CSP: prefetch-src

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The HTTP Content-Security-Policy (CSP) prefetch-src directive specifies valid resources that may be prefetched or prerendered.

CSP version 3
Directive type Fetch directive
default-src fallback Yes. If this directive is absent, the user agent will look for the default-src directive.

Syntax

One or more sources can be allowed for the prefetch-src policy:

Content-Security-Policy: prefetch-src <source>;
Content-Security-Policy: prefetch-src <source> <source>;

Sources

<source> can be any one of the values listed in CSP Source Values.

Note that this same set of values can be used in all fetch directives (and a number of other directives).

Example

Prefetch resources do not match header

Given a page with the following Content Security Policy:

Content-Security-Policy: prefetch-src https://example.com/

Fetches for the following code will return network errors, as the URLs provided do not match prefetch-src's source list:

    <link rel="prefetch" src="https://example.org/"></link>
    <link rel="prerender" src="https://example.org/"></link>

Specifications

Specification
Content Security Policy Level 3
# directive-prefetch-src

Browser compatibility

BCD tables only load in the browser

See also