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Normalize telephone numbers

Twilio's APIs consistently use the E.164 standard for phone numbers. This format is fine within your code, but it presents a couple of user-facing issues:

  • E.164 is difficult to understand when presented as plain text, such as in an SMS
  • When read aloud by a Twilio Say verb or Say Widget, numbers such as +15095550100 will be read literally as a large number, instead of digit-by-digit. (ex. "Plus fifteen billion, ninety-five million, five hundred fifty thousand, one hundred")

Fortunately, Twilio Lookup enables you to convert a given E.164 phone number into the national format used by that country, which Twilio will read aloud as one would normally say it in their region.

To get started, use the following instructions to create a Function to host your code.

Create and host a Function

In order to run any of the following examples, you will first need to create a Function into which you can paste the example code. You can create a Function using the Twilio Console or the Serverless Toolkit as explained below:

If you prefer a UI-driven approach, creating and deploying a Function can be done entirely using the Twilio Console and the following steps:

  1. Log in to the Twilio Console and navigate to the Functions tab. If you need an account, you can sign up for a free Twilio account here!
  2. Functions are contained within Services. Create a Service by clicking the Create Service button and providing a name such as test-function.
  3. Once you've been redirected to the new Service, click the Add + button and select Add Function from the dropdown.
  4. This will create a new Protected Function for you with the option to rename it. The name of the file will be path it is accessed from.
  5. Copy any one of the example code snippets from this page that you want to experiment with, and paste the code into your newly created Function. You can quickly switch examples by using the dropdown menu of the code rail.
  6. Click Save to save your Function's contents.
  7. Click Deploy All to build and deploy the Function. After a short delay, your Function will be accesible from:
    For example:

The Serverless Toolkit enables you with local development, project deployment, and other functionality via the Twilio CLI. To get up and running with these examples using Serverless Toolkit, follow this process:

  1. From the CLI, run twilio serverless:init <your-service-name> --empty to bootstrap your local environment.
  2. Navigate into your new project directory using cd <your-service-name>
  3. In the /functions directory, create a new JavaScript file that is named respective to the purpose of the Function. For example, sms-reply.protected.js for a Protected Function intended to handle incoming SMS.
  4. Populate the file using the code example of your choice and save.
    Note A Function can only export a single handler. You will want to create separate files if you want to run and/or deploy multiple examples at once.

Once your Function(s) code is written and saved, you can test it either by running it locally (and optionally tunneling requests to it via a tool like ngrok), or by deploying the Function and executing against the deployed url(s).

Run your Function in local development

Run twilio serverless:start from your CLI to start the project locally. The Function(s) in your project will be accesible from http://localhost:3000/sms-reply

  • If you want to test a Function as a Twilio webhook, run:
    twilio phone-numbers:update <your Twilio phone number> --sms-url "http://localhost:3000/sms-reply"​
    This will automatically generate an ngrok tunnel from Twilio to your locally running Function, so you can start sending texts to it. You can apply the same process but with the voice-url flag instead if you want to test with Twilio Voice.
  • If your code does not connect to Twilio Voice/Messages as a webhook, you can start your dev server and start an ngrok tunnel in the same command with the ngrok flag. For example: twilio serverless:start --ngrok=""

Deploy your Function

To deploy your Function and have access to live url(s), run twilio serverless:deploy from your CLI. This will deploy your Function(s) to Twilio under a development environment by default, where they can be accessed from:


For example:

Your Function is now ready to be invoked by HTTP requests, set as the webhook of a Twilio phone number, invoked by a Twilio Studio Run Function Widget, and more!

Respond to a call directly with TwiML

The following Function is one which will tell the user their phone number, in the format that they would expect in normal conversation. This will also work for international phone numbers!

To verify this for yourself, paste the code into the Function that you just made, and set it as the A Call Comes In webhook handler for the Twilio phone number you wish to test. The following instructions will show you how to do so.

Loading Code Sample...

        Convert a number to its national format

        Set a Function as a webhook

        In order for your Function to react to incoming SMS and/or voice calls, it must be set as a webhook for your Twilio number. There are a variety of methods to set a Function as a webhook, as detailed below:

        You can use the Twilio Console UI as a straigforward way of connecting your Function as a webhook:

        1. Log in to the Twilio Console's Phone Numbers page.
        2. Click on the phone number you'd like to have connected to your Function.
        3. If you want the Function to respond to incoming SMS, find the A Message Comes In option under Messaging. If you want the Function to respond to Voice, find the A Call Comes In option under Voice & Fax.
        4. Select Function from the A Message Comes In or A Call Comes In dropdown.
        5. Select the Service that you are using, then the Environment (this will default to ui unless you have created custom domains), and finally Function Path of your Function from the respective dropdown menus.
          Connect a Function as a Messaging webhook using the Function dropdowns
          • Alternatively, you could select Webhook instead of Function, and directly paste in the full URL of the Function.
            Setting a Function as a Messaging webhook using the webhook dropdown option
        6. Click the Save button.

        You can also use the Twilio CLI to assign the Function as the webhook of you phone number. You will need a few prerequisites:

        • Twilio CLI installed and executable from your terminal.
        • Either the E.164 formatted value of your Twilio phone number (+1234567890), or its SID (PNXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX).
        • The full URL of your Function (

        Once you have the CLI installed and the necessary information, run the following to connect the Function to respond to incoming SMS:

        twilio phone-numbers:update +1234567890 \

        If you prefer to have the Function respond to incoming calls instead, run:

        twilio phone-numbers:update +1234567890 \

        You may also use the SID of your Twilio phone number instead of the E.164 formatted phone number:

        twilio phone-numbers:update PNXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX \

        You can also use any of the avilable Twilio SDKs to assign the Function as the webhook of you phone number. You will need a few prerequisites:

        • A local development environment for your language of choice and the associated Twilio SDK installed.
        • The SID (PNXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX) of your Twilio phone number.
        • The full URL of your Function (

        In JavaScript for example, you could execute the following code to assign the SMS webhook of your Twilio phone number. The same logic would apply for assigining to a voice webhook, except that the modified property instead would be voiceUrl:

        // Download the helper library from
        // Find your Account SID and Auth Token at
        // and set the environment variables. See
        const accountSid = process.env.TWILIO_ACCOUNT_SID;
        const authToken = process.env.TWILIO_AUTH_TOKEN;
        const client = require('twilio')(accountSid, authToken);
          .update({ smsUrl: '' })
          .then((phoneNumber) => console.log(phoneNumber.smsUrl));

        Read out phone numbers in a Studio Flow

        This functionality also lends itself well to Studio Flows, where you may share a phone number as part of your IVR. The Say widget doesn't natively read E.164 formatted numbers in the national format, but clever use of the Run Function widget with the following sample code will enable this.

        Create a Studio Flow

        First, create a new Studio Flow. We suggest following the Create Your Flow directions from a Studio tutorial.

        Connect and configure your widgets

        Once you have created a Flow, drag a Run Function and a Say/Play widget onto the Studio canvas. Connect the Incoming Call trigger to the Run Function widget by dragging from the trigger to on top of the widget, and similarly connect the Run Function widget's "Success" condition to the Say/Play widget.

        With the widgets connected, the next step is to configure them.

        Click on the Run Function widget, which should cause the Widget Library to show the configuration options for the widget. Name the widget as you like, and use the drop-down menus to select the Service and path of the Function that you created previously. To wrap up the configuration, click Add under Function Parameters, set the "Key" to From, and "Value" to {{}}. This will cause the phone number of the incoming caller to be passed to the Function as a parameter called From.

        Your configuration and connections should look similar to this:

        Studio Flow showing configuration for a Run Function widget that calls a phone number normalization Function

        Following a similar process, configure the Say/Play widget with your desired name, and paste the following into the "Text to Say" field:

        Hi! Your phone number is {{widgets.<widget-name>.parsed.normalizedPhoneNumber}}.

        Replace <widget-name> with the name of your Run Function widget. This means the Say/Play widget will access the results of the Run Function widget, retrieve a value named normalizedPhoneNumber, and will attempt to read it back to the caller. You can read here to get more context around the parsed property.

        Click Publish to publish your Studio Flow.

        Update your Function's code

        With the Studio Flow published and expecting new behavior from your Function, it will need some slight modifications.

        Edit or replace the body of your Function with the following sample code. Note that it is returning the normalizedPhoneNumber that is expected by the Say/Play widget.

        With your code changes complete, save and deploy your Function.

        Loading Code Sample...
              Provides readable phone numbers to Studio Flows

              Normalize a phone number for the Say Widget

              Provides readable phone numbers to Studio Flows

              Connect and test your Flow

              The last change necessary to test this out is to connect the Studio Flow to your Twilio phone number. You can follow these directions to do so.

              With your Twilio phone number connected to the Studio Flow, you will now be able to call your Twilio phone number, and it will respond by reading out the number you are calling from in a human-friendly manner.

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              Need some help?

              We all do sometimes; code is hard. Get help now from our support team, or lean on the wisdom of the crowd by visiting Twilio's Stack Overflow Collective or browsing the Twilio tag on Stack Overflow.

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