Disallow

Disallow is a verb meaning to refuse permission or to prohibit an action. It can describe formal prohibitions in law, policy, contracts, or everyday speech. A thing that is disallowed is prohibited or not permitted.

In computing and on the web, Disallow is a directive used in the robots exclusion protocol within a robots.txt file to indicate that certain paths should not be accessed by web crawlers. The directive is typically paired with a User-agent field, for example: User-agent: * followed by Disallow: /private/. Crawlers that honor robots.txt are expected to refrain from fetching disallowed paths. However, adherence is voluntary; some bots ignore the file, and robots.txt does not guarantee that disallowed content will not be indexed if linked elsewhere. For indexing control, a noindex directive or meta tag is sometimes used, though support varies.

Origin and scope: The robots.txt standard emerged in the early days of the web and is not a formal security mechanism. It is intended to guide compliant crawlers and reduce server load, not to enforce access control. Disallow can be circumvented by direct URL access, non-compliant agents, or misconfigurations.

Other uses: In general language and in policy writing, to disallow means to prohibit or forbid. The term is often found in rules, guidelines, and software configuration where certain actions or features are explicitly not permitted.