Google could increase the checklist of unsupported robots.txt guidelines in its documentation based mostly on evaluation of real-world robots.txt knowledge collected by means of HTTP Archive.
Gary Illyes and Martin Splitt described the undertaking on the most recent episode of Search Off the Report. The work began after a neighborhood member submitted a pull request to Google’s robots.txt repository proposing two new tags be added to the unsupported checklist.
Illyes defined why the workforce broadened the scope past the 2 tags within the PR:
“We tried to not do issues arbitrarily, however quite accumulate knowledge.”
Fairly than add solely the 2 tags proposed, the workforce determined to take a look at the highest 10 or 15 most-used unsupported guidelines. Illyes mentioned the aim was “an honest place to begin, an honest baseline” for documenting the commonest unsupported tags within the wild.
How The Analysis Labored
The workforce used HTTP Archive to check what guidelines web sites use of their robots.txt recordsdata. HTTP Archive runs month-to-month crawls throughout tens of millions of URLs utilizing WebPageTest and shops the leads to Google BigQuery.
The primary try hit a wall. The workforce “rapidly found out that nobody is definitely requesting robots.txt recordsdata” in the course of the default crawl, which means the HTTP Archive datasets don’t sometimes embody robots.txt content material.
After consulting with Barry Pollard and the HTTP Archive neighborhood, the workforce wrote a customized JavaScript parser that extracts robots.txt guidelines line by line. The customized metric was merged earlier than the February crawl, and the ensuing knowledge is now obtainable within the custom_metrics dataset in BigQuery.
What The Knowledge Reveals
The parser extracted each line that matched a field-colon-value sample. Illyes described the ensuing distribution:
“After enable and disallow and consumer agent, the drop is extraordinarily drastic.”
Past these three fields, rule utilization falls into a protracted tail of much less widespread directives, plus junk knowledge from damaged recordsdata that return HTML as an alternative of plain textual content.
Google at the moment helps 4 fields in robots.txt. These fields are user-agent, enable, disallow, and sitemap. The documentation says different fields “aren’t supported” with out itemizing which unsupported fields are commonest within the wild.
Google has clarified that unsupported fields are ignored. The present undertaking extends that work by figuring out particular guidelines Google plans to doc.
The highest 10 to fifteen most-used guidelines past the 4 supported fields are anticipated to be added to Google’s unsupported guidelines checklist. Illyes didn’t identify particular guidelines that may be included.
Typo Tolerance Might Broaden
Illyes mentioned the evaluation additionally surfaced widespread misspellings of the disallow rule:
“I’m most likely going to increase the typos that we settle for.”
His phrasing implies the parser already accepts some misspellings. Illyes didn’t decide to a timeline or identify particular typos.
Why This Issues
Search Console already surfaces some unrecognized robots.txt tags. If Google paperwork extra unsupported directives, that might make its public documentation extra intently replicate the unrecognized tags folks already see surfaced in Search Console.
Wanting Forward
The deliberate replace would have an effect on Google’s public documentation and the way disallow typos are dealt with. Anybody sustaining a robots.txt file with guidelines past user-agent, enable, disallow, and sitemap ought to audit for directives which have by no means labored for Google.
The HTTP Archive knowledge is publicly queryable on BigQuery for anybody who needs to look at the distribution instantly.
Featured Picture: Screenshot from: YouTube.com/GoogleSearchCentral, April 2026.