referers

Referers, in the context of the web, refers to the HTTP header field that informs a server about the address of the page from which a request originated. When a user clicks a link or submits a form, the browser typically sends a Referer header containing the URL of the referring page. This information helps servers perform analytics, tracing traffic sources, and supporting certain web features. The header is optional and may be omitted or altered by browsers, proxies, or privacy tools.

The header name is Referer due to an original misspelling in early HTTP specifications. Because of this history, many discussions refer to it as the “referrer” header in plain English, while the formal field name remains Referer.

Uses and limitations: Web analytics systems use the Referer header to attribute visits to source pages and campaigns, and to inform content recommendations. It can influence caching decisions and cross-site behavior. However, it is not reliable for security-critical decisions: the header can be missing, stripped, or rewritten during cross-origin requests, cache hops, or when privacy protections are active. Relying on it for authentication or authorization is not appropriate.

Privacy and policy: Users and organizations may restrict referer leakage to protect sensitive URLs or query parameters. The Referrer-Policy header allows controlling how much referer information is sent, with values such as no-referrer, origin, origin-when-cross-origin, and strict-origin. Browsers may also offer settings to suppress or modify referer data. Site operators often implement server-side analytics that do not depend solely on the referer header to balance usefulness with privacy.