What are HTTP Headers?

By onjsdev

Apr 1st, 2024

An HTTP request consists of two parts: the body and the header. While the body contains data transferred to the server, the header contains essential information and instructions that guide the behavior of web browsers, servers, and other web applications.

In this article, we'll explore the fundamentals of HTTP headers, their types, and their significance in web development.

What are HTTP Headers?

HTTP headers are metadata elements transmitted between the client (e.g., a web browser or mobile application) and the server during an HTTP (Hypertext Transfer Protocol) request-response cycle. These headers provide additional information about the request or response.

Anatomy of an HTTP Header

An HTTP header consists of a case-insensitive name followed by a colon and a space, then the header value. Headers are typically included in the request and response messages exchanged between the client and server. Here's a basic example:

HeaderName: HeaderValue

For example,

Content-Type: application/json

In this example, the Content-Type header indicates that the content being sent or received is in JSON format.

Types of HTTP Headers

HTTP headers can be categorized into two main types: request headers and response headers.

Request Headers

Request headers convey information about the client's request and preferences. Some common request headers include:

  • User-Agent: Identifies the user agent (browser or other client) initiating the request.
  • Accept: Informs the server about the types of media that the client can process.
  • Authorization: Provides credentials for accessing protected resources.

Response Headers

Response headers, on the other hand, provide information about the server's response and additional instructions for the client. Examples of response headers include:

  • Content-Type: Specifies the media type of the resource sent to the client.
  • Cache-Control: Directs how caching should be performed.
  • Server: Identifies information about the software used by the origin server.

Importance of HTTP Headers

It is important to set correct HTTP headers during the process of the HTTP requests as they serve various critical purposes, including:

  • Content Negotiation: The Accept header in the request allows clients to specify the type of content they can process, enabling servers to respond accordingly.
  • Security: Headers like Strict-Transport-Security and Content-Security-Policy enhance the security of web applications by enforcing specific policies.
  • Caching: Headers like Cache-Control and Expires control how browsers cache and revalidate resources.
  • Authentication: The Authorization header is crucial for accessing protected resources

HTTP Headers vs HTTP Body

You may think that both HTTP headers and bodies contain some information and wonder what differences between them are.

Let's briefly take a look at this:

As outlined above, the HTTP header contains metadata and instructions about the HTTP message, while the body contains the actual data being transmitted.

The content of the body depends on the nature of the HTTP message:

Request Body:

  • In POST requests, the body often contains data to be submitted to the server (e.g., form data or JSON payload).
  • In GET requests, the body is typically empty, as parameters are included in the URL. Response Body:

Response body,

  • The body carries the requested resource, which could be HTML content, JSON data, images, or any other media type.


In summary, HTTP headers are important part of the World Wide Web, allowing metadata about HTTP requests and responses to be sent during the transmission.

Thank you for reading