Does Google really over-cache your site's resources?

What does "over-caching" really mean for Google?

When Martin Splitt talks about a "very aggressive" cache, he refers to a conservative strategy: Google prefers to keep a functioning version of a resource rather than risk losing it. The engine stores CSS files, JavaScript, images and other assets for extended periods, even if these resources have been modified or are temporarily inaccessible on the server side.

This approach is based on a simple logic: websites rarely make changes to their critical resources multiple times a day. Thus, Google optimizes its crawl budget by not systematically refetching every file on each bot visit. The engine focuses on the HTML of the pages and reuses already cached assets.

Why doesn't Google fetch resources on every rendering?

Fetching all resources on each crawl would represent a colossal server load — for both you and Google. The engine indexes billions of pages. If Googlebot had to redownload each CSS, every font, every third-party script on each visit, the web would collapse under the bandwidth consumed.

Google thus applies freshness heuristics. The engine detects when a file changes (via HTTP headers, ETags, modification dates) and decides whether to refetch it. In most cases, a stylesheet or JS bundle remains stable for weeks or even months. The cache performs its role as a buffer.

What happens if a resource is broken?

Martin Splitt states that Google retries renderings when necessary. If the engine detects that a page does not display correctly (severe layout shift, missing content, critical JS errors), it may restart the rendering a few days later. This policy tolerates temporary incidents — maintenance, floating CDN, occasional 500 errors.

Let’s be honest: this tolerance has its limits. If your main CSS file returns a 404 for three weeks, Google will eventually index your page with a broken rendering. The "retry" is not an infinite guarantee. It’s a lifeline, not a deployment strategy.

• Google's cache keeps resources for variable durations — usually several weeks for stable assets.
• A temporary error (500, timeout) does not immediately trigger a broken rendering — Google reuses the cached version.
• The engine retries failed renderings, but this policy is not documented with specific timelines.
• Changes to resources are not detected instantly — expect several days before a new CSS is taken into account.
• The crawl budget is optimized: Google only refetches the resources it deems potentially modified.

Is this statement consistent with real-world observations?

Yes, and it is one of the most empirically verifiable statements. SEOs using tools like OnCrawl or Botify regularly find that Googlebot does not refetch assets on every pass. The server logs show that the bot crawls HTML daily but only touches CSS/JS on average every 7 to 21 days — sometimes longer if the site is stable.

This behavior is particularly noticeable on news sites: Google crawls new pages multiple times a day, but the overall resources (header.css, bundle.js) remain cached for weeks. This aligns with an over-caching strategy.

What nuances should be added to this reassuring discourse?

The problem is that this tolerance can mask critical errors. If you deploy a new CSS that breaks the mobile rendering and Google is still using the old cached version, you won’t see any immediate impact in the Search Console. You might think everything is okay for two weeks — until Google finally refetches the resource and indexes your site with a broken layout.

Martin Splitt says, "it's normally not a problem" — but [To be verified]: what is the definition of "momentarily broken"? An hour? A day? A week? Google provides no figures. This gray area makes it difficult to devise any robust deployment strategy. If you fix a CSS bug in production, you have no guarantee on the propagation delay in the index.

When does this rule not apply?

Google over-caches stable and accessible resources. If your CDN consistently returns 403 errors or if your JS files are blocked by robots.txt, the cache does not help: Google has nothing to cache. Similarly, dynamically generated resources with random query strings (e.g., style.css?v=1234567890) can bypass the cache if they change with every crawl.

Sites in migration or redesign are also in a risky zone. If you massively change your resource URLs (new CDN, new build hash), Google has to refetch everything — and this takes time. During this period, you might have an inconsistent mix of old and new resources, leading to shaky renderings.

What should you do to take advantage of this over-caching?

First, ensure that your critical resources are accessible at all times. Google can tolerate a temporary error, but if your primary CSS returns 500 errors for 48 hours, you’re playing with fire. Use a robust CDN with automatic failover and monitor the uptime of your assets with tools like Pingdom or UptimeRobot.

Next, leverage HTTP cache headers wisely. A well-configured Cache-Control (e.g., max-age=2592000 for a month) indicates to Google that the resource is stable. The engine can then adjust its refetch frequency. Conversely, a no-cache on each file forces Google to check for freshness on every crawl — which unnecessarily consumes crawl budget.

What mistakes should be absolutely avoided?

Never deploy a major CSS/JS overhaul without explicit versioning. If you overwrite style.css with radically different content, it might take Google weeks to notice. Prefer a fingerprinting system (e.g., style.abc123.css) that forces immediate refetching. Webpack, Vite, Parcel, and similar tools come with this functionality natively.

Also, avoid blocking resources in robots.txt "to save crawl budget." Google cannot over-cache what it has never been able to fetch. If a CSS is blocked and then unblocked, the engine starts from scratch — and your rendering might remain broken for several crawl cycles. This is a classic trap during migration.

How can I verify if my site is benefiting from this cache?

Analyze your server logs. Compare the crawl frequency of HTML (User-agent: Googlebot) versus that of assets (same User-agent, but for resource URLs). If the bot crawls your pages 3 times a day but your CSS/JS once a week, that's a good sign: the cache is doing its job. A low gap signals a caching issue or overly volatile resources.

Use the Search Console to monitor rendering errors. If Google detects layout issues or missing content, it might be that a cached resource is outdated or that the "retry" did not work. Cross-reference with your deployments: a spike in errors two weeks after a CSS release often indicates a cache lag.

• Set consistent Cache-Control headers (max-age of 1 to 3 months for stable assets).
• Use a fingerprinting or versioning system for critical CSS/JS (e.g., bundle.abc123.js).
• Never block rendering resources in robots.txt — Google must be able to fetch them at least once.
• Monitor the uptime of your CDN and assets: a single 500 error is acceptable, but not 48 hours of downtime.
• Analyze your server logs monthly to check the refetch frequency of resources by Googlebot.
• Cross-reference rendering errors in the Search Console with your deployment dates to detect cache delays.