A 60-second test for the soft 404 that Screaming Frog and Semrush both missed solostacklab.net

A soft 404 returns HTTP 200 for a URL that doesn’t exist, often with the homepage instead of an error page. We found ours by accident – a spike in 4xx counts on Cloudflare’s dashboard with no visible paths – then confirmed it with a one-line curl test. Two free crawlers we’d already run against the same site weeks earlier, Screaming Frog and Semrush, never flagged it, because both only request URLs they’ve already discovered through links, and every discovered URL on the site actually existed. The post has the exact curl commands to run it yourself, the before/after response for the paths we probed, the Cloudflare Pages cause (no top-level 404.html), the fix, and what we still don’t know.