GET, POST, and safely surfacing more of the web

Tuesday, November 01, 2011

As the web evolves, Google's crawling and indexing capabilities also need to progress. We improved our indexing of Flash, built a more robust infrastructure called Caffeine, and we even started crawling forms where it makes sense. Now, especially with the growing popularity of JavaScript and, with it, AJAX, we're finding more web pages requiring POST requests—either for the entire content of the page or because the pages are missing information and/or look completely broken without the resources returned from POST. For Google Search this is less than ideal, because when we're not properly discovering and indexing content, searchers may not have access to the most comprehensive and relevant results.

We generally advise to use GET for fetching resources a page needs, and this is by far our preferred method of crawling. We've started experiments to rewrite POST requests to GET, and while this remains a valid strategy in some cases, often the contents returned by a web server for GET vs. POST are completely different. Additionally, there are legitimate reasons to use POST (for example, you can attach more data to a POST request than a GET). So, while GET requests remain far more common, to surface more content on the web, Googlebot may now perform POST requests when we believe it's safe and appropriate.

We take precautions to avoid performing any task on a site that could result in executing an unintended user action. Our POST requests are primarily for crawling resources that a page requests automatically, mimicking what a typical user would see when they open the URL in their browser. This will evolve over time as we find better heuristics, but that's our current approach.

Let's run through a few POST request scenarios that demonstrate how we're improving our crawling and indexing to evolve with the web.

Examples of Googlebot's POST requests

  • Crawling a page via a POST redirect
          <body onload=";">
            <form name="foo" action="request.php" method=