Webhooks

Webhooks are an extension of an API, but instead of your code requesting data from Nexmo, Nexmo sends data to you. The data arrives in a web request to your application. A webhook may be the result of an earlier API call (this type of webhook is also called a "callback"), such as an asynchronous request to the Number Insight API. Webhooks are also used to notify your application of events such as an incoming call or message.

Since the Nexmo servers need to be able to send data to your application via webhooks, you need to set up a webserver to receive the incoming HTTP requests. You also need to specify the URL of each webhook on your webserver so that data can be sent to each one.

Webhooks workflow

With webhooks, it's important that the URL to send the webhooks to is configured. When there is data available, Nexmo sends the webhook to your application as an HTTP request. Your application should respond with an HTTP success code to indicate that it successfully received the data.

The process looks something like this:

sequenceDiagram Your App->Nexmo: Configure URL for webhook Note over Your App, Nexmo: Some time later ... Nexmo->Your App: Have some interesting data Your App->Nexmo: 200 OK

Webhooks provide a convenient mechanism for Nexmo to send information to your application for events such as an incoming call or message, or a change in call status. They can also be used to send follow-up information such as a delivery receipt which may become available some time after the request it relates to.

 Which APIs support webhooks?

Information resulting from requests to the SMS API, Voice API, Number Insight API, US Short Codes API, and Nexmo virtual numbers are sent in an HTTP request to your webhook endpoint on an HTTP server. To configure your webhook endpoint, please visit the Nexmo dashboard

Nexmo sends and retrieves the following information using webhooks:

API Name Webhooks usage
SMS API Sends the delivery status of your message and receives inbound SMS
Voice API Retrieves the Nexmo Call Control Objects you use to control the call from one webhook endpoint, and sends information about the call status to another. View the Webhook Reference for more detail.
Number Insight Advanced Async API Receives complete information about a phone number
US Short Codes API Sends the delivery status of your message and receives inbound SMS
Client SDK/Conversation API Real-time Communication (RTC) events are sent to the RTC event webhook
Message and Dispatch APIs Supports both inbound message and message status webhooks

Setting webhook endpoints

Webhooks are used to deliver incoming messages and delivery receipts.

Incoming messages

To set up the webhook used for incoming messages, go to the Your Numbers section of the Nexmo Dashboard. Click 'edit' for the virtual number and set the Callback URL.

You can also use the nexmo-cli to set the incoming messages endpoint for an individual number.

Delivery Receipts

See the Delivery Receipts guide in the SMS documentation.

The Number Insight Advanced API allows you to have the results of a number lookup sent synchronously or asynchronously.

Set the callback argument to a webhook URL to receive the lookup asynchronously.

See Number Insight Advanced Async for more details.

For Voice API requests, webhooks can be set at an application level, when creating a call, or in the actions in an NCCO.

Application-level webhooks

Nexmo numbers that are linked to Nexmo applications will use the answer_url to retrieve an NCCO, and the event_url to send call status information to you. The fallback_answer_url can optionally be configured. This is used when answer_url is offline or returning an HTTP error code. It is also used when an event is expected to deliver an NCCO on event_url, but event_url is offline or returning an HTTP Status code.

You can set these using the Application API, in the Nexmo Dashboard or using the Nexmo CLI tool.

Number-level webhooks

You can set a status webhook for each number you purchase. This will be used to send events to you regarding each number.

These can be set up in the Numbers section of the Dashboard, via the Nexmo CLI or via the Update a Number API call (specifically, the voiceStatusCallback property).

On creating an outbound call

When making a new outbound call, you need to set the answer_url in the call to a URL containing an NCCO. Nexmo's servers will retrieve the NCCO from this endpoint and follow its instructions in handling the outbound call.

Answer URL payload

The payload for the answer_url is:

Parameter Description
to The number being called
from The number making the call
conversation_uuid The UUID of the conversation
uuid The UUID of the leg

Example URL:

/webhooks/answer?to=447700900000&from=447700900001&conversation_uuid=CON-aaaaaaaa-bbbb-cccc-dddd-0123456789ab&uuid=aaaaaaaa-bbbb-cccc-dddd-0123456789cd

Inside an NCCO

Inside an NCCO, the following action types take a webhook URL for use when that action is executed:

  • record.eventUrl - set the webhook endpoint that receives information about the recording for a Call or Conversation
  • conversation.eventUrl - set the URL to the webhook endpoint Nexmo calls asynchronously when a conversation changes state for this conversation action
  • connect.eventUrl - set the URL to the webhook endpoint Nexmo calls asynchronously when a conversation changes state for this connect action
  • input.eventUrl - set the URL to the webhook endpoint Nexmo sends the digits pressed by the callee
  • stream.streamUrl - set an array of URLs pointing to the webhook endpoints hosting the audio file to stream to the Call or Conversation

An Application can receive RTC events via the RTC webhook.

You set the URL of the RTC event webhook when you create the application using your language of choice.

More information on creating an application with RTC capabilities can also be found in the Application API documentation.

There are two webhooks supported by the Messages and Dispatch APIs, the Message Status webhook and the Inbound Message webhook. Message status is inbound on the Message Status webhook and the Message itself is received on the Inbound Message webhook. Setting these webhooks is described in detail in the topic Configuring webhooks for Messages and Dispatch APIs.

Receiving webhooks

To interact with Nexmo webhooks:

  1. Create a Nexmo account.
  2. Write scripts to handle the information sent or requested by Nexmo. Your server must respond with a success status code (any status code between 200 OK and 205 Reset Content) to inbound messages from Nexmo.
  3. Publish your scripts by deploying to a server (for local development, try Ngrok).
  4. Configure a webhook endpoint in the API you would like to use.
  5. Take an action (such as sending an SMS) that will trigger that webhook.

Information about your request is then sent to your webhook endpoint.

Testing webhooks locally

In order to test the correct functioning of webhooks on your locally running application, you will need to create a secure tunnel between Nexmo and your application. You can do this with a secure tunnel application such as Ngrok. See the Testing with Ngrok topic for more information.

Configuring your firewall

If you restrict inbound traffic (including delivery receipts), you need to add the Nexmo IP addresses to your firewall's list of approved IP addresses. You can find more information how to do this in our knowledge base:

Tips for debugging webhooks

Start simple - Publish the simplest possible script that you can think of to respond when the webhook is received and perhaps print some debug information. This makes sure that the URL is what you think it is, and that you can see the output or logs of the application.

Code defensively - Inspect that data values exist and contain what you expected before you go ahead and use them. Depending on your setup, you could be open to receiving unexpected data so always bear this in mind.

Look at examples - Nexmo provides examples implemented with several technology stacks in an attempt to support as many developers as possible. For example code using webhooks see the following:

You can also check the code snippets section of the documentation for the API you are using.

See also