WhatWeb is an open-source reconnaissance tool used for web scanning and fingerprinting. It is designed to identify and gather information about the technologies and frameworks used by a target website. WhatWeb is capable of detecting various aspects of a website, including web servers, content management systems (CMS), programming languages, JavaScript frameworks, and more. 

it sends HTTP requests with different headers and analyzes the responses to identify patterns and signatures. This allows WhatWeb to make educated guesses about the technologies employed by the website. 

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