Programmable SMS Quickstart for C# with .NET Core

With just a few lines of code, your .NET Core application can send and receive text messages with Twilio Programmable SMS.

This C# SMS Quickstart will teach you how to do this using our Communications REST API and the Twilio helper library for .NET Core.

In this Quickstart, you will learn how to:

1. Sign up for Twilio and get your first SMS-enabled Twilio phone number
2. Set up your development environment to send and receive messages
3. Send your first SMS
4. Receive inbound text messages
5. Reply to incoming messages with an SMS

Prefer to get started by watching a video? Check out our C# SMS Quickstart video on Youtube.

Sign up for - or sign in to - Twilio

Install the Twilio CLI

We'll need to use the Twilio CLI (command line interface) for a few tasks, so let's install that next.

Run twilio login to get the Twilio CLI connected to your account. Visit https://www.twilio.com/console, and you’ll find your unique Account SID and Auth Token to provide to the CLI.

You can reveal your auth token by clicking on the eyeball icon:

Get a phone number

If you don't currently own a Twilio phone number with SMS functionality, you'll need to purchase one. With the CLI, run:

twilio phone-numbers:buy:local --country-code US --sms-enabled

Select a phone number to add it to your account.

Next, we need to install .NET Core and the Twilio C# Helper Library.

Install .NET Core

You can check if you already have .NET Core installed on your machine by opening up a command prompt or terminal and running the following command:

dotnet --version

You should see something like 2.1.3. If you receive an error message, you can download .NET Core from Microsoft and install it.

Create a new project and add the Twilio NuGet package

Run these commands to create a new .NET project and install the Twilio NuGet package:

mkdir TwilioSend
cd TwilioSend
dotnet new console
dotnet add package Twilio

Send an outbound SMS message with C#

Now that we have .NET Core and the Twilio .NET NuGet package installed, we can send an outbound text message from the Twilio phone number we just purchased with a single API request. Open the file in your new project called Program.cs and type or paste in this code sample, replacing the template code that's already there.

You’ll need to edit this file a little more before your message will send:

Replace the placeholder credential values

Swap the placeholder values for accountSid and authToken with your personal Twilio credentials. Go to https://www.twilio.com/console and log in. On this page, you’ll find your unique Account SID and Auth Token, which you’ll need any time you send messages through the Twilio Client like this. You can reveal your auth token by clicking on the 'view' link:

Edit Program.cs and replace the values for accountSid and authToken with your unique values.

Replace the "from" phone number

Remember that SMS-enabled phone number you bought just a few minutes ago? Go ahead and replace the existing from number with that one, making sure to use E.164 formatting:

[+][country code][phone number including area code]

Replace the "to" phone number

Replace the to phone number with your mobile phone number. This can be any phone number that can receive text messages, but it’s a good idea to test with your own phone, so you can see the magic happen! As above, you should use E.164 formatting for this value.

Save your changes and run this code:

dotnet run

That's it! In a few moments, you should receive an SMS from your Twilio number on your phone.

Are your customers in the U.S. or Canada? You can also send them MMS messages by adding just one line of code. Check out this sending MMS tutorial to see how it's done.

Receive and reply to inbound SMS messages with ASP.NET Core

When your Twilio number receives an incoming message, Twilio will send an HTTP request to a server you control. This callback mechanism is known as a webhook. When Twilio sends your application a request, it expects a response in the TwiML XML format telling it how to respond to the message. Let's see how we would build this in C# using ASP.NET Core.

Create a new ASP.NET Core project

Run these commands to create a new ASP.NET Core project and install the Twilio NuGet package:

mkdir TwilioReceive
cd TwilioReceive
dotnet new mvc
dotnet add package Twilio.AspNet.Core

Create a new controller

In the directory named Controllers, create a new Controller called SmsController.cs and use the following code to create a server that can handle incoming messages.

Save the file, then run your application with:

dotnet run

In your favorite browser, open the URL https://localhost:5001/sms.

If all went well, you should see XML in your browser with the message we'd like to reply with to all our inbound texts. And, yes, that's all the code you need - there's just one more step before everything is wired up.

Configure your Webhook URL

Now, you need to configure your Twilio phone number to call your webhook URL whenever a new message comes in. Just run this CLI command, replacing the phone number with your own Twilio phone number:

twilio phone-numbers:update "+15017122661" --sms-url="https://localhost:5001/sms"

The CLI will start an ngrok tunnel (so Twilio can reach your development machine) and wait patiently for incoming text messages!

Test your application with a text

Make sure your project is running and your ngrok tunnel is running.

With both of those servers running, we’re ready for the fun part - testing our new ASP.NET Core SMS application!

Send an SMS from your mobile phone to your Twilio phone number that's configured with this webhook. Your ASP.NET Core app will process the text message, and you’ll get your response back as an SMS.

Where to next?

Now that you know the basics of sending and receiving SMS and MMS text messages with C# and .NET, you might want to check out these resources.

• REST API documentation
• TwiML reference docs
• Tutorials with full sample applications in C#
• Secure your C# / ASP.NET app by validating incoming Twilio requests

Happy hacking!