When your data lives in your own system (orders, appointments, accounts, tickets), give the AI voice agent a custom tool to reach it during the call. You describe the tool (name, what it does, which details it needs) and point it at your API. When a caller asks "where's my order?" or picks a slot, the agent calls your endpoint and answers from the result. A multi-branch hospital we work with books appointments this way, through tools for locations, doctors, free slots and booking.
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What a tool definition includes
| Part | Example |
|---|---|
| Name | get_order_status |
| Description | "Look up the status of an order by order ID or phone number" |
| Parameters | order_id (string), phone (string) |
| Endpoint | Your HTTPS API URL, with authentication |
The description matters: it tells the agent when to use the tool.
Common tools
- Order lookup: status, delivery date, tracking.
- Slot availability and booking: doctors, technicians, site visits.
- Account lookup: balance due, due date, plan.
- Ticket creation: log a complaint with the caller's words.
- Eligibility check: pincode serviceability, loan pre-check.
Example: appointment booking tools
A hospital's agent uses a chain of tools:
- Find location → 2. Find specialty and doctor → 3. Get free slots → 4. Identify patient →
- Book / reschedule / cancel.
See how a hospital uses AI for follow-up calls.
Rules for reliable tools
- Speak before every tool call to avoid dead air (guide).
- Keep APIs fast: a few hundred milliseconds is ideal on a phone call.
- Return short, clear results: the agent reads them aloud.
- Handle "not found": ask again once, then transfer or take a message.
- Check time zones on anything with dates and times.
- Never expose sensitive data the caller hasn't been verified for.
Built-in first
Before building a custom tool, check the built-in integrations: HubSpot, Salesforce, Zoho CRM, GoHighLevel, Google Calendar, Cal.com, Google Sheets, Shopify and more. Custom tools cover the rest. For the reverse direction (your system starting calls), see trigger calls from your app via API.
Try it
Create a free account, add one lookup tool pointing at a test endpoint, and ask your agent about an order. Need help designing tools for your system? Talk to us.