| 404 / Not found | Page does not exist | Only if it has links or traffic |
| Soft 404 | Returns 200 but has no real content | Yes — wastes crawl, signals low quality |
| Server error (5xx) | Site failed to respond | Yes — fix urgently |
| Redirect error | Chain, loop, or broken destination | Yes |
| Blocked by robots.txt | Crawler was disallowed | Only if unintentional |
| Excluded by noindex | Directive present | Only if unintentional |
| Discovered — not indexed | Google found it, chose not to index | Often, at scale |
| Crawled — not indexed | Google read it, chose not to index | Often — usually thin content |