3 Types Of User Communication APIs and When To Use Themby@courier
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3 Types Of User Communication APIs and When To Use Them

by CourierJanuary 7th, 2022
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If you’re an engineer who’s been tasked with planning out your application’s communication strategy, this post will help you map out the landscape. You’ll come away understanding the three core types of user communication APIs and in which circumstances you should use them to create the best possible end-user experience.

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As modern applications have become increasingly feature-rich and performant, user expectations are at an all-time high. Failure to communicate key information or displaying out-of-date information frustrates users and causes a loss of trust. Think about the last time you ordered something online: if you didn’t receive your order confirmation within seconds, you probably began to worry that something went wrong. Users require product transparency for consistent use.

Luckily for developers, a proliferation of new APIs have been developed to help provide features such as real-time order update emails, push notifications based on in-app activity, or live chat with sales and support. Communications APIs are becoming increasingly specialized, with each type being more or less suited to certain tasks.

If you’re an engineer who’s been tasked with planning out your application’s communication strategy, this post will help you map out the landscape. You’ll come away understanding the three core types of user communication APIs and in which circumstances you should use them to create the best possible end-user experience. We’ll also show you how using the right APIs in the right places will streamline your own day-to-day work.

Let’s get into it!

Planning Your Communications API Strategy

The best outcome any engineer can hope for is that your communications strategy is so smooth, it isn’t even noticed. For the end-user, it just works exactly when it’s supposed to work, the way it’s supposed to work. For your own internal teams, everyone has the ability to craft the messaging they need and send it when they need it, without unnecessary bottlenecks that can often impact your own engineering time.

In a marketplace application, for instance, users need to get an automated push notification or email every time someone comments on an item they’re selling. The marketing department also wants to send email campaigns to everyone who has purchased an item in the past six months to let them know there’s a sale coming up. When a buyer’s checkout fails, they might need to message your sales or support team to get help and complete the transaction.

All of these are very different examples that will need to use a different type of communications API to get the job done.

Exploring The Three Types

Communications APIs are segmented not only by the functionality they provide and how immediately they need to respond to user actions but also often by which teams at the company will need to use them to send messages.

App-to-user APIs are highly customizable, instant communications sent by engineering as integral parts of the application experience, such as push notifications about likes or comments. Brand-to-user APIs collect data and give the company, particularly marketing and product teams, the ability to send users targeted messages individually or en masse. User-to-user APIs facilitate live chat either among app users or with someone at your company, such as sales or support.

Let’s discuss the strengths and weaknesses of the three types of APIs, and see some commonly-used third-party providers for each.

App-to-user APIs

App-to-user APIs are transactional messages that are embedded into the application code. These APIs are often the most mission-critical of the three, as they form a core part of the application experience. For instance: your rideshare has arrived, your order was received, you have just been added to this chat room; here is your one-time password for login. These types of communications tend to be time-sensitive and are designed to send immediately when the trigger events occur.

A robust App-to-user API will provide multi-channel communication (email, SMS, and push notification), complex routing, and easy opt-in and opt-out for users. Most can be heavily automated as well. For instance, when a new user is created via Auth0, a welcome push notification can be automatically sent.

App-to-user APIs are typically instrumented and used by engineering teams. Companies who have the resources may choose to build their own App-to-user API infrastructure, which we have a guide on how to do here. Courier also provides a ready-to-use App-to-user API infrastructure.

Brand-to-user APIs

Brand-to-user communication happens any time your company has a message for a specific group of users. Maybe the product team noticed that a user got partway through the sign-up flow but didn’t hit the “complete” button. Maybe marketing wants to tell everyone in New York about an upcoming in-person event.

Braze and are two examples of out-of-the-box Brand-to-user APIs. Engineering implements API calls in the application code that log information about user behavior, which then gets sent to a separate dashboard other teams at the company can access. Anyone on those teams can then use that data to craft and send messages to specific subsets of users. For instance, users who didn’t complete the sign-up flow, or who live in New York. Brand-to-user APIs save engineering time because, once the initial API calls are instrumented, any team who needs to send campaigns or needs to access that data can do so easily and independently.

While Brand-to-user APIs make it easy for anyone at the company to send messages to users, they typically aren’t configurable enough to power core parts of the application experience. Messages can go out minutes to hours after user criteria for the message have been met. There can also be implementation delays any time you want to send messages based on a different set of criteria than you were using before—new API calls in the app mean the data needs time to populate before they can be used.

While this trade-off is often worthwhile for marketing and product communications, App-to-user APIs (discussed above) are a much better fit when you need fine control over messaging content or timing within engineering.

User-to-user APIs

User-to-user communication APIs facilitate active conversations among two or more individuals—either between a user and someone on your own internal staff or from one app user to another.


upport tickets, for instance, are a type of User-to-user API, as are live chat boxes that let customers have direct conversations with your support or sales teams. Likewise, two users in a marketplace might need to message each other to offer bids or send along with shipping information.

While these are possible services to build out in-house, most companies opt to save time by going with a ready-to-use SaaS solution, such as Intercom, Zendesk, or Sendgrid.


Most applications will use more than one type of user communications API for different parts of the user experience. Your application may very well use all three!

App-to-user APIs provide part of the application’s core functionality. These APIs are highly customizable and provide instant user communication that is tightly coupled with your application code. Marketing and product teams will often want a Brand-to-user API implementation that makes it easier to see user data and send updates to users. User-to-user APIs give customers access to back-and-forth communication either among each other or with company support or sales teams.

When you’re thoughtful about your communications strategy, you can create a seamless experience for users while also enabling everyone on your team to save time and do their best work.

Read on for more information on building user communication API infrastructure:

Illustration by Rebekka Dunlap