Google has proposed an official internet standard for the rules included in robots.txt files.
Those rules, outlined in the Robots Exclusion Protocol (REP), have been an unofficial standard for the past 25 years.
While the REP has been adopted by search engines it’s still not official, which means it’s open to interpretation by developers. Further, it has never been updated to cover today’s use cases.
It's been 25 years, and the Robots Exclusion Protocol never became an official standard. While it was adopted by all major search engines, it didn't cover everything: does a 500 HTTP status code mean that the crawler can crawl anything or nothing? 😕 pic.twitter.com/imqoVQW92V
— Google Webmasters (@googlewmc) July 1, 2019
As Google says, this creates a challenge for website owners because the ambiguously written, de-facto standard made it difficult to write the rules correctly.
To eliminate this challenge, Google has documented how the REP is used on the modern web and submitted it to the Internet Engineering Task Force (IETF) for review.
Google explains what is included in the draft:
“The proposed REP draft reflects over 20 years of real world experience of relying on robots.txt rules, used both by Googlebot and other major crawlers, as well as about half a billion websites that rely on REP. These fine grained controls give the publisher the power to decide what they’d like to be crawled on their site and potentially shown to interested users.”
The draft does not change any of the rules established in 1994, it’s just updated for the modern web.
Some of the updated rules include:
- Any URI based transfer protocol can use robots.txt. It’s not limited to HTTP anymore. Can be used for FTP or CoAP as well.
- Developers must parse at least the first 500 kibibytes of a robots.txt.
- A new maximum caching time of 24 hours or cache directive value if available, which gives website owners the flexibility to update their robots.txt whenever they want.
- When a robots.txt file becomes inaccessible due to server failures, known disallowed pages are not crawled for a reasonably long period of time.
Google is fully open to feedback on the proposed draft and says it’s committed to getting it right.