VOICE API

Voice API for AI voice agents

The Vobiz Voice API is a programmable voice API for AI voice agents. Start a call with one REST request, script the flow in VobizXML, stream live audio to your agent over WebSocket, and transfer or record the call while it is in progress.

Explore Voice API

Voice API docs

Talk to an engineer

10min

to first call

Sub-80ms

one-way latency

20ms

audio frames

15M+

calls a day

How it works

From API key to a live call
in three steps

No ticket, no provisioning window. Everything below works from the console or the REST API.

API key123Live call

01Get a number

CountryUS

Search415

Phone number+1 415 555 0100Buy

BASH

1# Place an outbound call: returns a call_uuid2curl -X POST https://api.vobiz.ai/api/v1/Account/$AUTH_ID/Call/ \3-H "X-Auth-ID: $AUTH_ID" -H "X-Auth-Token: $AUTH_TOKEN" \4-H "Content-Type: application/json" \5-d '{"from":"+14155550100","to":"+14155550123",6"answer_url":"https://agent.example.com/answer","answer_method":"POST"}'

VobizXML

XML

1<!-- What your answer_url returns: greet, then stream to your agent -->2<Response>3<Speak>Connecting you now.</Speak>4<Stream bidirectional="true">wss://agent.example.com/ws</Stream>5</Response>

Voice API quickstart

Built for voice AI

Your voice API sets the latency floor
before the model says a word

On Vobiz, media crosses exactly one internal relay,
and streaming and recording fork off the path rather than sitting in it.

One-way latency

<80ms

Speech onset delay

50ms

Signal-to-noise

38.4dB

PESQ MOS

4.2+

Learn more about Vobiz's single-hop architectureKnow more

Vobiz internal measurements.

Live call control

A call control API that works
after the call connects

Call control that ends at setup leaves a failing conversation to run its course. On Vobiz, every live call is addressable by its call_uuid until it hangs up.

Call control reference

Warm transfer to a human

put the caller on hold music while you reach an agent, then connect them with new instructions.

POST /Call/{call_uuid}/withaleg_url

Play, speak and send tones mid-call

inject audio, text-to-speech or DTMF into either side of the call.

/Play//Speak//DTMF/

Record on demand

start and stop recording at any point in the call.

/Record/

Attach a stream to a live call

fork audio to a transcription or QA service after a transfer, without touching the agent's stream.

/Stream/

Conference and supervise

bridge callers into a room, then mute, deafen or remove participants individually.

<Conference>/Conference/{name}/Member/

Answering machine detection

detect voicemail synchronously or asynchronously, then hang up or leave a message.

machine_detection

Real-time audio streaming

Stream live call audio to your
agent over WebSocket

Vobiz

bidirectional WebSocket

Your serverwss://agent.example.com/ws

20 ms frames

Formats your pipeline already uses
— 16-bit linear PCM at 8, 16 or 24 kHz, or μ-law at 8 kHz.
Barge-in flush
— send clearAudio and queued playback stops the moment the caller speaks.
Playback checkpoints
— mark the end of an utterance and get a playedStream event when the caller has actually heard it.
Fork mid-call
— start additional one-way streams over REST for transcription or monitoring, and stop each independently.

Caller audioVobiz → your serverPlaybackyour server → VobizForkone-way, over RESTstartclearAudioplayedStream/Stream/

Vobiz XML

Build an IVR or call flow
in a few lines of XML

When a call connects, Vobiz requests your answer URL and runs the VobizXML you return, top to bottom. Speak, play, gather keypad or speech input, dial out, record, stream, conference or redirect. Classic IVR and AI voice agents run on the same surface.

VobizXML

XML

1<Response>2<Gather numDigits="1" executionTimeout="10" action="https://example.com/menu">3<Speak>Press 1 for billing, or 2 to talk to an agent.</Speak>4</Gather>5<Speak>We didn't get that. Goodbye.</Speak>6<Hangup/>7</Response>

Webhooks and events

Every call event, posted to
your server as it happens

Set an answer URL, ring URL and hangup URL per call. Vobiz posts call context the moment a call arrives, rings, connects and ends, so you can pull customer context or route before the caller hears a word.

EventWhere you set itWhat you get

Call answeredanswer_urlCaller, callee, direction, custom SIP headers. You reply with VobizXML

Ringingring_urlCall status as the far end rings

Call endedhangup_urlDuration, billed duration, hangup cause

Transfer or dial result<Dial action>Dial status and both leg IDs

Voicemail detectedmachine_detection_urlMachine true or false, while the call continues

Your server

POSTring_urlRinging
CallStatus
POSTanswer_urlCall answered
FromToDirectionX-VH-…VobizXML
POSTmachine_detection_urlVoicemail detected
Machine
POST<Dial action>Transfer or dial result
DialStatusDialALegUUIDDialBLegUUID
POSThangup_urlCall ended
DurationBillDurationHangupCause

Observability

Know whether a bad call was
the network or the model

codecPCMU
mos4.5
jitter0ms
packet_loss0%
hangup_sourceCallerhangup_causeNORMAL_CLEARING

Integrations

Connect our voice API
to the agent platform you already run

Self-hosted pipelines take audio straight from the Voice API over WebSocket. Managed agent platforms take the call over SIP. Both run on the same numbers and the same account.

See all integrations

Connecting over SIP?

PlatformHow it connectsSetup guide

Voice API + WebSocket audio streamPipecat integration guide

Dograh·custom STT–LLM–TTS pipelines

Voice API + WebSocket audio streamAudio streaming docs

SIP trunk/integrations/vapi-dashboard/

/integrations/retellai-dashboard/

Agents·

Realtime

SIP trunk/integrations/

SIP trunk/integrations/

Use cases

What developers build
on the Vobiz Voice API

Inbound AI agents

— answer every call with an agent, pull customer context from the webhook before it speaks, and hand off to a human mid-call.

Inbound AI agent guide

Outbound AI calling

— trigger calls from your CRM, scheduler or backend, detect voicemail, and leave a message or retry.

Outbound AI calling campaign

IVR and call routing

— keypad and speech menus in VobizXML, routing to the right queue, agent or AI flow.

IVR example in Python

Click-to-call in your product

— connect your users to their customers from inside your app, with recording and call records on every call.

Browser and in-app calling

Get started

Your first call is
ten minutes away

Get a number, place a call, stream it to your agent.
No ticket, no sales call, no commitment.

Start free

Voice API docs

Book a demo

FAQ

Voice API questions

: A voice API lets your software place, answer and control phone calls over HTTP instead of through a phone system. You send a request to start a call, and the platform asks your server what to do as the call progresses: speak, gather input, transfer, record or stream the audio somewhere.
: A programmable voice API for AI voice agents. Start a call with one REST request, script the flow in VobizXML, stream live audio to your agent over a bidirectional WebSocket, and transfer, record or conference the call while it is in progress, all addressed by its call_uuid.
: Buy a number by API, point it at your answer URL, and return a <Stream> verb when a call arrives. Vobiz opens a WebSocket to your agent and sends the caller's audio in 20 ms frames; your agent sends its audio back over the same socket. Managed agent platforms such as Vapi or Retell connect over a SIP trunk instead.
: Send a POST to /Call/ with the from number, the to number and an answer_url. The response carries the new call's call_uuid, and when the call connects Vobiz requests your answer_url for the VobizXML to run.
: 16-bit linear PCM at 8, 16 or 24 kHz, or μ-law at 8 kHz, in 20 ms frames. The stream is bidirectional, supports clearAudio to flush queued playback on barge-in, and reports playedStream when the caller has actually heard a marked utterance.
: Yes. VobizXML covers keypad and speech menus with <Gather>, plus <Speak>, <Play>, <Dial>, <Record>, <Conference>, <Redirect> and the rest, so a classic IVR and an AI agent run on the same surface, and one can hand off to the other.
: Send POST /Call/{call_uuid}/ with an aleg_url. Vobiz fetches new VobizXML from that URL for the caller, typically hold music, then a <Dial> to your agent, and the call moves without dropping.
: Yes. Set machine_detection on the call, synchronously or asynchronously, and Vobiz posts the result to your machine_detection_url while the call continues, so you can hang up or leave a message.
: No provider can promise that: spam labels are applied by the receiving carriers and apps. What helps is calling from numbers registered for the purpose, keeping volumes and answer rates healthy, and meeting the rules of each market you call into, such as caller-ID authentication in the US.
: Yes. Record a whole call with <Record>, or start and stop recording at any point with the /Record/ endpoint on a live call. Check the consent rules for recording in the places you call.
: Every call detail record carries 43 fields, including MOS, jitter, packet loss, the negotiated codec, and which side hung up and why. If those are clean, the audio reached your agent intact and the problem is upstream of the network.
: About ten minutes: get a number, place a call, stream it to your agent. There is no ticket and no provisioning window; everything works from the console or the REST API.
: You do not need one. The Voice API is plain REST plus VobizXML, so any HTTP client works, as the cURL, Python and Node.js samples on this page show. See the docs for the client libraries currently available.
: A conversational turn has roughly 500 ms before a pause feels unnatural, and speech-to-text, the model, text-to-speech and the network all spend from it. Vobiz keeps the network's share small: under 80 ms one-way, with media crossing exactly one internal relay.