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http header

Content-Security-Policy-Report-Only header

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The HTTP Content-Security-Policy-Report-Only response header helps to monitor Content Security Policy (CSP) violations and their effects without enforcing the security policies. This header allows you to test or repair violations before a specific Content-Security-Policy is applied and enforced.

The CSP report-to directive must be specified for reports to be sent: if not, the operation won’t have any effect.

Violations of the policy may be reported using the Reporting API. Reports can be observed in the page for which the policy is being enforced, using a ReportingObserver, and sent to server endpoints defined in a Reporting-Endpoints HTTP response header and selected using the CSP report-to directive. For more information see CSPViolationReport.

For more information, see our Content Security Policy (CSP) guide.

[!NOTE] The header can also be used with the deprecated report-uri directive (this is being replaced by report-to). The usage and resulting report syntax is slightly different; see the report-uri topic for more details.

Header type [Response header](https://developer.mozilla.org/en-US/docs/Glossary/Response%20header)
This header is not supported inside a [``](/firefox/mdn/html/reference/elements/meta/) element.

Syntax

Content-Security-Policy-Report-Only: <policy-directive>; …; <policy-directive>; report-to <endpoint-name>

Directives

The Content-Security-Policy-Report-Only header supports all Content-Security-Policy directives except sandbox, which is ignored.

[!NOTE] The CSP report-to directive should be used with this header or it will have no effect.

Examples

Using Content-Security-Policy-Report-Only to send CSP reports

To use the report-to directive, you first need to define a corresponding endpoint using the Reporting-Endpoints response header. In the example below, we define a single endpoint named csp-endpoint.

Reporting-Endpoints: csp-endpoint="https://example.com/csp-reports"

We can then define the destination of the report using report-to and report-uri, as shown below. Note that this particular report would be triggered if the page loaded resources insecurely, or from inline code.

Content-Security-Policy-Report-Only: default-src https:;
  report-uri /csp-report-url/;
  report-to csp-endpoint;

[!NOTE] The report-to directive is preferred over the deprecated report-uri, but we declare both because report-to does not yet have full cross-browser support.

Specifications

SpecificationsStandards references are available on the canonical MDN page.

Browser compatibility

Browser compatibilityCompatibility data is available on the canonical MDN page.

See also