X-DNS-Prefetch-Control

ResponseActive

X-DNS-Prefetch-Control controls whether the browser proactively resolves DNS for links on the page. Browsers prefetch DNS for links in anchor tags to reduce latency when a user clicks. 'on' enables prefetching (default for HTTP pages), 'off' disables it. HTTPS pages disable DNS prefetch by default for privacy – this header can re-enable it.

X-DNS-Prefetch-Control: on | off

Description

Browsers resolve the hostnames of links visible in the page before the user clicks them, reducing the DNS lookup latency from the click. This is beneficial for performance but leaks browsing intent to DNS resolvers. HTTPS pages disable this by default. DNS prefetching can be re-enabled with X-DNS-Prefetch-Control: on, or specific domains can be prefetched with <link rel=dns-prefetch href=//cdn.example.com>.

Examples

Enable prefetch

http

X-DNS-Prefetch-Control: on

Disable (privacy)

http

X-DNS-Prefetch-Control: off

Inline hint

http

<!-- In HTML head: -->
<link rel="dns-prefetch" href="//api.example.com">

Specification

Non-standard – X-DNS-Prefetch-Control specification →