What is the Ajax crawling scheme specification?

The Ajax crawling scheme is an old specification that describes how to make any Ajax websites crawlable by Google and some other bots. This specification defines a protocol between bots and HTTP servers. This protocol allows bots to retrieve HTML snapshots instead of the HTML pages sent to regular users and requiring JavaScript to be properly rendered.

The Ajax crawling scheme specification has been officially deprecated and has been replaced with the Dynamic Rendering recommendation.