Understanding the core components of an API is essential for setting them up effectively and ensuring they function as intended. Without this knowledge, it would be difficult to leverage APIs correctly in your projects.
In this guide, we’ll break down each part of an API, explaining what it does, how it works, and how you can use it. We’ll also explore real-world examples that highlight the importance and functionality of each component.
But first, let’s take a step back for a high-level overview of APIs.
How Do APIs Work?
API stands for “Application Programming Interface.” At its core, an API is a piece of code that enables different applications, databases, or services to communicate with one another.
For APIs to function properly, they follow specific standards and protocols, ensuring interoperability across various systems. While there are different protocols, the fundamental principle remains the same: setting up an API allows consistent communication between applications, regardless of the tools in use.
So, what does “communication” mean here? Unlike a human conversation, APIs allow software to make requests and exchange data in structured ways.
In simple terms, APIs enable clients (such as applications) to send requests to servers, which then respond with the requested data. This interaction framework is crucial for the secure and organized sharing of data between systems.
Now, let’s return to our original question: what are the key components of an API?
Let’s dive in!
API Clients
An API client is any application that makes an initial data request. This could be a web browser, a mobile app, a SaaS platform, or another software. The client assembles the data needed to make the request, which is then sent to the server. The client also controls when requests are sent, which could be triggered by user actions, like clicking a button, or by automated events, such as a database query or timed action.
API Requests
API requests are designed for interoperability, meaning they follow a consistent structure, so any platform supporting the protocol can handle them. An API request has five basic components:
Endpoints
An endpoint is the URL where the API request is directed, typically including the server domain, the resource being accessed, and the API version. For example, to access lion data on a zoo API, the endpoint might look like:
https://api.example.com/v2/lions
Additional filters or information can be added as query parameters in the URL. For instance, to request data on a lion named Franky, we could use:
https://api.example.com/v2/lions?lionName=Franky
Methods
Methods define the action the server should take with the data. Common HTTP methods in REST APIs include:
- GET – Retrieve data.
- POST – Create new data.
- PUT – Replace existing data or add new data.
- PATCH – Modify specific data fields.
- DELETE – Remove data.
Parameters
Parameters add detail to API requests. We’ve already seen query parameters in the URL. There are also:
- Path parameters – Extend the URL to specify data attributes.
- Query parameters – Add filters, sorting, or pagination.
- Header parameters – Include metadata like authentication details.
- Request body parameters – Used in PUT, PATCH, or POST requests to modify or create data.
To change Franky’s favorite food to “Chicken,” we’d include it in the request body.
Headers
Headers provide additional context, such as:
- Authentication information.
- Caching preferences.
- Formatting and response type expectations.
Request Bodies
The request body is where new data or updates are provided, especially in PUT, PATCH, and POST requests.
- A PUT request typically includes all current values and new ones.
- A PATCH request only includes fields to be updated.
API Server
An API server hosts and manages the API. It defines:
- Available endpoints and operations.
- How requests are handled, validated, and authenticated.
Data structure rules in two layers:
- Data Layer: Where data is stored and managed (e.g., a database).
- Process Layer: Where business logic is applied to data, like generating invoices.
The server processes requests according to the rules in these layers, ensuring actions follow the correct permissions and workflows.
API Response
The server’s response includes three parts:
Status Code
- A three-digit code indicates the request’s success:
- 200: Success.
- 201: Success, with new data created.
- 400: Bad request syntax.
- 401: Unauthorized.
- 404: Not found.
- 500: Server error.
Response Headers
These can:
- Set cookies.
- Indicate required authentication.
- Provide response format information.
Body
The response body contains the requested data, typically used in GET requests.
4 Types of APIs
There are several types of APIs, each designed for different developers and project needs:
- Private APIs: These internal APIs are built for use exclusively by a company’s own developers.
- Public APIs: Accessible to anyone, though some may require a fee, these APIs are openly available for use.
- Partner APIs: Designed for specific business relationships, these APIs support native integrations with other platforms.
- Composite APIs: These combine multiple APIs to handle related or interdependent tasks in a single call, improving performance over multiple individual requests.
