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Official statement

The robots.txt file must return the correct response code. If it doesn't exist, the server must return 404. If a server error is returned, Google treats it as a problem and won't crawl the site. This has always been the case.
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Extracted from a Google Search Central video

💬 EN 📅 14/03/2022 ✂ 16 statements
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Other statements from this video 15
  1. Les fluctuations de classement sont-elles vraiment normales ou cachent-elles un problème technique ?
  2. Google utilise-t-il vraiment un seul index mondial pour tous les pays ?
  3. Faut-il encore se fier aux résultats de la requête site: pour diagnostiquer l'indexation ?
  4. L'engagement utilisateur influence-t-il réellement le classement Google ?
  5. Pourquoi les pages à fort trafic pèsent-elles plus dans le score Core Web Vitals ?
  6. Google segmente-t-il vraiment les sites par type de template pour évaluer la Page Experience ?
  7. Combien de liens internes faut-il placer par page pour optimiser son SEO ?
  8. Pourquoi la structure en arbre de votre maillage interne compte-t-elle vraiment pour Google ?
  9. La distance depuis la homepage influence-t-elle vraiment la vitesse d'indexation ?
  10. Pourquoi la structure d'URL n'a-t-elle aucune importance pour Google ?
  11. Pourquoi les positions Search Console ne reflètent-elles pas la réalité du classement ?
  12. Google distingue-t-il vraiment 'edit video' et 'video editor' comme des intentions différentes ?
  13. Le balisage FAQ doit-il obligatoirement figurer sur la page indexée pour générer un rich snippet ?
  14. Les liens en footer ont-ils la même valeur SEO que les liens dans le contenu ?
  15. L'indexation mobile-first a-t-elle un impact sur vos classements Google ?
📅
Official statement from (4 years ago)
TL;DR

Google requires that the robots.txt file return either a 200 (file exists) or a 404 (file absent) status code. If the server returns a 5xx error, Googlebot considers it a technical problem and suspends crawling the site. This rule is nothing new — it has applied since Google's earliest days.

What you need to understand

Why Does Google Stop Crawling When Robots.txt Returns a 5xx Error?

When Googlebot requests /robots.txt, it expects a clear response: the file exists (200) or it doesn't (404). In either case, the bot knows how to proceed.

If the server returns a 5xx error (500, 503, etc.), Google interprets this as a temporary server malfunction. As a precaution, it suspends crawling to avoid overwhelming an already struggling site. This isn't a penalty — it's a protective measure.

What Actually Happens If Robots.txt Returns a 5xx Code?

The site becomes temporarily uncrawlable. Googlebot will return to try again later, but as long as the error persists, no pages will be explored.

If the problem lasts several days, pages can begin disappearing from the index due to lack of refresh. New pages won't be discovered. It's a complete blockage of the crawl pipeline.

Does This Rule Apply to Other HTTP Status Codes Too?

No. Only 5xx errors trigger this cautious behavior. A 404 simply means "no robots.txt, I'll crawl everything." A 200 indicates a valid file to respect.

3xx redirects are generally followed, but Google recommends avoiding complex redirect chains on this critical file. A 401/403 code is treated as intentional blocking — equivalent to a complete Disallow: / .

  • A 404 on robots.txt = no crawl restrictions
  • A 200 on robots.txt = file is read and applied
  • A 5xx error = crawl suspended until resolved
  • 3xx redirects work but are discouraged for this critical file
  • A 401/403 is equivalent to blocking the entire site

SEO Expert opinion

Does This Statement Really Reflect Real-World Behavior?

Yes, and it's verifiable in minutes. Trigger a 500 error on your robots.txt in dev or preprod, monitor Search Console: you'll see crawling drop sharply.

This behavior has been documented for years in official guidelines, but many developers still don't know about it. Result: a poorly tested update, a CDN switching to error mode, and suddenly nothing moves on the indexation side.

Why Do Some Sites Temporarily Escape This Rule?

Google can show temporary tolerance on high-authority sites or those with stable crawl history. If your robots.txt crashes for 15 minutes, Googlebot won't panic immediately.

But don't rely on it. A new site, a low-authority domain, or an error persisting for several hours? Crawling stops dead. [To be verified]: the exact tolerance duration varies by site, and Google publishes no official figures.

Should You Really Monitor This File Like a Critical Resource?

Absolutely. The robots.txt file is one of the first resources queried by all bots — Google, Bing, and even more aggressive third-party crawlers.

A server buckling under load can start returning 503s precisely on this file. And there's the domino effect: no legitimate crawl, so no fresh indexing, so visibility drops. All because a 200-byte text file is no longer accessible.

Warning: Some CDNs or WAFs can block access to /robots.txt if misconfigured (overly aggressive rate limiting, geo-blocking). Verify that the Googlebot User-Agent is explicitly allowed.

Practical impact and recommendations

How Can You Verify That Your Robots.txt Returns the Correct HTTP Code?

Use curl from the command line: curl -I https://yoursite.com/robots.txt. The first line should display HTTP/1.1 200 or HTTP/1.1 404.

On the Search Console side, the URL Inspection tool also tests robots.txt automatically. If Google detects a problem, it alerts you directly in the "Coverage" section.

What Should You Do If Your Server Regularly Returns 5xx Errors?

First, isolate the cause: server load, database timeout, CDN issue? Your server logs are your best ally.

If the problem is traffic spikes, consider serving robots.txt from a static cache or dedicated CDN. This file rarely changes — no reason it should hit your entire application stack.

What Mistakes Should You Avoid When Managing Robots.txt?

Never block this file through another mechanism (HTTP authentication, overly strict IP whitelisting). Googlebot must be able to access it before crawling anything else.

Also avoid generating this file dynamically if your CMS is fragile. A static robots.txt, version-controlled, and served directly by your web server is infinitely more reliable.

  • Regularly test the HTTP code returned by /robots.txt (200 or 404 only)
  • Set up monitoring alerts on this file (Uptime Robot, Pingdom, etc.)
  • Verify that your CDN/WAF doesn't interfere with robots.txt access
  • Serve this file statically rather than through dynamic generation
  • Check Search Console weekly to detect crawl anomalies
  • Document the exact file path in your infrastructure (server root, CDN, cache)
A failing robots.txt can paralyze Google's crawl in hours. It's a critical technical file that deserves as much attention as your XML sitemap or 301 redirects. If your infrastructure is complex — multi-server setups, multi-layer CDNs, heavy application stacks — these verifications can quickly become time-consuming. Having your technical setup audited by an SEO-specialized agency lets you detect these weak points before they impact your indexation.

❓ Frequently Asked Questions

Un site sans robots.txt peut-il être correctement indexé par Google ?
Oui, absolument. Un 404 sur robots.txt signifie simplement qu'il n'y a aucune restriction de crawl. Googlebot explorera alors toutes les pages accessibles.
Combien de temps Google tolère-t-il une erreur 5xx sur robots.txt avant de suspendre le crawl ?
Google ne communique pas de durée précise. Sur un site à forte autorité, quelques minutes peuvent passer inaperçues. Sur un site récent, la suspension peut être quasi immédiate.
Est-ce que Bing et les autres moteurs appliquent la même règle ?
Oui, le comportement est similaire. Tous les bots respectent les erreurs 5xx comme un signal de serveur indisponible et suspendent temporairement le crawl.
Peut-on rediriger /robots.txt vers une autre URL ?
Techniquement oui (301/302), mais c'est déconseillé. Google suit la redirection, mais cela ajoute une latence inutile et un point de défaillance supplémentaire.
Que se passe-t-il si robots.txt retourne un code 403 (Forbidden) ?
Google interprète un 403 comme un blocage volontaire équivalent à un Disallow: / complet. Aucune page du site ne sera crawlée.
🏷 Related Topics
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