Definition

Soft 404

A soft 404 is a page that returns HTTP 200 ("success") while its content says the page doesn't exist — "product no longer available", "page not found" — so status-code-based checkers see a healthy page where a human sees an error.

Soft 404s are why serious link checking reads page content, not just status codes. The subtlety is doing it without false positives: e-commerce themes embed error strings in every page's JavaScript, so the check must run against the visible text a visitor actually sees — a distinction that separates accurate validators from noisy ones.