What are Request Headers and Request Body of an API?

Request Headers & Request body of an API


API stands for Application Programming Interface. It is a set of rules and protocols that allows different software applications to communicate and interact with each other. APIs act as intermediaries, enabling different systems to request and exchange data, services, or functionalities seamlessly.

They play a crucial role in modern software development, facilitating integration, scalability, and interoperability across various applications and platforms.

The role of APIs in modern software development can be summarized as follows:

  1. Data Access and Integration: APIs enable applications to access and retrieve data from external sources, databases, or other applications. They facilitate data integration and synchronization, allowing applications to work with data from multiple sources efficiently.
  2. Service Interaction: APIs provide a standardized way for applications to access services offered by other systems. This includes functionalities like payment processing, authentication, messaging, and more, without having to implement these services from scratch.
  3. Cross-Platform Compatibility: APIs promote cross-platform compatibility, allowing applications to run on different operating systems, devices, or browsers. Developers can build applications that work on various platforms by leveraging APIs with consistent interfaces.
  4. Modularity and Reusability: APIs encourage modular design and code reuse. Developers can create reusable components or libraries encapsulated behind APIs, reducing development time and effort when building new applications.
  5. Scalability and Microservices: APIs are a fundamental component of microservices architecture. By breaking down monolithic applications into smaller, independent services, APIs allow developers to scale and deploy specific services independently.
  6. Third-Party Integrations: APIs enable seamless integration with third-party services and platforms. This empowers developers to leverage specialized functionalities and services without building them from scratch, thus accelerating the development process.
  7. Developer Ecosystem: APIs foster developer ecosystems, attracting third-party developers to build applications and extensions that extend the functionality of a platform or service.
  8. Easier Software Maintenance: With APIs, developers can update or replace underlying components or services without affecting the applications that use them, simplifying software maintenance and upgrades.
  9. Rapid Prototyping and Innovation: APIs provide a way to prototype and experiment with new ideas rapidly. Developers can test new features or functionalities without interfering with the existing codebase.
  10. Standardization and Interoperability: APIs promote standardization, allowing developers to build applications using well-defined interfaces. This improves interoperability between different systems and reduces integration complexities.


cURL (pronounced “curl” or “kurl”) is a command-line tool and library for making HTTP requests to interact with web servers and transfer data. It stands for “Client for URL” and is widely used in the development and testing of web applications and APIs. cURL supports various protocols, including HTTP, HTTPS, FTP, FTPS, SCP, SFTP, LDAP, and more.

A cURL request is a simple text-based command that you can execute in the terminal or command prompt of your operating system. It allows you to make HTTP requests to a specific URL and perform various operations, such as retrieving data, sending data, or executing specific HTTP methods like GET, POST, PUT, DELETE, etc.

The basic syntax of a cURL request is as follows:

curl [options] [URL]

Here are some common cURL options:

  • X : Specifies the HTTP method (GET, POST, PUT, DELETE, etc.).
  • H : Sets custom HTTP headers.
  • d : Sends data in the request body (usually used with POST requests).
  • i : Includes response headers in the output.
  • o : Saves the response output to a file.
  • u : Sets username and password for authentication.
  • k : Allows insecure SSL connections.

Here are few examples:

  1. curl -X POST -H "Content-Type: application/json" -d '{"name":"John", "age":30}' https://api.example.com/users
  2. curl https://api.example.com/data

cURL is a powerful and flexible tool for testing APIs, debugging network issues, and automating HTTP requests in scripts and command-line environments.

Anatomy of an API Request: Understanding Its Key Components:

An API request typically consists of several components that convey specific information to the server. These components help the client and the server understand and fulfill each other’s requirements.

We will use popular Github API to explain the API components.

  1. API Endpoint: The API endpoint is the URL that identifies the resource or action you want to access. In this case, we want to retrieve information about a user, so the endpoint is the GitHub API’s user API endpoint. API Endpoint: https://api.github.com/users/{username}/events?type=public Replace {username} with the GitHub username of the user you want to fetch information for.
  2. HTTP Method (Verb): Since we want to retrieve data, we’ll use the HTTP GET method. Common HTTP methods include:
    • GET: Requests data from the server (read-only operation).
    • POST: Sends data to the server to create a new resource.
    • PUT: Updates an existing resource with new data.
    • DELETE: Deletes a resource from the server.
  3. Request Headers: Common headers sent along with the API request include:
    • User-Agent : Identifies the client making the request (often set to the name of the application or user agent string).
    • Authorization : If accessing authenticated endpoints, an access token may be included in this header.
    • Accept : Specifies the expected response format (e.g., application/json to request JSON data). Example Request Headers where userName is Arunshaik2001
  1. Request Payload: The request payload contains data sent to the server in the request body for methods like POST, PUT, or PATCH. In this example, we are using a GET request, so there is no request payload.
  2. Query Parameters: Additional data sent as part of the URL to modify the request or filter the response. In this example, there are no query parameters.
  3. Response Headers: Response headers provide additional information about the server’s response. Some common response headers are:
    • CORS headers (Cross-Origin Resource Sharing): CORS headers control whether the API can be accessed by clients from different origins (websites). These headers help enforce security policies to prevent unauthorized cross-origin requests.
    • Security headers: Headers like X-Content-Type-Options , X-XSS-Protection , and Strict-Transport-Security help protect against security vulnerabilities, like content type sniffing, cross-site scripting, and man-in-the-middle attacks.
    • Cookies & Caching headers: Headers like Set-Cookie , Cache-Control , and Expires manage cookie storage and cache settings for the response.
    • X-Frame-Options headers: This header helps protect against clickjacking attacks by specifying whether the page can be displayed within a frame or iframe. Example Response Headers
  1. Response Body: The response body contains the actual data returned by the server in response to the API request. The format of the response body depends on the API and the endpoint. Common response formats include JSON, XML, HTML, or plain text. HTTP Status Codes for Different Cases:
  • 200 OK: The request was successful, and the server returned the requested data. The response body contains the data.
  • 204 No Content: The request was successful, but there is no data to return. It’s typically used for successful DELETE requests.
  • 400 Bad Request: The server cannot process the request due to a client error, like missing or invalid parameters.
  • 500 Internal Server Error: The server encountered an error while processing the request, indicating a server-side issue.

You can simulate Status codes using Requestly

This is the Response Body looks like:

How Requestly can help in API testing?

Requestly will help developers to do API testing by providing many features such as API client to test API responses

Requestly API Client:

To show you a demo we will be again using Github Api

for this demo we will use this API: POST https://api.github.com/user/repos

this is POST request which will help to create repository for this you need to create Token from github with permission to create repository.

Now, we will use Requestly API client to make a request.

In Request Headers pass the AUTH_TOKEN so that Github servers can verify authenticity.

and add the JSON body like this

If you hit the Send Button.

You will get the Response body like this

and on Github Repositories you will find this Repo.

Mock Server:

You can Mock any api using Requestly Mock Server feature.

To demonstrate this we will mock this Github https://api.github.com/users/Arunshaik2001 api.

Click on Create New Mock API button make sure to login on Requestly.

I have changes the login value from Arunshaik2001 to Arunshaik21.

Now, click Save and then click Test.

Now mock api has been created you can use this to mock response.

There are many other Requestly features that will help you in testing APIs which are explained in detail in other articles. If you want to modify the API request body to modify request body on the fly you can use HTTP rules and modify the API response body you can modify any API/HTML/CSS/JS scripts. You can also import/export http sessions using Requestly.


It is important to know the components included in an API which will help in testing various aspects of the API and to ease the process developer can use open-source Requestly app which provides various features to understand about an API and do testing easily without any hastle.

This article was written by:

Dinesh Thakur

Dinesh Thakur

Dinesh Thakur, a computer science student with a profound love for programming, has been fascinated by technology's problem-solving capabilities since a young age. His dedication to programming has only deepened with time, as he spends numerous hours mastering new languages, frameworks, and tools. Whether working on personal projects or contributing to team endeavors, he consistently approaches new challenges with enthusiasm, building innovative solutions along the way.

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