What Is an API Call and How Do They Work?

By Boomi

To ensure apps communicate effectively, programmers rely on API calls and gateways. In this post, we’ll explain what they are, and how they work together to connect vital services.

In previous posts, we’ve discussed what an API is and how it works in a business environment, and talked about API management. As a brief refresher, an application programming interface (API) is a series of protocols that enables interaction between a pair of applications. It’s a type of software infrastructure that delivers requests to a server, then provides the response back to the client.

APIs are crucial tools in the world of software development. They serve as basic templates or building blocks for developers, who don’t need to start from scratch with their code every time they develop a new application. In this way, APIs save developers a significant amount of time. They take these reusable blocks of code and implement them in new ways when developing software, knowing that the framework for cross-application synergy is already designed for them.

In some cases, programmers even develop APIs for commercial purposes that they can sell as intellectual property to other developers, who then use those APIs in their own software. Needless to say, APIs are critical in the increasingly complex world of software as a service (SaaS) platforms and customized tech stacks. As such, their calls are also becoming more complex.

What is an API call?

In short, API calls make it possible to retrieve just about any kind of information through applications and web searches, so long as the request is validated through the API gateway. An API call is what happens when a developer adds an endpoint to a URL and submits a request to the server. “Endpoint” is a term that refers to the end of a communication channel. It could be a particular server or other location from which the API gets the resources requested by users.

The steps to an API call are as follows:

  • The program submits a request for information to the API. This “request” could be a simple search, a login attempt, etc.
  • The API examines the validity of the request and forwards the call to an external program.
  • The API receives a response from the external program, then passes the data back to the requesting program.

API Call Examples

Take, for example, the process of logging into an app. The first time a user opens an app, it prompts them for an email/username and password. Submitting these details involves making an API call. The server’s response is to allow access, after it validates the user’s login credentials.

Another example of an API call is checking a website’s availability for reservations. A user who wants to book a hotel room for a certain number of days would put those days into the field and hit “submit.” The API examines the request, gathers information about availability for those dates and returns that information to the user. It’s a simple querying process, and the API makes communication between systems seamless.

Even sharing photos to Facebook or Instagram involves the use of a basic API. The request is to upload the photo, and the API confirms with the Facebook server that it is a valid request. Once the server authorizes the request, the upload proceeds. In this way, API calls are gatekeepers.

API Gateways and Their Role in API Management

The process of an API call is made possible in part by API gateways. An API gateway is a type of API management tool positioned between the client and the back-end service, accepting API calls and returning the relevant information.

An API gateway funnels incoming requests through the system. The specific function of that gateway will vary from one application to another. Some functions include:

  • Authentication: A developer who wishes to prevent their APIs from being overused can create authentication services and rate limiting with their API gateways.
  • Analytics: Developers who want to understand the ways people use their APIs can add analytic and monitoring functions via an API gateway.
  • Monetization: For developers who have monetized an API, the API gateway can implement a billing system.

Perhaps the biggest development in modern API gateways is the inclusion of microservices. A single request from a client might require API calls to dozens of different applications. Here, the API gateway can serve as something akin to a phone operator, handling all calls from clients, then routing them to the proper location, ensuring requests result in efficient return of information — with much greater levels of organization.

The versatility of API gateways and how they help process specific types of requests in API calls makes them very popular among developers. Used appropriately, they’re a critical step in creating synergies among connected apps and digital services.

Using Boomi for API Management

Boomi API Management makes it easier for business owners to configure, test and deploy APIs and track their usage and health, and better engage API developers. Boomi’s integration platform as a service (iPaaS) approach facilitates seamless API communication across your entire tech stack, to ensure there’s no loss of data transfer efficiency or integrity, no matter how many calls or gateways are involved.


Learn more about the benefits of an iPaaS-led approach to API management in our eBook, “Simplifying API-led Connectivity With a Modern Integration Platform.”