When Google crawls a website, the robots.txt file serves as a roadmap, defining what content search engines can or cannot access. But what happens when Google encounters 3xx (Redirection) or 4xx (Client Errors) while fetching this critical file? Let’s explore Google’s crawling behavior, its interpretation of these errors, and best practices for managing them.

How Google Handles 3xx (Redirection) Errors in Robots.txt Fetching

What Are 3xx Redirection Status Codes?

A 3xx status code indicates a redirect, signaling that the requested resource has moved to a new location. Common 3xx status codes include:

• 301 Moved Permanently
• 302 Found (Temporary Redirect)
• 307 Temporary Redirect
• 308 Permanent Redirect

Google’s Approach to Robots.txt Redirection

1. Redirect Limit: Five Hops
   • Google follows up to five redirects when attempting to fetch a robots.txt file.
   • Example:
     • If robots.txt redirects from example.com/robots.txt to site.com/robots.txt and this happens more than five times, Google stops following the redirects.
     • Result: The robots.txt file is considered unreachable and treated as a 404 Not Found.
2. Impact on Crawling
   • If Google encounters more than five redirect hops, it assumes the robots.txt file does not exist, meaning the site has no crawl restrictions.
3. Disallowed URLs in the Redirect Chain
   • If a URL in the redirect chain is disallowed by the robots.txt file, Google cannot fetch the file and treats the site as if it has no restrictions.

What Google Does NOT Follow

Google does not follow the following redirects while fetching robots.txt:

• HTML Redirects: Page-based redirects through <meta> refresh tags
• JavaScript Redirects: Client-side JavaScript-based redirection
• Frames or Embedded Redirects: Frames or iframes pointing to different robots.txt locations

Best Practices for Handling 3xx Errors

1. Use Direct Links: Avoid complex redirect chains for robots.txt files.
2. Minimize Redirect Hops: Ensure the redirect path has fewer than five hops.
3. Avoid Disallowed URLs in Redirect Chains: Ensure robots.txt is not blocked during redirection.
4. Check Redirects Regularly: Use tools like Google Search Console to detect and fix redirect errors.

How Google Handles 4xx (Client) Errors in Robots.txt Fetching

What Are 4xx Client Errors?

A 4xx status code means something is wrong with the request made by Google’s crawlers, typically indicating that the requested file is missing or access is denied. Common 4xx errors include:

• 400 Bad Request: Invalid request sent to the server
• 403 Forbidden: Access denied to the requested file
• 404 Not Found: File not found on the server
• 410 Gone: File permanently removed
• 429 Too Many Requests: Server is overwhelmed with requests

Google’s Treatment of 4xx Errors

1. All 4xx Errors Except 429:
   • Google treats all 4xx errors (except 429) as if the robots.txt file does not exist.
   • Result: Google assumes no crawl restrictions and crawls the site as if robots.txt is missing.
2. Exception – 429 Too Many Requests:
   • A 429 indicates that the server is overwhelmed by too many requests.
   • Google’s Action:
     • It reduces crawl frequency temporarily.
     • It continues retrying robots.txt fetches at intervals.

Special Notes on 401 and 403 Errors

• 401 Unauthorized: If robots.txt requires authentication (which it shouldn’t), Google treats this as robots.txt not existing.
• 403 Forbidden: Google assumes there are no crawl restrictions if a 403 status is returned for robots.txt.

Important Tip:

• Do NOT use 401 or 403 status codes to control crawl rates. They are ignored by Google, and Google continues crawling the site as if there’s no restriction.

Best Practices for Handling 4xx Errors

1. Avoid 4xx Errors for Robots.txt: Ensure the robots.txt file is always available to Google crawlers.
2. Use a Valid robots.txt File: Ensure the file is properly configured and returns 200 OK.
3. Monitor Errors Regularly: Use Google Search Console to check for 4xx issues.
4. Don’t Block Robots.txt with Authentication: Keep it publicly accessible without login requirements.
5. Use Proper Crawl Control Techniques: Control crawling using appropriate robots.txt rules or Google Search Console settings.

Key Pointers To Consider

When 3xx Errors Occur

• Google follows up to five redirect hops while fetching robots.txt.
• Beyond five hops, Google stops following the chain and treats it as a 404.
• Logical redirects like meta refresh or JavaScript-based redirects are not supported.

When 4xx Errors Occur

• All 4xx errors except 429 mean Google assumes no crawl restrictions.
• A 429 Too Many Requests temporarily reduces crawling and prompts retries.
• 401 and 403 errors should never be used to limit Google’s crawl rate.

By ensuring proper handling of robots.txt files and avoiding 3xx and 4xx status errors, webmasters can ensure smooth and effective crawling of their sites by Google’s search engine bots.