Use HTTP "Accept" header for mobile markup language
Request headers from Google's feature-phone mobile crawl will always use the HTTP "Accept" header to explicitly tell your site that it should return documents with mobile content types, if available, rather than standard HTML. If your site respects this standard, your site will return feature-phone mobile content correctly to our mobile crawl.
In some cases,
Accept headers are ambiguous. For example,
text/html is the content type for both cHTML, which is appropriate for certain types of mobile devices, and HTML, which is generally intended for desktop computers. Google's feature-phone mobile crawl does its best to appear to be a mobile device, so if your site tries to detect mobile devices in other ways in a case like this, it will probably work for Google's feature-phone mobile crawl as well.
Google's feature-phone mobile crawl will send a user-agent header that contains the string "Googlebot-Mobile".
For more information, please see our mobile Webmaster Guidelines.