What is Robots.txt
Robots.txt is a text file webmasters create to instruct web robots (typically search engine robots) how to crawl pages on their website. The robots.txt file is part of the the robots exclusion protocol (REP), a group of web standards that regulate how robots crawl the web, access and index content, and serve that content up to users. The REP also includes directives like meta robots, as well as page-, subdirectory-, or site-wide instructions for how search engines should treat links (such as “follow” or “nofollow”).
User-agent: [user-agent name]
Disallow: [URL string not to be crawled]
How does robots.txt work?
Search engines have two main jobs:
Crawling the web to discover content;
Indexing that content so that it can be served up to searchers who are looking for information.
To crawl sites, search engines follow links to get from one site to another — ultimately, crawling across many billions of links and websites. This crawling behavior is sometimes known as “spidering.”
After arriving at a website but before spidering it, the search crawler will look for a robots.txt file. If it finds one, the crawler will read that file first before continuing through the page. Because the robots.txt file contains information about how the search engine should crawl, the information found there will instruct further crawler action on this particular site. If the robots.txt file does not contain any directives that disallow a user-agent’s activity (or if the site doesn’t have a robots.txt file), it will proceed to crawl other information on the site.
Technical robots.txt syntax
Robots.txt syntax can be thought of as the “language” of robots.txt files. There are five common terms you’re likely come across in a robots file. They include:
User-agent: The specific web crawler to which you’re giving crawl instructions (usually a search engine). A list of most user agents can be found here.
Disallow: The command used to tell a user-agent not to crawl particular URL. Only one “Disallow:” line is allowed for each URL.
Allow (Only applicable for Googlebot): The command to tell Googlebot it can access a page or subfolder even though its parent page or subfolder may be disallowed.
Crawl-delay: How many seconds a crawler should wait before loading and crawling page content. Note that Googlebot does not acknowledge this command, but crawl rate can be set in Google Search Console.
Sitemap: Used to call out the location of any XML sitemap(s) associated with this URL. Note this command is only supported by Google, Ask, Bing, and Yahoo.