The HTTP Integrity-Policy-Report-Only response header allows website administrators to report on resources that the user agent loads that would violate Subresource Integrity guarantees if the integrity policy was enforced (using the Integrity-Policy header).

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 endpoints field. For more information see IntegrityViolationReport.

The header allows developers to test integrity policies and fix any content issues before eventually deploying an Integrity-Policy header to enforce the policy.

Syntax

Integrity-Policy-Report-Only: blocked-destinations=(<destination>),sources=(<source>),endpoints=(<endpoint>)

The header values are defined as structured field dictionaries with the following keys:

blocked-destinations

A list of request destinations that must include valid integrity metadata. Allowed values are:

script

Script resources.

style

Stylesheet resources.

sources Optional

A list of integrity sources that must include integrity metadata. Allowed values are:

inline

The integrity metadata source is inline to the content, such as the integrity attribute. This is the default.

As this is the default and only value, omitting sources is equivalent to specifying sources=(inline).

endpoints Optional

A list of reporting endpoint names that indicate where reports will be sent. The reporting endpoints must be defined in a Reporting-Endpoints header.

Examples

Reporting when scripts lack integrity metadata

This example shows a document that reports to a server endpoint when any <script> (or HTMLScriptElement) does not specify an integrity attribute, or when a script resource is requested in no-cors mode.

Note that the integrity-endpoint used in Integrity-Policy-Report-Only is defined in the Reporting-Endpoints header.

Reporting-Endpoints: integrity-endpoint=https://example.com/integrity, backup-integrity-endpoint=https://report-provider.example/integrity
Integrity-Policy-Report-Only: blocked-destinations=(script), endpoints=(integrity-endpoint backup-integrity-endpoint)

The report payload might look like this. Note that the body.reportOnly property is true, because this report was triggered by a violation of Integrity-Policy-Report-Only.

{
  "age": "176279",
  "type": "integrity-violation",
  "url": "https://example.com",
  "body": {
    "documentURL": "https://example.com",
    "blockedURL": "https://example.com/main.js",
    "destination": "script",
    "reportOnly": "true"
  },
  "user_agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/145.0.0.0 Safari/537.36"
}

Specifications

Browser compatibility

See also

• Integrity-Policy
• Reporting-Endpoints
• ReportingObserver
• IntegrityViolationReport
• Integrity Policy in Subresource Integrity
• Reporting API