Vapi Integration

KugelAudio has a built-in Vapi custom TTS endpoint — no proxy server needed. Just point your Vapi assistant at our API and you’re done.

Setup

1. Get your KugelAudio API key and a voice ID

API key — open the KugelAudio dashboard, then go to Settings → API Keys.
Voice ID — open the KugelAudio dashboard, go to Voices, pick a voice, and copy its numeric ID.

2. Configure your Vapi assistant

Pick whichever flow you prefer — the dashboard is faster for one-offs, the API is better for scripted setup.

Vapi Dashboard
Vapi API

Open the assistant

In the Vapi dashboard, open the assistant you want to use.

Go to Voice → Provider

Click Voice, then Provider.

Pick Custom Provider

Scroll down in the provider list and select Custom Provider.

Paste the URL

https://api.kugelaudio.com/vapi/synthesize?voice_id=YOUR_VOICE_ID&api_key=YOUR_KUGELAUDIO_API_KEY

Save

Save the assistant. The voice is now powered by KugelAudio.

The “Voice ID” field inside Vapi’s UI has no effect when using a custom provider — the voice_id query param in the URL is what selects the voice.

Use PATCH /assistant/{id} to update an existing assistant, or include the voice field when creating a new one with POST /assistant:

{
  "voice": {
    "provider": "custom-voice",
    "server": {
      "url": "https://api.kugelaudio.com/vapi/synthesize?voice_id=YOUR_VOICE_ID&api_key=YOUR_KUGELAUDIO_API_KEY",
      "timeoutSeconds": 30
    }
  }
}

voice_id — the numeric voice ID from Step 1.
api_key — your KugelAudio API key. KugelAudio authenticates it on every request.

As an alternative, you can pass the API key in Vapi’s server.secret field instead of the URL. Vapi will send it as the x-vapi-secret header on every request and KugelAudio will authenticate it the same way.

That’s it. No code, no extra server, no proxy.

To select the model explicitly, add &model_id=kugel-3 to the URL.

How it works

Vapi sends one POST per phrase to /vapi/synthesize:

{
  "message": {
    "type": "voice-request",
    "text": "Hello, how can I help you today?",
    "sampleRate": 24000
  }
}

KugelAudio streams back raw PCM16 at the requested sample rate — exactly what Vapi expects. message.sampleRate must be one of 8000, 16000, 22050, 24000, or 44100; unsupported rates are rejected with 400.

Audio format

Parameter	Value
Format	Raw PCM (no WAV/container header)
Bit depth	16-bit signed, little-endian
Channels	1 (mono)
Sample rate	Matches `message.sampleRate` from Vapi’s request

Get started

Build a voice agent

Generate audio

Voices

Deploy

SDK Reference

API Reference

Setup

1. Get your KugelAudio API key and a voice ID

2. Configure your Vapi assistant

How it works

Audio format

​Setup

​1. Get your KugelAudio API key and a voice ID

​2. Configure your Vapi assistant

​How it works

​Audio format

Setup

1. Get your KugelAudio API key and a voice ID

2. Configure your Vapi assistant

How it works

Audio format