PHI is a free Chrome extension developed by mike.chen. It falls under the category of Browsers and specifically the subcategory of Add-ons & Tools. PHI stands for Page Header Info and its main purpose is to display a list of header information for all tag pages.

With PHI, users can easily view important header information for any webpage they visit. The extension provides details such as og-title, og-type, og-url, og-image, og-site_name, description, canonical, robots, twitter-card, and twitter-site. This information can be useful for web developers, SEO specialists, or anyone interested in understanding the metadata of a webpage.

PHI offers a simple and straightforward interface, making it easy to access and view the header information. Whether you're analyzing websites for SEO purposes or simply curious about the metadata of a page, PHI is a handy tool to have in your browser.

Please note that PHI is available only for the Chrome browser, and it is completely free to use.