Build your first voice agent

The agent builder end-to-end: write the prompt, pick an engine, voice, and languages, attach tools and knowledge, talk to your draft, and deploy it to production.

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.

Start from a template#

Create agent → Start from a template opens a picker of ready-made agents. Everything is editable afterwards.

• Interpreter — a real-time two-way phone interpreter between two languages. Pick your language and the caller's language, a voice that speaks both, and confirm the intro the interpreter says at the start of every call (spoken in the non-English language; in both when neither is English). The agent opens fully configured on Storm at the standard rate; give the number to your team and add the other party with 3-way calling.
• Receptionist — the sample front-desk prompt from the onboarding tour: greets callers, books appointments, answers questions, transfers the rest.
• Appointment scheduler — takes booking, rescheduling and cancellation requests: collects the caller's name, number, and preferred day and time, reads the request back, and tells the caller the office will confirm. There is no calendar integration, so it never claims a booking is confirmed; give it a transfer number for anything it can't handle.
• After-hours message taker — greets, takes the caller's name, callback number and reason, reads them back, and ends the call. Give it an urgent-calls number and it transfers callers who say it's urgent; give it an email and it sends you a summary after each call.
• Call router — a phone-menu replacement. Asks in one sentence what the caller needs, transfers to the matching department (up to three, each with a name and number), and takes a message when nothing fits.
• Lead qualifier — screens calls from your ads: confirms what the caller wants, asks three qualifying questions (what, when, and a rough budget or size), reads the answers back, then transfers to your sales number or promises a callback.
• Info line — answers hours, location, directions, pricing and policy questions from the knowledge you attach, says so when it doesn't know, and never invents facts. After creating it, add your website or documents under Knowledge.
• Phone intake form — walks the caller through a fixed list of fields (name, phone, email, address, reason), confirms each, reads the whole form back, and emails it to you.

The six business templates share one setup step — your business name, a one-line "what you do", and optionally a transfer number and an email for messages — and write a prompt in the prompting guide's shape. Transfers are plain prompt lines ("transfer the call to …"), the email goes through the agent's send-email setting, and the agent is named after your business. Start from scratch in the same menu opens an empty editor instead.

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.

Transfers, keypad presses, hold, email, sounds, and hang-ups are prompted actions. See Built-in tools, and use Transfer calls for cold and screened warm handoffs.

If the call has phases that must happen in order, such as verifying a caller before booking, split the agent into steps instead.

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 pricing reference and agent setting reference.

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 for the full catalog (selected additional languages add 3¢/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 in a few clicks, then let your agent use them during calls.
• API connections — for any other API, create an API connection for the actions your agent needs (paste a cURL command and the AI wizard drafts the tool).
• Knowledge — attach a knowledge base the agent can search mid-call.
• MCP servers — add an MCP server by URL.

See Connections for how the four kinds differ.

Advanced options below the endpoint sections control supervision, connection tone, tool sounds, who speaks first, voicemail, the call-start consent announcement, and silence check-ins. See Every agent setting.

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.

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, get a new ThunderPhone number, import via VoIP, or link a web widget.

Next steps#