browser Calls" icon="globe">
    Talk to agents directly from the browser with peer-to-peer audio.
  </Card>

  <Card title="Video Avatar" icon="user-circle">
    Optional lip-synced video avatar (HeyGen or Tavus) on WebRTC cascade calls.
  </Card>

  <Card title="WhatsApp Business" icon="whatsapp" color="#25D366">
    Voice calls and text messages via WhatsApp Cloud API.
  </Card>

  <Card title="SMS / Chat" icon="message">
    Text-based conversations with agents via Twilio SMS or the Chat API.
  </Card>

  <Card title="Multi-Provider" icon="shuffle">
    Mix and match STT, LLM, and TTS providers per agent — Deepgram, OpenAI, Anthropic, ElevenLabs, Cartesia, Ollama.
  </Card>

  <Card title="Speech-to-Speech" icon="bolt">
    Ultra-low latency (\~300ms) via OpenAI Realtime or Gemini Live.
  </Card>

  <Card title="Tool Calling" icon="wrench">
    Built-in tools (transfer, handoff, DTMF) + webhook tools + MCP servers.
  </Card>

  <Card title="Knowledge Base (RAG)" icon="book">
    Upload documents with three retrieval modes: prompt, auto, and tool.
  </Card>

  <Card title="Agent Versioning" icon="code-branch">
    Publish immutable versions, auto-promote phone numbers, rollback instantly.
  </Card>

  <Card title="A/B Testing" icon="flask">
    Weighted traffic routing on phone numbers, deterministic by caller.
  </Card>

  <Card title="Post-Call Analysis" icon="chart-bar">
    Automatic summary, sentiment, success evaluation, and structured extraction.
  </Card>

  <Card title="Server Events" icon="arrows-left-right">
    Bidirectional hooks — call-init, function-call, call-end, transcript updates.
  </Card>
</CardGroup>

## How It Works

A caller connects over any transport; TurnCall runs a per-call Pipecat pipeline in one of two modes and streams audio back.

```mermaid theme={null}
flowchart LR
    Phone["📞 Phone"] --> TC
    Browser["🌐 Browser"] --> TC
    WhatsApp["💬 WhatsApp"] --> TC

    TC["TurnCall<br/>webhook / connect"] --> MODE{"pipeline_mode"}
    MODE -->|cascade| C["STT → VAD + SmartTurn → LLM → TTS<br/>~800ms"]
    MODE -->|s2s| S["OpenAI Realtime / Gemini Live<br/>~300ms"]
    C --> OUT["🔊 Audio back"]
    S --> OUT
```

See [Architecture](/architecture) for the full pipeline, call flows, and data model.

## Tech Stack

| Component      | Technology                                                              |
| -------------- | ----------------------------------------------------------------------- |
| Framework      | FastAPI + Uvicorn                                                       |
| Voice Pipeline | Pipecat 1.4                                                             |
| Database       | PostgreSQL + SQLAlchemy async + Alembic                                 |
| Cache          | Redis                                                                   |
| Telephony      | Twilio Voice + Media Streams                                            |
| Browser        | WebRTC (SmallWebRTCTransport)                                           |
| Video Avatar   | HeyGen / Tavus (Pipecat avatar services)                                |
| STT            | Deepgram / OpenAI / ElevenLabs / Cartesia                               |
| LLM            | OpenAI / Anthropic Claude / Ollama / OpenRouter / Any OpenAI-compatible |
| TTS            | Deepgram / OpenAI / ElevenLabs / Cartesia                               |
| S2S            | OpenAI Realtime / Gemini Live                                           |
| Knowledge Base | pgvector + OpenAI embeddings                                            |
| VAD            | Silero                                                                  |
| Turn Detection | Smart Turn V3 (local ONNX)                                              |