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

# How AgentCallback works

> Understand the building blocks of AgentCallback and how a call flows through them.

AgentCallback is a platform for building AI voice agents that make and receive phone calls on your behalf.

## The building blocks

<CardGroup cols={2}>
  <Card title="Voice agents" icon="bot" href="/build-voice-agents/single-prompt">
    The instructions and logic your agent follows during a call — either a Single Prompt or a Pathway.
  </Card>

  <Card title="Phone numbers" icon="phone" href="/phone-numbers/add-your-twilio-credentials">
    The Twilio or SIP numbers your agents use to place and receive calls.
  </Card>

  <Card title="Voices" icon="mic" href="/voices/preview-voices">
    The synthesized voice your agent speaks with, including your own cloned voices.
  </Card>

  <Card title="Campaigns" icon="rocket" href="/deploy/campaigns/overview">
    A contact list, an agent, and a calling schedule bundled together for outbound calling at scale.
  </Card>
</CardGroup>

## How a call happens

1. A phone number receives an inbound call, or a campaign places an outbound call.
2. The assigned agent runs — following a Single Prompt or moving through a Pathway.
3. During the call, the agent can read and update [variables](/build-voice-agents/variables) and [state variables](/build-voice-agents/state-variables), and call [tools](/build-voice-agents/tool-calls) to take actions or fetch data.
4. When the call ends, AgentCallback classifies a [call outcome](/build-voice-agents/call-outcomes) from the transcript.
5. If configured, a [post-call webhook](/build-voice-agents/post-call-webhooks) fires with the call's data.
6. The call is recorded in [Call logs](/monitoring/call-logs), and its outcome rolls up into [campaign](/monitoring/campaign-stats) and [account](/monitoring/overall-stats) stats.

## Two ways to build an agent

* **Single Prompt** — a single set of instructions the agent follows for the whole call. Best for straightforward, open-ended conversations.
* **Pathways** — a visual flow of nodes and transitions. Best for calls that need a fixed step order, branching logic, or escalation paths.

<Tip>
  Start with a Single Prompt if you are not sure which fits. You can move to Pathways later if the conversation needs more structure.
</Tip>

## Next step

[Build your first agent in the Quickstart](/platform/quickstart).