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Voice Documentation


Nexmo is now called Vonage, but there are still references to Nexmo in our URLs, code snippets and message templates.

Vonage's Voice API allows you to create and manage high-quality voice operation applications on the cloud, such as IVR, WebRTC and PSTN calling. Voice is a HTTP-based RESTful API. It is accessed over HTTPS combined with OAuth2.0 for extra security. Request and response bodies follow the JSON format to make the exchange of information fast, easy and reliable.

API specification

Test the API on SwaggerHub

Base URL


Conceptual model

Nexmo Voice conceptual model


Conversation, leg, conference

Communication can be 1-to-1 or 1-to-n from or to the Vonage platform. While 1-to-1 calls are known as a leg, 1-to-n calls are known as a conversation. Each call connected to a conversation is its own leg.


A Nexmo Call Control Object (NCCO) is a JSON array that you use to control the flow of a Voice API call. For your NCCO to execute correctly, the JSON objects must be valid.

The Call event model is asynchronous. A static or dynamically created NCCO script provides the business logic for your Call. When a Call is placed to your number, Vonage (formerly Nexmo) makes a synchronous request to the webhook endpoint you set as the answer_url for your number and retrieves the NCCO object that controls the Call.

Extended information regarding NCCOs can be found in our NCCO reference page.


Method to augment or alter the behavior of your application via user-defined HTTP callbacks. In your case webhook defines the behavior of your application.


Dual Tone Multi Frequency (DTMF), is a form of signaling used by phone systems to transmit the digits 0-9 and the * and # characters.

Text to speech

Vonage uses text to speech engines to allow you to play machine generated speech in your calls. This feature can be added via NCCOs with the use of talk action or by making a put request on an in-progress call. There are 23 languages available with different styles and genders.


Vonage's Voice API offers the ability to record call audio in several ways:

SIP Trunk

To use Session Initiation Protocol (SIP), see the SIP documentation page.

API workflow

Documentation page Vonage Voice API workflow


  • Scales with existing web solutions.
  • Easy to configure.
  • Records and stores any call.
  • Conference calls.
  • Text to speech messages in 23 languages.

Getting started

Make sure you've read What's in it for you for more info on how to register and start testing APIs.


The API follows the KPN Store API Authentication Standard to secure the API. It includes the use of OAuth 2.0 client_id and client_secret to receive an access token.

Go to the Authentication tab on top of this page to find out how to:

  • Authenticate to an API using cURL.
  • Authenticate to an API on Swaggerhub.
  • Import Open API Specifications (OAS), also called Swagger files into Postman.

How to...

The API is divided into 2 groups of resources:

  • Application: Vonage App Management resource. Allows CRUD on applications.
  • Voice: Voice call management resource. Allows CRUD on the call.

Create the Vonage Application

Remember the application UUID, because it will be needed to make calls.


  1. Select POST /applications.
  2. Click 'Try out'.
  3. Edit the request body by filling the name and answer_url.
  4. Click 'Execute'.
  5. Check the response code and message.


  1. Click on (POST) Create new application resource.
  2. Fill the name and answer_url.
  3. Click 'Send'.
  4. Check the response code and message.

Create a call


  1. Select POST /voice/calls.
  2. Click 'Try out'.
  3. Update the ApplicationId header with your application identifier.
  4. Edit the request body by filling to, from and answer_url fields.
  5. Click 'Execute'.
  6. Check the response code and message.


  1. Click on (POST) Create an outbound call.
  2. Update the Headers section by filling the ApplicationId` field. 3.. Update the body fields.
  3. Click 'Send'.
  4. Check the response code and message.