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Content-Security-Policy: prefetch-src directive

files/en-us/web/http/reference/headers/content-security-policy/prefetch-src/index.md

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{{Deprecated_Header}}{{Non-standard_header}}

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

<table class="properties"> <tbody> <tr> <th scope="row">CSP version</th> <td>3</td> </tr> <tr> <th scope="row">Directive type</th> <td>{{Glossary("Fetch directive")}}</td> </tr> <tr> <th scope="row">{{CSP("default-src")}} fallback</th> <td> Yes. If this directive is absent, the user agent will look for the <code>default-src</code> directive. </td> </tr> </tbody> </table>

Syntax

http
Content-Security-Policy: prefetch-src 'none';
Content-Security-Policy: prefetch-src <source-expression-list>;

This directive may have one of the following values:

  • 'none'
    • : No resources of this type may be loaded. The single quotes are mandatory.
  • <source-expression-list>
    • : A space-separated list of source expression values. Resources of this type may be loaded if they match any of the given source expressions. For this directive, the following source expression values are applicable:

Example

Prefetch resources do not match header

Given a page with the following Content Security Policy:

http
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:

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

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

  • {{HTTPHeader("Content-Security-Policy")}}