What is an API Request?

Posted on April 18, 2024

API requests are an essential part of modern software development, allowing applications to communicate and exchange data with each other. In this article, we'll explore what API requests are, how they work, and the various components that make up a successful API call.

What is an API Request?

An API request, also known as an API call, is a message sent from a client application to an API endpoint, asking for data or services. API requests allow one application to request and receive data or functionality from another application, enabling communication and integration between different software systems.

How API Requests Work

When making an API request, the client application sends a request to a specific API endpoint, which is identified by a unique URL. The request includes an HTTP method (such as GET, POST, PUT, or DELETE) that indicates the action to be performed on the resource.

Upon receiving the request, the API server processes it, performs the actions or retrieves the requested data, and sends back a response to the client application. The response typically includes a status code indicating the success or failure of the request, along with the requested data or any relevant messages.

Components of an API Call

To make a successful API call, several components are required:

  1. URI or URL: The unique address of the external server or program from which the data or service is being requested.
  2. HTTP verb: The HTTP method (GET, POST, PUT, DELETE) that denotes what action should be performed on the resource, such as retrieving data, creating a new resource, updating an existing one, or deleting a resource.
  3. Header: Additional information that tells the API about the request and the expected response format, such as the content type (e.g., JSON or XML) and any authentication tokens.
  4. API key or access token: A unique identifier used for authentication and tracking purposes, ensuring that only authorized clients can access the API and helping to monitor usage for billing or rate limiting.
  5. Parameters and request body: Data that is sent along with the request to provide information to the API, such as query parameters in the URL or data included in the request body for POST and PUT requests.

By including these components in an API request, a client application can communicate with an API endpoint, retrieve the desired data or perform the requested actions, and receive a response that can be used to update the application's state or display information to the user.

Types of APIs and API Calls


REST (Representational State Transfer) is an architectural style for designing networked applications. REST APIs use standard HTTP methods (GET, POST, PUT, DELETE) to perform operations on resources. These resources are usually represented in JSON or XML format and can be accessed via unique URLs.

REST APIs are simple, scalable, and flexible. They are stateless, meaning that each request contains all the necessary information for the server to process it, without relying on previous requests. This makes REST APIs easy to cache and helps improve performance.


SOAP (Simple Object Access Protocol) is a protocol for exchanging structured information in web services. Unlike REST, SOAP APIs use XML for messaging and follow a more rigid set of rules. SOAP messages are sent over various protocols, such as HTTP, SMTP, or TCP, and typically consist of an envelope, header, and body.

SOAP APIs can be more complex than REST APIs due to their extensive configuration options and the use of XML. However, they offer built-in error handling, support for multiple transport protocols, and strong typing, which can be useful in certain scenarios.

GraphQL APIs

GraphQL is a query language for APIs and a runtime for fulfilling those queries with existing data. Developed by Facebook, GraphQL allows clients to request specific data fields, reducing the number of requests needed and minimizing the amount of data transferred.

With GraphQL, clients send queries to a single endpoint, specifying the desired data fields. The server then responds with exactly the requested data in a structured format. This approach eliminates the need for multiple endpoints and overfetching or underfetching of data, common issues with REST APIs.


Webhooks are a type of API that sends real-time notifications to a specified URL when certain events occur. Instead of constantly polling an API for changes, webhooks allow applications to receive instant updates whenever a relevant event takes place.

Examples of webhook usage include:

  • Payment notifications: A payment gateway can send a webhook notification to an e-commerce application when a payment is processed successfully or fails.
  • System alerts: A monitoring service can use webhooks to notify a DevOps team when a server goes down or an error occurs.
  • Data synchronization: A CRM system can use webhooks to update a marketing automation platform whenever a customer's information changes.

Webhooks are particularly useful for applications that require real-time updates and efficient communication between different systems.

Components of an API Request

When making an API request, several components are included so the API understands the request and can provide the right response. These components include HTTP methods, headers, request bodies, and authentication tokens.

HTTP Methods

HTTP methods, also known as HTTP verbs, show the action to be performed on the specified resource. The most common HTTP methods used in API requests are:

  • GET: Gets a resource from the server. GET requests should only be used to read data and not change it.
  • POST: Creates a new resource on the server. The data for the new resource is sent in the request body.
  • PUT: Updates an existing resource on the server. The updated data is sent in the request body.
  • DELETE: Deletes a resource from the server.


Headers provide extra information about the request and the expected response. Some common headers include:

  • User-Agent: Identifies the client application making the request, such as the name and version of the software.
  • Content-Type: Specifies the format of the data sent in the request body, such as JSON or XML.
  • Accept: Specifies the desired format of the response data, allowing the client to show its preference.

Request Body

The request body contains the data sent from the client to the server. It is mainly used in POST and PUT requests to send the data needed for creating or updating a resource. The format of the request body is usually JSON or XML, and the Content-Type header should be set to match.

API Keys and Access Tokens

API keys and access tokens are used for authentication and authorization purposes. They are unique identifiers that grant clients access to the API based on their assigned permissions. API keys and access tokens help to make sure that only authorized clients can access the API and its resources.

In addition to authentication, API keys and access tokens can also be used to track API usage for billing and monitoring purposes. This allows API providers to enforce rate limits, monitor usage patterns, and bill clients based on their use of API resources.

By including these components in an API request, clients can communicate well with the API, specifying the desired action, providing necessary data, and making sure secure and authorized access to the API's resources.

How to Make API Calls

Making API calls involves several steps, from finding the right API endpoint to handling the response received from the API. Here's a guide on how to make API calls:

Finding the API Endpoint

The first step in making an API call is to find the URI or URL of the server or program you want to get data from. This information is usually available in the API documentation provided by the API provider. The documentation will also have a list of available endpoints and what each endpoint does.

For example, if you want to use the GitHub API to get information about a user, you would look in the documentation and find the endpoint for user information: https://api.github.com/users/{username}.

Formulating the Request

Once you have the endpoint, you need to create the API request. This involves several components:

  1. HTTP method: Specify the action you want to perform on the resource using an HTTP method like GET, POST, PUT, or DELETE. For example, to get user information from the GitHub API, you would use the GET method.

  2. Headers: Include headers to give the API more context about your request and the response format you expect. Common headers are:

    • Content-Type: Specifies the format of the request data, like JSON or XML.
    • Accept: Specifies the desired format for the response data.
    • Authorization: Includes authentication tokens like API keys or access tokens.
  3. API key or access token: Many APIs require authentication to make sure that only authorized clients can access the data. Include your API key or access token in the request, either in the headers or as a query parameter.

  4. Parameters: Some API endpoints allow you to provide parameters to get specific data or to perform certain actions. These can be included in the URL as query parameters or in the request body for POST and PUT requests.

Here's an example of a complete API request to get information about a GitHub user:

GET /users/octocat HTTP/1.1
Host: api.github.com
Authorization: token my_access_token
Accept: application/vnd.github.v3+json

Sending the API Request

To send the API request, you can use an HTTP client library in your programming language of choice or a tool designed for making API requests.

Popular HTTP client libraries include:

These libraries simplify the process of creating and sending API requests and handling the responses.

You can also use tools like Postman or cURL to make API requests. These are especially useful for testing and development purposes, as they allow you to easily create, send, and analyze API requests and responses.

Handling the API Response

After sending the API request, you'll receive a response from the API server. The response will include a status code that shows whether the request was successful or not, and the requested data (if any) in the specified format (usually JSON or XML).

Common status codes include:

  • 2XX codes (like 200 OK) for successful requests
  • 4XX codes (like 404 Not Found) for client errors
  • 5XX codes (like 500 Internal Server Error) for server errors

Here's an example response from the GitHub API for a successful user information request:

HTTP/1.1 200 OK
Content-Type: application/json

  "login": "octocat",
  "id": 1,
  "node_id": "MDQ6VXNlcjE=",
  "avatar_url": "https://github.com/images/error/octocat_happy.gif",
  "gravatar_id": "",
  "url": "https://api.github.com/users/octocat",
  "html_url": "https://github.com/octocat",

In your application, you'll need to handle the response, check the status code to see if the request was successful, and parse the returned data to use it in your application.

By understanding these steps and components of making API calls, you can start integrating data and functionality from external services into your own applications.

Testing API Requests

Testing API requests is an important part of the API development process. It checks that the API works as intended, meets the performance and reliability requirements, and provides a secure and consistent experience for its users.

Importance of API Testing

Testing APIs for functionality, reliability, performance, and security is important to make sure that the API meets the application's and users' needs. Thorough testing helps find bugs, performance bottlenecks, and security vulnerabilities early in the development process, reducing the risk of issues in production environments.

API testing also checks that the API responds correctly to different types of requests, including valid and invalid inputs, and handles errors correctly. By testing various scenarios, developers can make sure that the API is strong and can handle real-world use cases.

How to Test API Calls

To test API calls, developers can use software tools or web services like Postman or cURL. These tools allow developers to make API calls to different endpoints, customize request parameters, and analyze the API responses.

The general process for testing API calls involves the following steps:

  1. Enter the URL of the API endpoint you want to test.
  2. Select the appropriate HTTP method (GET, POST, PUT, DELETE) based on the action you want to perform.
  3. Provide any necessary authentication credentials, such as API keys or access tokens, and set the required headers.
  4. Include any required or optional parameters in the request, either as query parameters in the URL or as part of the request body.
  5. Submit the API request and examine the response received from the API server.
  6. Analyze the returned status code, response time, and the content of the response body to verify that the API is behaving as expected.

By repeating these steps for different API endpoints, request types, and input values, developers can thoroughly test the API and check its quality.

Types of API Tests

There are several types of API tests that developers can perform to check the API's reliability, performance, and security:

  1. Functional testing: This type of testing checks that the API works as expected and returns the correct data. Developers test various API endpoints with different input values and compare the actual responses with the expected results. Functional testing helps make sure that the API meets the specified requirements and behaves consistently.

  2. Performance testing: Performance testing measures the API's response time, throughput, and resource usage under various conditions, such as high traffic or large data volumes. This type of testing helps find performance bottlenecks, optimize the API's efficiency, and make sure that it can handle the expected load.

  3. Security testing: Security testing focuses on finding vulnerabilities and making sure that the API is protected against common attacks, such as SQL injection, cross-site scripting (XSS), and authorization bypass. Developers test the API's authentication and authorization mechanisms, validate input data, and check for proper error handling to minimize security risks.

  4. Reliability testing: Reliability testing checks the API's ability to handle errors, edge cases, and unexpected inputs correctly. This includes testing for proper error responses, timeouts, and the API's ability to recover from failures. Reliability testing helps make sure that the API remains stable and predictable even in exceptional situations.

By conducting these different types of tests, developers can verify that the API meets the required quality standards and provides a reliable, performant, and secure service to its users.

Real-World Examples of API Calls in Action

API calls are used in many real-world applications to enable communication between different software systems. Let's look at some common examples of how API calls are used in practice.

Booking a Flight

When you use a travel website to book a flight, the website often interacts with the airline's API to get real-time information about available flights. Here's how the process might work:

  1. You enter your desired travel dates, departure airport, and destination on the travel website.
  2. The travel website sends a GET request to the airline's API endpoint, passing along your search parameters as part of the URL or query parameters.
  3. The airline's API server receives the request, searches its database for flights matching your criteria, and sends back a response containing a list of available flights, along with information such as prices, departure and arrival times, and flight numbers.
  4. The travel website parses the API response and displays the available flights to you, allowing you to select and book your desired flight.

By using API calls, the travel website can provide you with up-to-date flight information without having to maintain its own database of flights.

Posting on Social Media

Social media platforms like Facebook, Twitter, and Instagram provide APIs that allow third-party applications to interact with their services. When you post something on a social media platform through an app, the app uses the platform's API to send your post to the platform's servers. Here's how it works:

  1. You compose a new post in the app, which could include text, images, or videos.
  2. When you submit the post, the app sends a POST request to the social media platform's API endpoint. The request includes the content of your post and any necessary authentication tokens.
  3. The API server receives the request, verifies your authentication, and processes the post data.
  4. If the post is valid, the API server stores the new post in its database and sends back a response to the app indicating that the post was created successfully.
  5. The app receives the response and displays a confirmation message to you.

By using the social media platform's API, the app can allow you to create posts without having to build its own backend infrastructure for storing and processing post data.

Processing Payments

When you make a purchase on an e-commerce website, the website often uses a payment gateway's API to securely process your payment. Here's an example of how the payment process might work:

  1. You select the items you want to purchase and proceed to the checkout page on the e-commerce website.
  2. You enter your payment details, such as your credit card number and billing address.
  3. When you submit the payment form, the e-commerce website sends a POST request to the payment gateway's API endpoint. The request includes your payment details and the total amount to be charged.
  4. The payment gateway's API server receives the request and securely communicates with the payment provider (such as the credit card company) to process the transaction.
  5. If the payment is approved, the payment gateway sends a response back to the e-commerce website indicating that the payment was successful. If the payment is declined, the API sends back an error response.
  6. The e-commerce website receives the API response and displays a confirmation message to you, letting you know whether the payment was processed successfully.

By using a payment gateway's API, the e-commerce website can securely process payments without having to handle sensitive payment information directly.

These are just a few examples of how API calls are used in real-world applications. APIs enable different software systems to communicate and exchange data seamlessly, making it possible to build complex applications that leverage the functionality of multiple services.

Key Takeaways

  • API requests are messages sent from client applications to API endpoints to request data or services
  • API requests include components such as HTTP methods, headers, request bodies, and authentication tokens
  • REST, SOAP, and GraphQL are different types of APIs with their own architectural styles and communication protocols
  • Making API calls involves finding the endpoint, formulating the request, sending it, and handling the response
  • Testing APIs is crucial to ensure functionality, reliability, performance, and security, and can be done using tools like Postman or cURL