A robots.txt file tells search engine crawlers which URLs the crawler can access on your site. This is used mainly to avoid overloading your site with requests; it is not a mechanism for keeping a web page out of Google.

The Robots Exclusion Standard was quickly embraced by the web community. Most major search engine crawlers adopted it, respecting the rules outlined in robots. txt files. While it's a voluntary protocol (bad bots can ignore it), the vast majority of web crawlers still abide by it.