An HTTP status code is a three-digit number a web server sends with every response. The code tells the browser and the crawler how the request was handled. The HTTP standard RFC 9110 groups the codes into five classes, by their first digit. You do not see the code on the page itself; it travels with the response.
The five classes and what Google does with them
| Class | Meaning | What Google does |
|---|---|---|
| 1xx | Informational | An interim step, not a final response |
| 2xx | Success, such as 200 | The content moves on to indexing, with no guarantee it will be included |
| 3xx | Redirect, such as 301 | Google follows up to ten hops by default |
| 4xx | Client error, such as 404 | Not indexed; previously indexed URLs drop out over time (429 counts as a server error) |
| 5xx | Server error, such as 503 | Google temporarily slows down crawling; if the error persists, URLs drop out of the index |
The right-hand column follows Google’s explanation in How HTTP status codes affect Google Search.
Common mistake
An error page that returns a 200. A page saying “Product not found” that technically reports success is called a soft 404. Search Console reports these separately. Return a real 404 or 410 when the content is gone.
How do you check it?
You can see the status code in your browser’s developer tools, on the Network tab. Atlas, the research engine developed by Outseen, records the HTTP responses of the pages it investigates. For this and other reasons a page can be missing from Google, see Why is my page not showing in Google?