Detecting and Fixing Crawling Errors

What are crawling errors?

Crawling errors occur when a search engine crawler cannot access a website or individual pages. The consequence is serious: what Google can't crawl doesn't make it into the index – and therefore has no chance of ranking or being cited by AI systems.

A page's path into the search results runs through three stages: crawling (bots discover URLs and fetch them), indexing (the content is analyzed and stored) and ranking (matching pages are sorted for a search query). Crawling errors interrupt this process at the very first step. That's why fixing them is one of the most important tasks in technical SEO.

Types of crawling errors

Crawling errors fall into two categories: those affecting the entire website and those blocking individual URLs.

Errors at the website level

These errors hinder access to the entire website or large parts of it – and therefore have the highest priority.

• DNS errors: The Domain Name System translates domain names into IP addresses. If the crawler can't reach the server via the domain name, a DNS error is present. Causes include outages at the DNS provider or configuration problems.
• Server errors (5xx): Codes like 500 Internal Server Error or 503 Service Unavailable signal that the server was reachable but couldn't process the request – often due to overload, maintenance or misconfiguration. Persistent 5xx errors cause Google to throttle crawling.
• Problems with the robots.txt: If the robots.txt is faulty or unreachable, it can unintentionally block important pages or confuse the crawler.

Errors at the URL level

These errors affect individual pages. A deeper look at the underlying codes is worthwhile in the article HTTP status codes.

• 404 Not Found: The requested URL no longer exists – deleted, moved without a redirect, or a broken link.
• Soft 404: The page technically returns a 200 OK but reads like an error page (thin content, “product unavailable” with no alternatives). Google often treats it like a real 404 error.
• 403 Forbidden: The resource exists, but access is denied – through firewall rules, server permissions or required logins.
• Redirect errors: Problems arise with redirect chains (several redirects in a row) or loops. The right way to do it is shown in Redirects.

Identifying crawling errors

The most important tool is the Google Search Console (GSC). Here's how to proceed:

1. Select the property: Sign in to the Search Console and choose the website to check.
2. Open the indexing report: Under “Indexing” > “Pages,” you see the status of all known URLs.

3. Analyze errors: Focus on the “Not indexed” section. Watch for entries like “Server error (5xx),” “Redirect error,” “Not found (404),” “Blocked by robots.txt,” “Soft 404” or “Access forbidden (403).”

4. Show details: A click on an error type lists the affected URLs – that's how you spot patterns.

5. Use the URL Inspection tool: For a single URL, the tool shows how Google last crawled it and whether problems occurred.

In addition, SEO crawling tools like Screaming Frog or the site audit features of Semrush and Ahrefs help by running through your website like a bot. For the most accurate view of the actual server responses to bots, log file analysis is unbeatable.

Fixing crawling errors

Fix errors systematically and prioritize them: first those affecting the entire website, then important individual pages with a lot of traffic or many backlinks, and finally unimportant pages. This table summarizes the typical solutions:

By the way, a 404 error is not inherently bad: for permanently removed pages, a clean 404 or 410 status is the right signal. It only becomes a problem when important pages suddenly return 404 or valuable links point to nothing.

Avoiding crawling errors

Proactive maintenance prevents many problems from the start:

• Regular audits: Check your website monthly or quarterly with the GSC or SEO crawling tools.
• Enable GSC notifications: This way you learn about new errors early.
• Maintain internal linking: Fix broken links and make sure important pages are easy to reach. The basics are covered under internal linking.
• Keep the sitemap current: A well-maintained XML sitemap helps crawlers find all important URLs.
• Optimize load time: Fast pages improve crawl efficiency and save crawl budget. Approaches are covered under optimizing PageSpeed.

Conclusion

Crawling errors significantly impair a website’s visibility because they block the path into the index. Those who know the error types, systematically identify them with the Search Console and fix them in a targeted way lay the foundation for sustainable SEO success. This work is not a one-off project but an ongoing process of monitoring, maintenance and optimization.