Redirect Loop

Two or more URLs that redirect to each other endlessly, so no page is ever served.

They usually come from conflicting rules: one forcing a trailing slash, another removing it; one forcing HTTPS, another forcing a locale.

Reproduce with a header trace rather than a browser, which hides the loop behind a generic error.

A loop is a total outage for that URL — for visitors and for crawlers alike.

Because it often affects only one segment or one locale, it can run for weeks before anyone reports it.