robotstxt

Robots.txt is a plain text file used by websites to guide web crawlers regarding which parts of a site may be crawled or indexed. It is part of the Robots Exclusion Protocol and is not a security mechanism; it relies on voluntary compliance by crawlers and should not be relied on to protect sensitive data.

The file is placed at the root of a domain, and most crawlers fetch it before indexing. For example, https://example.com/robots.txt. A robots.txt file contains one or more records. Each record begins with one or more User-agent lines that identify the crawler or group of crawlers to which the directives apply. The directives that follow, such as Disallow and Allow, specify URL-path prefixes. A Disallow directive blocks access to a path, while an empty Disallow value or the absence of a Disallow line can indicate that the path is allowed. The Allow directive is used to override a broader Disallow for particular subpaths. Multiple records allow different rules for different crawlers.

Other commonly used directives include Crawl-delay, which requests a delay between requests for some bots, though support varies by crawler, and Sitemap, which points crawlers to a site’s sitemap. The Host directive is supported by a few crawlers to indicate a preferred domain.

Limitations and best practices: robots.txt only expresses preferences and does not prevent access; sensitive data should be protected via server-side access controls. Keep the file up-to-date, test rules with a robots.txt tester, and avoid blocking resources needed for proper rendering or indexing.