What is an API Call?

API calls are what make modern apps feel fast, responsive, and connected. They enable seamless communication between systems, which not only improves the user experience but also helps businesses scale by automating tasks and connecting tools without needing to rebuild everything from the ground up.

While APIs can be used in countless ways across software, systems, and devices, here are some of the most common real-world applications:

• Integrating third-party services: API calls enable your app to communicate with other platforms, pulling in features or data you don’t want to build from scratch.
  • Example: Embedding Google Maps into a ride-sharing app.
• Automating workflows: API calls allow different tools to trigger actions or share data automatically, creating automated workflows that don’t require manual intervention.
  • Example: Syncing customer data between a CRM and an email marketing tool.
• Accessing cloud resources: API calls are how apps fetch, upload, or manage files stored in cloud systems.
  • Example: Pulling documents from cloud storage platforms like AWS S3.
• Enhancing user experiences: API calls make apps feel more dynamic and responsive by retrieving real-time information or updates as things happen.
  • Example: Displaying real-time stock prices on a financial app.

REST (Representational State Transfer) APIs are one of the most common ways apps and systems communicate over the internet. They’re popular because they’re simple, lightweight, and built on web standards like HTTP, making them easy to use with modern web and mobile technologies.

A REST API call is a request sent from a client (like a web browser or mobile app) to a server to get or change information, such as retrieving user data, submitting a form, or updating a product listing. These calls are designed to be stateless and efficient, utilizing standard methods such as GET, POST, PUT, and DELETE.

While there are other types of APIs, including GraphQL, SOAP, or gRPC, REST stands out for its flexibility, wide support, and ease of integration.

To work properly, REST APIs follow a specific set of design rules that keep them scalable, consistent, and easy to use. These six key principles are:

Each API request from a client must include all the information the server needs to understand and process it. The server doesn’t keep track of past requests or session data. This makes interactions simpler and more scalable, since each request is treated independently.

The client (like a web browser or mobile app) and the server (which stores and processes data) are kept separate. This separation allows each side to evolve independently. The frontend can change without affecting how the backend works, and vice versa.

API responses can be marked as cacheable so clients or intermediary systems (like a browser) can reuse them instead of making the same request again. This improves performance and reduces server load, especially for data that doesn’t change often.

REST APIs use a consistent structure for how data is requested and sent. This includes things like using standard HTTP methods (GET, POST, PUT, DELETE), clear and consistent URLs to identify resources, and predictable response formats. This uniformity makes APIs easier to learn and integrate with.

A REST API can operate across multiple layers, including proxies, gateways, or load balancers between the client and the actual server. Each layer works independently, and the client doesn’t need to know what’s in between. This allows for better scalability, security, and flexibility.

This is the only REST principle that isn’t required. In some cases, a REST API can send executable code (like JavaScript) to the client as part of the response. This lets the client add new features or handle certain tasks without needing to be updated itself. However, it can also add complexity and potential security concerns. In many cases, especially where performance and predictability are important, developers choose not to use it. Most REST APIs work just fine, and often more securely, without sending code to the client.

APIs come in different types or groupings based on the kind of action they perform, and understanding these distinctions is important for using them effectively. To build on the restaurant analogy, when you speak to a waiter, you’re not always just ordering a dish. You might ask for a modification to your meal or request a completely new one if the original doesn’t suit you.

Similarly, API calls are designed to handle different tasks: some retrieve information, others create new data, some replace existing data entirely, and others make partial updates. Recognizing these different types of API calls helps developers communicate precisely with servers, ensuring the right action is taken and making applications more efficient and reliable.

There are many types of API calls, each designed for different purposes and depending on the API style being used. However, when it comes to REST APIs — the most widely used kind — there are four main types of calls that you’ll encounter most often:

A GET request retrieves data from a server without altering it. For instance, fetching a user’s profile details from a database. This method is safe and commonly used for read-only operations.

A POST request submits data to a server to create a new resource. Examples include submitting a form on a website or uploading a file to a cloud service. Unlike GET, POST requests can change server state and are not idempotent — meaning if you send the same POST request multiple times, it could create multiple records instead of just one.

PUT requests replace an entire resource with new data. With a PUT request, you send the complete updated resource version. If the resource doesn’t exist, PUT may create it (depending on API design). Repeated calls yield the same result (e.g., sending the same data twice won’t change the outcome after the first update).

A PATCH request modifies part of a resource. You send only the fields you want to change, and repeated calls might have different effects (e.g., incrementing a value twice).

Imagine being at a restaurant where you can’t place an order. Without that crucial step, the kitchen wouldn’t know what you want — or that you’re even there.

In the digital world, API calls serve that essential role. They’re how applications communicate their requests and deliver responses, making it possible for systems to work together seamlessly. Without API calls, apps wouldn’t be able to share data or perform the actions users expect, which is why they’re so important to everything from everyday apps to complex IT systems.

Let’s explore some of the key benefits that API calls bring to modern software and businesses.

• Make systems work together: API calls connect different apps and services, even if they weren’t originally designed to work with each other.
• Speed up development: Developers can use existing APIs to quickly add features or link to data, saving time and effort.
• Keep data secure: APIs use security measures like special access tokens to make sure only authorized users can exchange information.
• Help different technologies communicate: APIs act like translators, letting apps, devices, and software written in different languages understand each other.
• Create common standards: Many APIs follow agreed-upon rules (like REST or SOAP), making communication predictable and reliable.
• Support modern app design: Today’s apps often break into smaller parts called microservices that rely on APIs to talk to each other inside the system.

Just as you wouldn’t go to a restaurant that doesn’t take orders, digital systems can’t deliver what you need without API calls to tell them what to do. Whether you’re checking the weather on your phone, streaming a movie, or automating complex workflows and connecting disparate apps, API calls are working behind the scenes to make it all possible.

To ensure the efficiency and security of your APIs, use a trusted API platform with a track record of success. Contact MuleSoft today to get started.