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

# Build your first voice agent

> The agent builder end-to-end: prompt, engine, voice and languages, tools and knowledge, talk, and deploy.

Everything about an agent lives in the builder at **Voice Agents**
(`/dashboard/agents`) — create one and you land in it. This guide
walks the same path as the in-app "Build an agent" tour.

<Tip>
  First time here? The [dashboard quickstart](/quickstart-dashboard)
  wraps this page plus billing, numbers, and simulations into the
  five-step setup wizard.
</Tip>

## 1. Write the prompt

The prompt is the script for your voice agent. Describe — in any
language — who the agent is and how it should handle the call: its
persona, what it knows, what it should and shouldn't do.

Call actions are prompted too. Transfers, keypad presses, and hang-ups
are plain prompt lines like *"If the caller asks for a human, transfer
the call to +1 555…"* — no separate configuration.

<Tip>
  Specific beats general. "Confirm the order number back to the caller
  before making changes" outperforms "be careful with orders."
</Tip>

## 2. Pick an engine

On the **Config** tab, the engine picker trades off cost and
performance across three tiers — **Spark** is optimized for cost,
**Bolt** for speed, **Storm** for intelligence on complex prompts.
Each card shows its per-minute price. Switch anytime; see the
[full tier comparison](/api-reference/agents#product-tiers-at-a-glance).

## 3. Choose a voice and languages

Pick a voice and play its sample right in the builder. Set the
**primary language** the call starts in, plus any **additional
languages** — the agent switches automatically when a caller uses one.
The voice list filters to voices that support every language you've
selected. See [Supported languages](/guides/supported-languages) for
the full catalog (premium languages add 2¢/min).

## 4. Attach tools and knowledge

Four sections on the Config tab give the agent capabilities:

* **Connected apps** — the easiest path:
  [connect Slack, HubSpot, Google & more](/guides/connect-apps) in a
  few clicks, then let your agent use them during calls.
* **API connections** — for any other API,
  [create an API connection](/guides/api-connections) for the actions
  your agent needs (paste a cURL command and the AI wizard drafts the
  tool).
* **Knowledge** — attach a
  [knowledge base](/guides/knowledge-base) the agent can search
  mid-call.
* **MCP servers** — [add an MCP server](/guides/mcp-servers) by URL.

See [Connections](/guides/concepts#connections) for how the four kinds
differ.

## 5. Watch your all-in rate

The builder shows your **all-in per-minute rate** — engine plus
surcharges — and updates it live as you change settings. No surprises
on the bill.

## 6. Talk to it

Click **Talk** and say hello — your agent answers right in the browser
(it'll ask for mic access). This is the fastest iteration loop:
tweak the prompt, talk, repeat. When you want a caller on the other
end instead of yourself, [run a simulation](/guides/simulate-a-call).

## 7. Deploy

Every edit **autosaves to your draft** — watch for "Saved" in the top
bar. Draft changes aren't live until you click **Deploy**.

Every deploy is snapshotted in the **History** tab: inspect what
changed between versions and restore any previous one. That makes
deploys safe to do often — you can always roll back.

## 8. Connect it to the world

The Config tab's **Phone numbers** and **Web widgets** sections attach
endpoints without leaving the builder — attach an existing number,
provision a new demo number, import via VoIP, or link a web widget.

***

## Next steps

<CardGroup cols={2}>
  <Card title="Get a phone number" icon="phone" href="/guides/get-a-phone-number">
    Demo number in seconds, or bring your own via VoIP.
  </Card>

  <Card title="Simulate a call" icon="flask" href="/guides/simulate-a-call">
    An AI caller has a real conversation with your agent.
  </Card>

  <Card title="Review the calls" icon="headset" href="/guides/review-calls">
    Transcripts, recordings, live listen-in, and whisper.
  </Card>

  <Card title="Agents API reference" icon="code" href="/api-reference/agents">
    Create and manage agents programmatically.
  </Card>
</CardGroup>