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

The Speculation-Rules response header provides one or more URLs pointing to text resources containing speculation rule JSON definitions. When the response is an HTML document, these rules will be added to the document's speculation rule set. See the Speculation Rules API for more information.

The resource file containing the speculation rules JSON can have any valid name and extension, but it must be served with an application/speculationrules+json MIME type.

Note: This mechanism provides an alternative to specifying the JSON definition inside an inline <script type="speculationrules"> element. Specifying an HTTP header is useful in cases where developers are not able to directly modify the document itself.

Header type Response header
Forbidden header name no


Speculation-Rules: <url-list>



A comma-separated list of URLs pointing to text resources containing speculation rule JSON definitions. The JSON contained in the text files must follow the same rules as that contained inside inline <script type="speculationrules"> elements. See Speculation rules JSON representation for the syntax reference.


Single speculation rules file reference:

Speculation-Rules: "/rules/prefetch.json"

Multiple speculation rules file references:

Speculation-Rules: "/rules/prefetch.json","/rules/prerender.json"

Note: The URL values must be contained in quotes.


Speculation Rules
# speculation-rules-header

Browser compatibility

BCD tables only load in the browser

See also