Celebrating 30 Years of Robots.txt: Google’s Insight into Its Overlooked Advantages

  • July 2, 2024
  • SEO
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In a recent LinkedIn post, Gary Illyes, an Analyst at Google, shed light on some lesser-known facets of the robots.txt file as it celebrates its 30th anniversary.

The robots.txt file, which plays a crucial role in web crawling and indexing, has been a core element of SEO practices since its introduction.

Here’s one aspect that underscores its ongoing relevance:

Robust Error Handling

Illyes highlighted the file’s exceptional resilience to errors, stating, “robots.txt is virtually error-free,” in his LinkedIn post.

According to Illyes, the parsers of the robots.txt file are intelligently designed to ignore most mistakes without losing functionality. This means that even if you inadvertently add extraneous content or misspell directives, the file will continue to operate effectively.

The parsers typically focus on processing key directives such as user-agent, allow, and disallow while disregarding unrecognized content, ensuring the robustness of your web crawling setup.

Unexpected Feature: Line Comments

Illyes also drew attention to the presence of line comments within robots.txt files. Although he found this feature puzzling given the file’s fault-tolerant nature, he prompted the SEO community to share their thoughts on the matter.

Responses To Illyes’ Post

The SEO community’s feedback on Illyes’ post provided further insights into the practical benefits of the robots.txt file’s error tolerance and the use of line comments.

Andrew C., the Founder of Optimisey, underscored the usefulness of line comments for internal communication. He remarked:

“When working on websites, you can see a line comment as a note from the Dev about what they want that ‘disallow’ line in the file to do.”

Screenshot from LinkedIn, July 2024.

Nima Jafari, an SEO Consultant, emphasized the value of comments in large-scale implementations:

He noted that for extensive robots.txt files, comments can “help developers and the SEO team by providing clues about other lines.”


Screenshot from LinkedIn, July 2024.

Providing a historical perspective, Lyndon NA, a digital marketer, compared the error tolerance of robots.txt to HTML specifications and web browsers. He suggested that this was likely an intentional design choice:

“Robots.txt parsers were made lax so that content might still be accessed (imagine if G had to ditch a site, because someone borked 1 bit of robots.txt?).”


Screenshot from LinkedIn, July 2024.

Why SEJ Cares

Understanding the nuances of the robots.txt file can significantly enhance site optimization efforts. However, while the error-tolerant nature of the file is generally beneficial, it also necessitates careful management to avoid overlooked issues.

What To Do With This Information

  1. Review your robots.txt file: Ensure that it only contains necessary directives and is free from potential errors or misconfigurations.
  2. Be cautious with spelling: Although parsers may ignore misspellings, unintended crawling behaviors could result if they slip through.
  3. Leverage line comments: Use comments to document your robots.txt file for future reference, aiding both developers and SEO teams.

Featured Image: sutadism/Shutterstock

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