Rate this page:

Manage application state with cookies

Due to the ephemeral nature of Functions, application state for purely serverless apps has previously been difficult to manage, or required storing such information in a remote database. Luckily, with access to cookies with Runtime Handler version 1.2.1 and later, you can now maintain limited state in your apps through cookies!

Let's create a Function named state that leverages per-phone number cookies to store some application state, just like you would with a more traditional, server-based solution! Use the following directions to create a Service and your state Function:

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!

Store application state in a cookie

Now that you have your state Function, copy over the following code sample, save the Function, and deploy your Service.

Loading Code Sample...

        Add counter state to an SMS response

        For Twilio SMS, cookies are scoped to the "conversation" between two parties -- you can have a unique cookie for each To/From phone number pair. For example, you can store a unique cookie for any messages sent between 415-555-2222 (your number, for example) and 415-555-1111 (the phone number your Function is a webhook for), which will be different from the cookie used between 415-555-3333 and 415-555-1111.

        The code here is accepting an incoming Message webhook request, and checking for an incoming cookie named count. If that cookie is not present, count is initialized to 0, the user message is formatted to indicate the start of a conversation, and the count is incremented then set as a cookie along with the response to the sender. If count is already present, its value is included in the message, incremented, and set so that subsequent messages can continue to store the ever-increasing value of count.

        To test this and observe your stateless Function managing to track state with cookies, you'll need to set your deployed state Function as the webhook for your Twilio phone number, as shown next.

        Cookies created in this specific scenario (Twilio forwarding SMS messages to your Function or server) are limited to a maximum lifetime of four hours, so if a conversation remains idle for more than four hours, it will be automatically cleared. If you require longer-lasting state, you will need to store it in an external source such as a database.

        In any other scenario, cookies set by your Function are only subject to the usual limitations.

        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));

        Validate that it works

        Now that your Twilio phone number is directing incoming SMS messages to your Function, try sending a short message to your Twilio phone number.

        You will receive an initial response of Hello, thanks for the new message!, and any subsequent messages you send will then receive a response of Your current count is 1, Your current count is 2, and so on.

        Set state attributes

        Cookies support several attributes, which allow you to define aspects such as duration, security, and more. You can set these using the third parameter to setCookie. For example, given the existing call:

        response.setCookie('count', (count + 1).toString());

        You could modify the count cookie to last for a maximum of 30 minutes (1800 seconds) by setting the Max-Age attribute like so:

        response.setCookie('count', (count + 1).toString(), ['Max-Age=1800']);

        Remove or reset state

        By default, session cookies persisted by Twilio SMS only last for four hours at most, and you cannot exceed this limit. However, it's perfectly valid to remove a cookie at any time to fit your application's needs.

        For example, you could clear the count from the previous example once a condition is met, as shown in this sample:

        Loading Code Sample...

              Clear counter state from an SMS conversation

              Validate state reset

              If you save and deploy this new code instead, you should have a very similar interaction with your Twilio phone number. After sending a message, you will receive an initial response, and any subsequent messages you send will then receive a response of Your current count is 1, Your current count is 2, and so on.

              The difference is that after reaching a count of five and sending another message, you'll receive You've reached the end of the count!. If you try to message again, you'll find yourself in a completely new conversation. This is a handy way to end interactions, such as if your application has successfully helped a customer, or if your application is a game that the user has won or lost.

              These examples demonstrate adding a single state value as a cookie, but you are free to add more to support your application needs!

              Keep in mind, there are limitations on how many cookies can be set, how large they can be, and how long they can persist until expiring.

              Curious about what else you can build by using cookies to add statefulness to your Functions? Check out this blog article to see how you can build your own Wordle clone purely with Functions and Assets!

              Rate this page:

              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.

              Loading Code Sample...

                    Thank you for your feedback!

                    Please select the reason(s) for your feedback. The additional information you provide helps us improve our documentation:

                    Sending your feedback...
                    🎉 Thank you for your feedback!
                    Something went wrong. Please try again.

                    Thanks for your feedback!