What is a Referer header?
The address of the page that linked to the resource being requested.
Referer (the famously misspelled header) tells a website which page a visitor clicked through from, which is how analytics tools attribute traffic and how some sites implement basic hotlink protection for images or downloads. Browsers increasingly strip or truncate it by default for privacy, so a website that leans on Referer for security decisions rather than just analytics is standing on increasingly shaky ground.
Common use case
An analytics platform reads Referer to attribute a visit to the search engine, social post, or external site that linked to the page.
Example
Referer: https://www.google.com/History
Part of the original HTTP/1.0 specification, RFC 1945 (1996).
Did you know?
The header name is a permanent, deliberately preserved misspelling of "referrer" - a typo made by an early HTTP spec author that shipped into the standard and has been technically impossible to fix ever since without breaking the entire web.