The internet works based on HyperText Transfer Protocol or shortly called HTTP. This is a client server mechanism in which a client browser requests for a resource located on a web server. The web server will return a HTTP response whenever a browser requests a webpage. The response contains header data having useful information like a three digit HTTP status code. You can use the HTTP header data for various troubleshooting purposes like to check whether a webpage is available online.

You can enter any URL and find the response header data using this HTTP Header Checker tool. Simply enter the complete URL of a webpage and press "Submit" button to get the details.

Below are some of the important information you can find in the HTTP header response.

• Status code
• Redirection
• Server details
• Cache control headers
• Last modified date

For each request from the browser, server will send a three digit HTTP status code to indicate the status of the request. Generally you need the server response code to understand the result of the request. For example, status code 200 indicates everything is fine and the server returned the requested page successfully. HTTP status codes are classified into the following five categories based on the meaning:

• 1xx series indicating the code is only for informational purpose. For example, code 101 indicates the server switched the protocol according to browser's request.
• 2xx series indicating the communication is successful. For example, code 200 indicates a OK or successful communication.
• 3xx series indicating the requested resource is redirected to another page. For example, code 301 indicates a permanent redirection.
• 4xx series indicating an error in client request, for example code 404 indicates a requested page not found.
• 5xx series indicating an error in server response, for example code 500 indicates internal server error. 

Redirection is a useful information for troubleshooting purposes. It indicates the web page was moved to another place on the server. For example, when you check our domain webnots.com, you will see 301 - permanently redirected. This is because, the domain will redirect to https://www.webnots.com/. You will also see the new destination page URL along with status code 200 - OK.

When your site is not accessible, you can use this HTTP header checker tool to find the server response code and take necessary action. For example, status code 404 indicates that the page is not available. Probably, you might have wrongly deleted the page or modified the URL without setting up proper 301 redirect.

HTTP server response will show you the following server related details:

• Type of web server like Nginx or Apache.
• Connection type details like keep-alive.
• Cache-control type
• Supported HTTP version like HTTP/1.1

You can also find few other details like last modified date of the page, host-header and vary header. The last modified date is one of the useful parameter indicating when the page was last updated.