Noindex
A noindex directive — a meta tag or an X-Robots-Tag header — tells search engines to keep a URL out of the index even if they can crawl it.
Why it matters
The classic production incident is a staging noindex that ships to live and goes unnoticed for weeks, because nothing in the stack treats it as an error. Catching it is a matter of checking the directive per URL rather than waiting for traffic to fall.
