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

# Introduction

> Build voice AI agents that make and receive phone calls

Nixflex is a real-time voice AI platform. You connect your Twilio number, give the agent a prompt, and your phone agent is live. Inbound and outbound calls, SMS, transfers, post-call analysis, batch campaigns — all behind one API.

Built for developers embedding voice agents into SaaS apps.

## Why Nixflex

<Columns cols={2}>
  <Card title="Sub-second response" icon="bolt">
    First audio in \~500ms. speech engine for STT, the AI for reasoning, the voice engine for voice.
  </Card>

  <Card title="Bring your own Twilio" icon="phone">
    Multi-tenant from day one. Each customer connects their own Twilio account — you keep full control of phone numbers and billing.
  </Card>

  <Card title="Tag-based actions" icon="tag">
    The agent triggers transfers, SMS, and call endings through prompt tags. No webhook orchestration needed for built-in actions.
  </Card>

  <Card title="History-aware calls" icon="clock-rotate-left">
    Outbound calls automatically pull past call summaries for the recipient and inject them into the agent's prompt. Your agent remembers customers across calls.
  </Card>
</Columns>

## Get started

<CardGroup cols={2}>
  <Card title="Quickstart" icon="play" href="/quickstart">
    Make your first call in under five minutes.
  </Card>

  <Card title="Authentication" icon="key" href="/authentication">
    Generate API keys and authenticate requests.
  </Card>

  <Card title="Create an agent" icon="user-plus" href="/concepts/agents">
    Configure prompts, voice, language, and actions.
  </Card>

  <Card title="API reference" icon="code" href="/api-reference/introduction">
    Every endpoint with parameters, examples, and error codes.
  </Card>
</CardGroup>

## How it works

A call moves through the engine like this:

1. **Caller dials your Twilio number** (or you trigger an outbound call via API).
2. **Twilio streams audio** to Nixflex over WebSocket.
3. **Speech-to-text** converts what the caller says into text in real time.
4. **The agent reasons** over the conversation and decides what to say or do next.
5. **Text-to-speech** turns the reply into natural voice and streams it back to the caller.
6. **After the call ends**, Nixflex runs post-call analysis (summary, sentiment, custom data extraction) and fires your webhook.

You configure the agent's behaviour with a system prompt and a handful of settings. Everything else — audio handling, interruption detection, language matching, voicemail filtering — is handled by the engine.

## Built-in capabilities

<Columns cols={2}>
  <Card title="Inbound + outbound calls" icon="phone-arrow-up-right" />

  <Card title="Cold and warm transfers" icon="shuffle" />

  <Card title="Mid-call and post-call SMS" icon="message" />

  <Card title="Voicemail detection (AMD + the speech engine)" icon="voicemail" />

  <Card title="Batch voice + SMS campaigns" icon="users" />

  <Card title="Auto language detection (15+ languages)" icon="globe" />

  <Card title="Post-call summary, sentiment, data extraction" icon="chart-line" />

  <Card title="Custom functions (tools the agent can call mid-call)" icon="wrench" />
</Columns>

## Pricing

Pay-as-you-go from **\$0.08 per minute** of voice. SMS billed per message at your Twilio rate.

See [pricing details](/reference/pricing) for plans and volume discounts.

## Need help?

Email [support@nixflex.com](mailto:support@nixflex.com) or check the [error reference](/reference/errors) for common issues.