Referrer-Policy is an HTTP response header that controls how much referrer information the browser includes when a user navigates from the current page to another page. It allows site owners to balance privacy concerns with the need for referrer data in analytics and security contexts.
The header supports several values ranging from no-referrer (never send referrer information) to unsafe-url (always send the full URL). The most commonly recommended value is strict-origin-when-cross-origin, which sends the full URL for same-origin requests but only the origin (domain) for cross-origin requests, and sends nothing when downgrading from HTTPS to HTTP. Web privacy books on Amazon explain the options.
For URL shortening services, Referrer-Policy affects how much information about the referring page is available when a user clicks a short URL. If the referring page sets a restrictive policy, the shortening service may not receive the full referrer URL, limiting the analytics data available to link owners.
The interaction between Referrer-Policy and URL shortening analytics is an important consideration. Services that rely on referrer data for traffic source analysis should be aware that an increasing number of sites and browsers restrict referrer information by default. Web security configuration books on Amazon discuss header configuration.