It’s no secret that I think Microsoft Teams is an awesome product. I’ve written in the past about how I believe Teams is a great enabler for making people more productive and brings the right tools together in a place that makes a lot of sense.
What are messaging extensions?
Message extensions are available when you are creating a chat message (either a new conversation, or when replying to an existing message). Message extensions assist you by inserting content into the chat message you are composing.

Below is the Giphy messaging extension that allows you to search for an animated image and insert it into your message.


Why develop a messaging extension?
One of the resounding benefits of the Microsoft Teams client is being able to extend the out-of-the-box capabilities and integrate with your existing line of business (LOB) applications. Usually the benefit gain in integrating LOB applications into Teams is that it reduces the context switching for users and they spend more time actually getting work done, and less time moving between application, copying/pasting data or links.
Take a CRM application as an example, if you are discussing a customer in a conversation in Teams and needed to explain where that customer was located, or what the contact details were. The steps you would normally go through would be to open your CRM application, search for the customer, find the relevant details, then cut and paste multiple fields of text switching back and forth between the customer details in the CRM app and the conversation in Teams.
By extending Teams with Messaging Extensions, it is possible to provide an integration into your CRM system that would allow a user to search for a customer in Teams while composing a chat message, select the customer and have the details formatted nicely and inserted in the chat message all without having to leave Teams or even open the CRM application.
When you look at the core LOB applications within your organisation there are some key integrations such as this that can bring about real productivity gains.
Where to start with messaging extension development?
Developing messaging extensions for Microsoft Team (overview)
Training Content / Bots, Messaging Extensions and Cards (Github)
The Timely Teams App
You may be interested in a walk-through article I wrote on creating a messaging extension that provides timezone conversions. This example goes an extra step of combining messaging extensions with task modules to get full control of the UI and functionality of the pop-up dialog https://camerondwyer.com/2019/09/09/how-to-create-a-microsoft-teams-messaging-extension-pop-up-dialog-with-a-custom-ui/