Voice AI agent API with MCP, built in Japan

Conversational AIfor Developers

On the phone, the web or in your app, an AI agent talks with your customers in Japanese and other languages and takes care of inquiries and bookings. Configure its role (say, a dental clinic receptionist), the fields to collect and the FAQ, and it holds the conversation exactly that way, then returns the result through an API and webhooks. Your phone numbers and screens stay yours. You plug in just the conversation, through an API.

Contact us
avacast Avatar conversations Booking Calendar CRM Avatar desk Voice app Cloud phone

Features

From picking up the call to handing back the result, voicast handles the conversation.

  • Talks in the role you set, in many languages

    Set the role, tone and greeting (for example, a calm dental clinic receptionist), and the AI follows them, using speech recognition, an LLM and speech synthesis. It talks in Japanese, English and other languages.

  • Collects the details you need

    Name, callback number and reason for the call, plus any custom fields you define.

  • Reads it back to confirm

    It reads back what it heard. If something is wrong, the caller can correct it on the spot.

  • Hands off to your staff

    When a condition you set is met (for example, the caller asks for a person), the AI decides to hand off and ends the conversation. The call returns to your SaaS, which transfers it to a staff phone.

  • Answers common questions

    Give it answers such as your opening hours and it replies right away when asked.

  • Results over the API

    Fetch the outcome, reason, collected fields, duration and cost using your own call ID.

  • A conversation setup per use case

    Set the role and tone, greeting, fields to collect, handoff conditions, closing line, FAQ, and hints for the industry and its vocabulary. Every change is versioned.

  • Separate setups per customer

    Give each of your customers (the business actually taking the calls) its own connection key and conversation setup.

  • Dashboard

    Manage organizations, projects, live and test environments, roles (owner / admin / developer / viewer) and API keys. Sign in with a passkey (SealGate) or an email link.

What you can build

Combine voicast with the systems and services you already use, and let AI handle the conversations on your phones and in your apps.

Call center system×=

AI handles first contact and hands off only when needed

The AI picks up calls coming into your call center system (cloud phone or CTI) and finds out what the caller needs. It answers common questions itself and transfers to an agent only when a person is needed.

These are example combinations. You connect each service on your side, using the API and webhooks.

How it works

voicast slots into one step of your existing call flow.

  1. Stream the call audio to voicast

    Add <Connect><Stream> to your TwiML. The tenant and secret are the connection key for each of your customers.

    TwiML (your SaaS)
    <Response>  <Connect action="https://your-saas.example/voice/next">    <Stream url="wss://voice.voicast.jp/ws">      <Parameter name="tenant" value="TENANT_ID" />      <Parameter name="secret" value="CONNECTION_SECRET" />    </Stream>  </Connect></Response>

  2. voicast holds the conversation

    It collects and confirms the details, decides whether to hand off, then closes the stream. The call returns to your flow through the Connect action (for example, ringing your staff).

    1. Listen
    2. Read back to confirm
    3. Decide on handoff
    4. Close the stream
    5. Back to your action

  3. Fetch the result by call ID

    Once the stream closes, fetch the result with the Twilio CallSid.

    Fetch the result
    curl https://api.voicast.jp/v1/calls/by-provider/CA0123456789abcdef \  -H "Authorization: Bearer $VOICAST_API_KEY"

    What you get back: outcome, reason, collected fields, duration and cost

    • completedAll details collected
    • answeredResolved by an FAQ answer
    • handoffHand off to staff
    • hangupCaller hung up
    • errorError

Read the docs for the API, webhooks, MCP and the SDK

Use cases

Change the conversation setup and it fits the calls of a different industry.

  • Dental clinic

    Bookings and changes

    Connected to the booking system, it checks open slots and books or changes appointments during the call. It also answers common questions such as opening hours.

  • Real estate

    Viewing requests

    Collects the property and preferred time, then sets up a callback from an agent.

  • Restaurant

    Table bookings

    Takes the date, time, party size, name and phone number. Connected to a calendar, it can check availability and book on the spot.

  • B2B support

    First-line support calls

    Collects the company name and the issue. When a condition is met, the AI decides to hand off and your SaaS transfers the call to a staff phone.

  • After hours

    After-hours calls

    Answers calls outside business hours, takes down the request and a callback number, so staff can call back the next business day.

  • Auto repair

    Service booking calls

    Besides name and callback number, it collects the car model and preferred date.

These are example setups, not customer case studies.

Built to be dependable

Safeguards against missed calls are built in from the start.

  • Phone number checks

    Checks that it is a 10–11 digit Japanese number starting with 0, and asks again if not.

  • Read-back and corrections

    Reads back what it heard and updates it when the caller corrects it.

  • Stops when interrupted

    When the caller starts talking, voicast stops speaking and listens (barge-in).

  • Handles silence

    If the caller goes quiet, the conversation does not just stall.

  • Calls keep going even if voicast does not

    If voicast is down or the connection key is wrong, the stream closes immediately and the call moves on to the next step in your flow.

  • Live calls keep their setup

    Updating the conversation setup never changes a call in progress; it keeps the version it started with.

Why no phone numbers

voicast owns neither phone numbers nor lines. It is the component that handles the conversation, split the same way as the voice AI APIs overseas.

Your SaaS owns

  • Contracts and support for your customers
  • Phone numbers and lines (Twilio and others)
  • Transfers, ring groups and the rest of the flow

voicast owns

  • The conversation during the call
  • Collecting and confirming details
  • Recording results and the API

  • Your customers stay yours

    Contracts and support for the businesses taking the calls remain with your SaaS, as they are today.

  • Keep your numbers and lines

    Numbers and phone settings stay where they are, such as your SaaS’s Twilio account.

  • Keep your transfer flow

    Ring groups and whatever happens after voicast are decided on your side.

  • Combine it with other components

    Pair it on your side with avacast, Shannon’s headless platform for avatar conversations, and an avatar talks with your customers in voice and video.

Pricing

Pay as you go

Per minute of calls

Contact us for pricing.

  • You pay for the call time you use.
  • The cost of each call is also returned by the results API.
Contact us

FAQ

What does the AI talk about?
It follows the conversation setup for each use case: its role and tone (for example, a calm dental clinic receptionist), the opening greeting, the details to collect, answers to common questions, and the conditions for handing off to staff. You set these in the dashboard or through the API.
Which languages can it talk in?
Japanese, English and other languages.
Where are call audio and conversations processed?
Speech recognition, generative AI and speech synthesis combine APIs from inside and outside Japan, so call audio and conversation content may be processed outside Japan.
Does voicast provide phone numbers?
No. You use the numbers and lines you already have (for example, your SaaS’s Twilio account). voicast receives the call audio over a WebSocket and holds the conversation.
What happens to calls if voicast is down?
If it cannot be reached or the connection key is wrong, the stream closes immediately and the call moves on to the next step in your flow (for example, ringing your staff).
Can I change which details are collected?
Yes. Besides name, callback number and reason for the call, you can add your own fields to the conversation setup. Fields can be text or phone numbers.
What happens to live calls when I change the setup?
Setups are versioned. A call in progress keeps the version it started with, and the next call uses the new one.
How do I receive the result?
After the stream closes, call GET /v1/calls/by-provider/{CallSid} with the Twilio CallSid. You get the outcome (completed / answered / handoff / hangup / error), reason, collected fields, duration and cost.
How is pricing calculated?
Pay as you go, per minute of calls. Contact us for details.

Let’s talk

Get in touch and we will walk you through connecting voicast and setting it up.

Contact us