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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsHTTP_REFERER is the misspelled standard name of an HTTP request header that tells a server which URI context led to the current request. Depending on browser policy, it may contain the referring page’s origin, path and query string—or only the origin, or nothing at all. It is useful for analytics and diagnostics, but it is not a reliable identity credential or authorization proof.
What the HTTP Referer header means
The header field is spelled Referer, although “referrer” is the correct English spelling. It is defined as a request header: the user agent sends a URI reference for the resource from which the target URI was obtained. Servers commonly use it for traffic attribution, link diagnostics, logging, caching decisions and finding obsolete links.
The related response header is spelled Referrer-Policy. The different spellings are intentional standards terminology: use Referer when reading the request and Referrer-Policy when controlling what browsers disclose.
What information can be in Referer?
A Referer value can be a complete URL, an origin, or be absent. A complete value can include the scheme, host, port, path and query string. It cannot include a URL fragment (the part after #) or username/password information. Browsers can also truncate or omit information according to policy, privacy settings, redirects, extensions or intermediary behavior.
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For example, a request generated from https://shop.example/account/orders?customer=42 might include:
Referer: https://shop.example/account/orders?customer=42Under a stricter policy, the same cross-origin request could send only:
Referer: https://shop.examplePutting secrets, access tokens, personal data or confidential identifiers in URLs is therefore risky: a path or query string can be disclosed to another origin, logged by infrastructure or retained in analytics systems.
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How Referrer-Policy controls disclosure
Site operators normally set an HTTP response header:
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| Policy | Same-origin requests | Cross-origin requests | HTTPS page to HTTP destination |
|---|---|---|---|
no-referrer |
No Referer | No Referer | None |
same-origin |
Full URL | No Referer | No cross-origin Referer |
strict-origin |
Origin only | Origin only | None |
strict-origin-when-cross-origin |
Full URL | Origin only | None |
unsafe-url |
Full URL | Full URL | Full URL |
When no valid policy is supplied, MDN documents strict-origin-when-cross-origin as the browser default. That default preserves the full URL for same-origin navigation, but sends only the origin to another origin and suppresses the header when moving from HTTPS to HTTP.
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Choosing a policy
- Use
no-referrerwhen referral context is unnecessary and maximum suppression is preferred. - Use
same-originwhen internal analytics need full URLs but external sites should receive nothing. - Use
strict-originwhen destinations need origin-level attribution without paths or queries. - Use
strict-origin-when-cross-originwhen you want the modern default balance between internal diagnostics and cross-origin privacy. - Avoid
unsafe-urlunless full cross-origin URL disclosure is an explicit, understood requirement; it can expose private URL data to insecure destinations.
Browser and protocol safeguards
Under RFC 9110 §10.1.3, a user agent must not include fragments or userinfo in Referer. It must not send the header in an unsecured HTTP request when the referring resource was accessed securely. These rules limit accidental disclosure, but they do not make URL paths and query strings private.
Requests may also lack Referer because a user navigated directly, a policy suppressed it, a privacy feature removed it, a redirect changed the context, or an intermediary deleted it. Conversely, the value is context supplied by a client and should not be treated as proof that a navigation actually occurred.
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No—not by itself. Do not use a present Referer as the sole authorization check, and do not treat its absence as proof of a malicious request. RFC 9110 notes that some sites use the field in CSRF defenses, but intermediaries can remove it and legitimate requests can omit it.
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CSRF protection
Use an established CSRF defense such as a server-validated anti-CSRF token, with appropriate cookie settings such as SameSite. Referer (and, where applicable, the related Origin request header) can be supplementary signals, but a missing value must not break legitimate clients unless your threat model and fallback behavior have been carefully designed.
Access control and authentication
Enforce permissions with authenticated sessions, access tokens and server-side authorization. A Referer value does not establish who made the request, what they are allowed to access, or whether the value was preserved unchanged across proxies.
Practical configuration examples
HTTP response header
HTTP/1.1 200 OK
Referrer-Policy: strict-origin-when-cross-origin
Content-Type: text/htmlHTML document fallback
<meta name="referrer" content="strict-origin-when-cross-origin">Per-element control
<a href="https://partner.example/report"
referrerpolicy="no-referrer">Open report</a>Apply the broad policy at the HTTP layer, then use a more restrictive element-level setting for links, images, frames or requests that need additional privacy.
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How to interpret a Referer value safely
- Parse it as untrusted input and validate its syntax before logging or displaying it.
- Expect it to be missing, shortened to an origin, or altered by browser and network privacy controls.
- When matching an internal source, compare a normalized scheme, host and port rather than trusting arbitrary text.
- Never echo the value into HTML, scripts or headers without context-appropriate output encoding.
- Remove or protect sensitive query parameters in your own URLs, since policy cannot guarantee that every client or intermediary will suppress them.
Common misunderstandings
“Referer always contains the previous page.”
It may be absent, reduced to an origin, or removed in transit. A direct visit has no referring page to report.
“The header is called Referrer.”
The request field’s standardized spelling is Referer. Referrer-Policy is the correctly spelled control header.
“A full Referer proves the request came from my site.”
It is only client-supplied context and is not an authorization credential. Use server-side authentication and authorization instead.
“HTTPS prevents URL leakage.”
HTTPS protects transport between the browser and an HTTPS server, but a page’s path or query can still be sent to another origin when policy permits it and can be recorded by the receiving server.
The Bottom Line
Use Referer as optional context for analytics and troubleshooting, control it with a deliberate Referrer-Policy, keep secrets out of URLs, and never rely on it alone for CSRF defense, authentication or access control.
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