What is a web sniffer? It's an online tool to view HTTP request and response headers. HTTP header is a part of response sent by a server with a requested page. It includes information like response code (200 success, 301/302 redirect etc.), content type, server identifier, last modification time and other details. This online HTTP/HTTPS header checker lets you see the HTTP headers for any given URL.
How to use web sniffer? It's very simple and completely free, just type a website URL or a server's IP address in the URL text field and press submit. The URL sniffer will follow the URL and check website headers. WebSniffer will then output the HTTP request header, HTTP response header including the HTTP status code and will also show you the content of the requested page.