Get HTTP Headers

Ever wondered what information your browser sends to website servers when you load a page? All that data is contained in HTTP headers; you can view them with a simple browser extension. Check out our guide to see what all those headers mean.

Introduction

In computing, HTTP headers are components of the message header of requests and responses in the Hypertext Transfer Protocol (HTTP). They define the operating parameters of an HTTP transaction.

HTTP headers allow the client and the server to pass additional information with the request or the response. A requesting client, for example, can use HTTP headers to specify the preferred content type or compression method.

What are HTTP headers?

HTTP headers are the backbone of the internet as we know it. They are sent with every request, whether it's a GET request for a webpage or a POST request sending data to a server.

HTTP headers let the client and server communicate important information about the request and response. For example, they can be used to indicate the content type of the data being sent, whether the data has been compressed, and how long the response will take.

In addition to request and response headers, there are also general headers that apply to both. These include headers for caching, authentication, and Cookies.

How to view HTTP headers

You can use a web development tool like Firefox’s Web Developer extension to view HTTP headers. This is useful for seeing what information is being sent back and forth between your browser and a web server and can be used to debug problems with websites.

To view HTTP headers in Firefox:

1. Install the Web Developer extension.
2. Open the web page you want to inspect in Firefox.
3. Click the Web Developer icon in the toolbar, then click “Web Console”.
4. In the Web Console, click the “Network” tab.
5. Reload the page you want to inspect.
6. Click on the page in the list of loaded resources to select it, then click the “Headers” tab at the bottom of the pane.
7. The HTTP headers will be displayed in this pane.

What information do HTTP headers contain?

HTTP headers are name-value pairs returned in responses from a Web server. They include information about the server, the answer, and the client. Each header is separated by a carriage return and line feed character sequence (CRLF).

The headers can be divided into two categories: general headers and request headers. Available headers apply to requests and responses, while request headers apply only to requests. The most common titles are listed below:

General Headers:
Cache-Control – This header is used to control caching of the response by the client.
Connection – This header indicates whether persistent links should be used.
Date – This header indicates the date and time the message was sent.
Pragma – This header implements various directives for backward compatibility with HTTP/1.0 caches.
Trailer – This header is used in chunked transfer encoding to indicate which message headers will be present in each chunked response body.
Transfer-Encoding – This header indicates what type of encoding has been used on the body of the message.
Upgrade – This header is used to indicate that the client would like to upgrade to a different protocol, such as HTTP/2.0 or WebSockets.
Via – This header is used to specify proxies that have forwarded the message.
Warning – This header indicates any special conditions relating to the message.

Request Headers: Response Headers: Entity Headers: General Request Response All Cache-Control ETag Allow Connection Expires Content-Encoding Date Content-Language Trailer Pragma Transfer-Encoding Upgrade Upgrade-Insecure-Requests Via Warning Accept Age Accept-Charset Proxy-Authenticate Accept-Encoding Public Accept-Language Retry-After Authorization Server Cookie Vary Expect WWW-Authenticate If-Match Connection If-None-'Match Content-'Encoding If-'Modified-'Since Content-'Language If-'Range

How do HTTP headers affect web browsing?

When you type a URL into your web browser and hit enter, your computer sends an HTTP request to the website's server. The request includes headers that provide information about the browser and the request itself. The server uses this information to determine how to respond, and it sends its response back to the browser in the form of HTTP headers.

Headers can affect many aspects of web browsing, including security, privacy, performance, and compatibility. For example, some headers can be used to enable or disable features like cookies and JavaScript. Others can be used to control how content is cached or compressed. And still, others can be used to indicate preferred content languages or character encodings.

While most headers are optional, a few are required in all HTTP requests and responses. These include the "Host" header, which specifies the domain name of the server being contacted; the "Date" header, which indicates the date and time at which the message was generated; and the "Content-Length" header, which gives the size of the message body in bytes.

Privacy and security implications of HTTP headers

HTTP headers send information about the client (e.g., the browser) and the server (e.g., the website) to each other. This information can include things like the type of browser being used, the IP address of the client, and cookies.

Some HTTP headers can have privacy and security implications for users if they are not correctly configured. For example, the "Cookie" header can be used to track users as they browse the web if cookies are not correctly configured. The "Referer" header can also leak sensitive information, such as the URL of the page that was visited before the current page, if it is not configured correctly.

Therefore, it is important to know the potential privacy and security implications of HTTP headers when configuring your web browser or server.

Conclusion

We’ve seen how to use the get all headers function to return all the headers sent by the client and how to use the header function to set headers to be sent back to the client. We’ve also seen how to send a raw HTTP header.