What do the HTTP status codes that you see in Plesk server logs mean in general?

Question

• What do the HTTP status codes that you see in Plesk server logs mean in general?

Answer

When a client (for example, a web browser, API client, or search engine crawler) sends an HTTP request to a server, the server responds with an HTTP status code. Status codes are three-digit numbers that indicate whether the request was successful, failed, or requires additional action.

Correct handling of HTTP status codes is essential for:

• Website troubleshooting
• SEO and search engine indexing
• Application debugging
• Web server configuration (Apache, nginx, IIS)

How HTTP Status Codes Are Structured

HTTP status codes are grouped into five categories:

Status Codes vs. Status Messages

What clients actually rely on

Clients rely on the numeric HTTP status code itself, not on the accompanying textual message. The message is informational only and does not influence how clients or crawlers process the response.

Examples:

• 200 OK
• 404 Not Found

HTTP version differences

• HTTP/1.1: Includes both a numeric status code and a message
• HTTP/2 and HTTP/3: Only the numeric status code is sent

This change was introduced to improve performance by reducing unnecessary bytes transferred over the network.

Note: Some testing tools use HTTP/1.1 only, which is why status messages may still appear in their output.

Informational Responses (1xx)

Informational responses indicate that the request was received and understood, but processing has not yet completed. These responses are temporary and are followed by a final response.

These responses are rarely visible in browsers or common testing tools.

Successful Responses (2xx)

Successful response codes indicate that the server processed the request correctly.

Search engine behavior

• 200 OK: Content may be processed and indexed
• 204 No Content: May be treated as missing content and flagged as a soft 404

Redirection Responses (3xx)

Redirection responses indicate that additional action is required to access the requested resource, most commonly by redirecting to another URL.

Search engines typically follow multiple redirects, but excessive redirect chains may result in indexing errors.

Client Error Responses (4xx)

Client error responses indicate that the server cannot process the request due to a client-side issue.

URLs returning 4xx errors are not indexed by search engines. Persisting errors may lead to removal from search results.

Soft 404 Errors

A soft 404 occurs when a page returns a 200 OK status code, but the content indicates that the page does not exist or contains no meaningful content.

This results in a poor user experience and conflicting signals for crawlers. Search engines may exclude such pages from search results and report them as soft 404 errors.

Best practice: Return proper 404 or 410 status codes for missing or removed content.

Server Error Responses (5xx)

Server error responses indicate that the server was unable to process a valid request due to internal problems.

Search engines slow down crawling when frequent 5xx errors are detected. Persisting server errors may result in de-indexing of affected pages.

Best Practices

• Always return a status code that matches the actual state of the content
• Avoid returning 200 OK for error or empty pages
• Use 301 or 308 for permanent redirects
• Use 410 Gone for permanently removed content
• Monitor 4xx and 5xx errors in Plesk and Search Console
• Treat recurring 5xx errors as high-priority issues