A backend under load can return 200 most of the time and 503 just often enough that a single manual check never catches it, while Googlebot, hitting the site far more often, sees the pattern clearly. TechySEO records the status code of every URL on every crawl pass, so an intermittent failure shows up as a trend instead of getting lost between snapshots.
Everything else about a page, its content, its design, its keywords, is interpretation. The status code is just a fact: did the server actually return what it was supposed to. A 5xx tells Googlebot the server is unavailable or broken, and if that keeps happening across crawl attempts, Google starts crawling the URL less often and can pull it from the index entirely if the errors don't stop. A 4xx burns crawl budget on a page that has nothing to show for it.
The quieter failure mode is an unexpected 3xx showing up on a page that's supposed to return 200. It hides the real URL from search engines, breaks link equity attribution, and leaves Google uncertain about which version of the content is actually the one to index. None of this requires a dramatic outage. It just requires nobody watching closely enough to notice the code changed.
A single check at a single moment misses the failures that only happen sometimes. A server returning 503 on 5% of requests under load looks perfectly healthy if you happen to check during the other 95%, and intermittent like that is exactly the pattern that erodes Google's crawl trust over weeks without ever producing one obvious incident.
Every category, tracked as a trend, since the failures that matter most are rarely a single bad request.
Track every status code across every crawl pass, and get alerted the moment a pattern shows up, not just when something breaks completely.
