Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

Note: Public Key Pinning mechanism was deprecated in favor of Certificate Transparency and Expect-CT header.

The HTTP Public-Key-Pins-Report-Only response header was used to send reports of pinning violation to the report-uri specified in the header but, unlike Public-Key-Pins still allows browsers to connect to the server if the pinning is violated. The header is silently ignored in modern browsers as support for HPKP has been removed. Use Certificate Transparency and the Expect-CT header instead.

For more information, see the Public-Key-Pins header reference page and the HTTP Public Key Pinning article.

Header type Response header
Forbidden header name no


Public-Key-Pins-Report-Only: pin-sha256="<pin-value>";



The quoted string is the Base64 encoded Subject Public Key Information (SPKI) fingerprint. It is possible to specify multiple pins for different public keys. Some browsers might allow other hashing algorithms than SHA-256 in the future.


This directive is meaningless for the Public-Key-Pins-Report-Only header, it will be ignored by user agents and the header will not be cached.

includeSubDomains Optional

If this optional parameter is specified, this rule applies to all of the site's subdomains as well.


Pin validation failures are reported to the given URL. This directive should be used with this header; otherwise, this header will be a no-op.



In this example, pin-sha256="cUPcTAZWKaASuYWhhneDttWpY3oBAkE3h2+soZS7sWs=" pins the server's public key used in production. The second pin declaration pin-sha256="M8HztCzM3elUxkcjR2S5P4hhyBNf6lHkmjAHKhpGPWE=" also pins the backup key. This key pinning is also valid for all subdomains, which is told by the includeSubDomains declaration. Finally, report-uri="" explains where to report pin validation failures.


Public Key Pinning Extension for HTTP
# section-2.1

Browser compatibility

BCD tables only load in the browser

See also