Integrity-Policy-Report-Only header

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).

Reports may be generated for requests on specified request destinations that omit integrity metadata, or that are made in no-cors mode. For reports to be sent to a reporting endpoint, the Integrity-Policy-Report-Only header must specify a valid reporting endpoint name that matches an endpoint declared using the Reporting-Endpoints header. Reports are generated using the Reporting API, and may also be observed in the page for which the integrity policy is being reported, using a ReportingObserver. The format of the report body is given by the IntegrityViolationReportBody dictionary (a JSON-serialized form of this body is sent in POSTs to reporting server endpoints).

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

Header type	Response header
Forbidden request header	no

Syntax

http

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.

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 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.

http

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.

json

{
  "type": "integrity-violation",
  "url": "https://example.com",
  "body": {
    "documentURL": "https://example.com",
    "blockedURL": "https://example.com/main.js",
    "destination": "script",
    "reportOnly": false
  }
}

Specifications

Specification
Subresource Integrity # integrity-policy-section