For some sites Google will show an added feature in the search results – a sitelinks search box, so that searchers can do a secondary search just for results on your own site.  But not all sites show the search box, which appears to be linked to both site quality and searcher intent – if a searcher is likely to search for results just from your site, Google is more likely to add the search box to your result.

Google actually shows two different types of sitelinks search boxes.  One is simply a site:example.com search for your site, such as for Wikipedia – note it says “Results from Wikipedia.org” and the search results are merely a second Google search.

The second, which requires schema, will allow Google to show the results on your own site, using your site’s own search engine instead. Walmart uses the schema so their search box will instead show the results on Walmart’s own site.  Note the slight change of text in the search box to “Search walmart.com” instead.

For many sites, hosting your own search results for this makes much more sense for many reasons – page views and ad revenue are two big ones.  So for these reasons, adding schema makes a lot of sense – it just requires schema added to the homepage.

If you do not already show a Google search box in your Google search results listing, merely adding the schema won’t trigger Google to suddenly display it.  So while you can still add the schema, don’t expect to suddenly see the site search box for your site in the search results.  This is something that John Mueller explained in a recent Google Webmaster Office Hours.

The thing to keep in mind with the sitelinks search box is that we don’t show it just because you have the markup, but rather with the markup, we are able to show the version that you prefer.

So if we don’t show any sitelinks search box for your site for queries for your site, then adding that markup isn’t going to change anything, isn’t going to encourage us to start showing that.  But if we are already showing a sitelinks search box and we’re linking to a site: query for your site, and you say well I prefer people to within my own site because I have a better search results internally or maybe I can place some more marketing material around the search results or maybe an ad or something, then that’s something you can do.

Once we’re showing the sitelinks search box, that markup helps us pick the version that you prefer to have shown.

So adding schema to use your own internal search engine from the Google search results will work great if Google is already showing your sitelinks search box in their search results.  But don’t expect it to magically appear in the search results simply because you added the markup.