999 Request Denied
Meaning
A non-standard status code famously used by LinkedIn (and perhaps other services) when a request is blocked by the website's security systems. It often appears when too many requests are made or when scraping is detected.
When to Use
When a service like LinkedIn deliberately blocks a client request (often to discourage bots or excessive scraping) and chooses to respond with a non-standard error code instead of a typical 429 or 403. It indicates the request was not granted, often for vague reasons.
Example
LinkedIn might return 999 Request Denied if someone tries to access certain pages or APIs without proper authentication or if the system suspects abuse (for example, rapid repeated requests scraping user profiles). The response essentially means "no proper response available".
When Not to Use
Do not use in standard web or API design. This code is not part of HTTP and clients may not know how to handle it. It's primarily known due to LinkedIn's historical usage. Use 429, 403, or other appropriate codes for blocking or rate limiting in normal scenarios.
Source
Unofficial (LinkedIn)