Question
Why are HTTP errors such as 404, 401, etc. displayed in an onpage analysis even though the linked pages are accessible?
Answer
A web browser uses GET, which is answered correctly by the web server.
XOVI uses HEAD requests to check external links.
In the onpage area, the HTTP code of the domain can be checked under Onpage > HTTP header analysis.
The pages that are displayed with an HTTP error in the onpage analysis responded to HEAD requests from the XOVI crawler with this HTTP error code.
According to the official specification, the response of a GET should match that of a HEAD:
The HEAD method is identical to GET except that the server MUST NOT
return a message-body in the response.
...
This method is often used for testing hypertext links for validity, accessibility, and recent modification.
Web servers / applications that do not follow these rules behave incorrectly.
Unfortunately, XOVI has no influence on the correct configuration of web servers and web applications and can therefore only display what comes back as a response from the linked web server.
GET requests would have a massive impact on the traffic generated by the XOVI crawler and also have a negative impact on the speed of the onpage crawl.