HTTP status codes carry more meaning than most APIs use. The difference between a 301 and a 302 determines whether ranking signals transfer; the difference between 401 and 403 is authentication versus authorisation. This searchable reference covers every standard code with its practical implications.
301 is permanent and passes ranking signals to the new URL; 302 is temporary and tells search engines to keep the original indexed. Using 302 for a permanent move is a common and costly mistake.
404 means not found, possibly temporarily. 410 means deliberately and permanently gone, and search engines typically drop a 410 URL from the index faster.
A page that says "not found" to the user but returns HTTP 200. Search engines index it as a real page, which wastes crawl budget. Single-page applications produce these very easily.
401 means you have not authenticated, so credentials might help. 403 means you are authenticated but not allowed, so retrying with the same identity will not.
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