By Shad Super in Questions —

What Are the Differences in robots.txt Directives Supported by Major Search Engines Like Google, Bing, and Yahoo, and How Can I Cater to All?

Summary

Search engines like Google, Bing, and Yahoo have specific guidelines and supported directives for the robots.txt file, which webmasters use to control crawler access to their sites. While there are common directives supported by all major search engines, some directives are specific to only one or a few engines. To ensure compatibility, it's essential to understand these nuances and create a comprehensive robots.txt file.

Overview of robots.txt Directives

The robots.txt file is a simple text file located at the root of a website, which provides instructions to web crawlers about which pages or sections to crawl or not to crawl. Here's a look at commonly used directives:

  • User-agent: Specifies the web crawler to which the rules apply.
  • Disallow: Blocks crawlers from accessing specified pages or directories.
  • Allow: Overrides a Disallow directive to permit access to specific pages or directories.
  • Sitemap: Provides the location of the website's sitemap to help guide crawlers.

Supported Directives by Major Search Engines

While the core directives like User-agent, Disallow, and Allow are universally supported, there are some directives and features unique to specific search engines:

Google

Google supports all the common directives and has additional proprietary directives:

  • Crawl-delay: Google does not support this directive. Instead, it manages crawl rate through Google Search Console.
  • Noindex: Previously recognized but deprecated; Google now recommends using the <meta> tag in the HTML instead.
  • Sitemap: Google supports listing sitemaps in the robots.txt file.

For more details, refer to Google’s Guide on robots.txt.

Bing

Bing also supports the standard directives and offers additional features:

  • Crawl-delay: Supported by Bing to control the crawl rate.
  • Sitemap: Bing supports the sitemap directive.

For more information, see Bing’s robots.txt Documentation.

Yahoo

Yahoo’s search technology is powered by Bing, so it adheres to the same guidelines:

  • Crawl-delay: Supported by Yahoo (via Bing).
  • Sitemap: Supported by Yahoo (via Bing).

Refer to Yahoo's policy through the Bing documentation.

Best Practices to Cater to All Search Engines

To ensure your robots.txt file works effectively across all major search engines, follow these best practices:

Universal Compatibility

  • Use the User-agent directive to specify rules for different crawlers.
  • Apply the Disallow directive to block access where needed.
  • Utilize the Allow directive to permit access to specific content within a disallowed directory.

Handling Crawl Delay

If you need to manage crawl rates:

  • Use the Crawl-delay directive for Bing and Yahoo.
  • For Google, use Google Search Console to set crawl rate preferences.

Sitemaps

Ensure you include the Sitemap directive pointing to your XML sitemaps:

Sitemap: https://www.yourwebsite.com/sitemap.xml

Sample robots.txt File

User-agent: *
Disallow: /private/
Allow: /private/public-page.html

User-agent: Googlebot
Disallow: /no-google/

User-agent: Bingbot
Crawl-delay: 10

Conclusion

By understanding the directives supported by each major search engine and standardizing your robots.txt file accordingly, you can effectively manage crawler access to your site content. Be sure to regularly review and update your robots.txt file to accommodate changes in indexing guidelines and your site's structure.

References