Server errors and slow response time on online stores

A product page that returns a server error sells nothing, and a page that takes seconds to start loading loses shoppers before they see it. Search engines notice too: repeated 5xx errors make Google crawl your store less, and pages that keep failing eventually leave the index. Peak sales like Black Friday are when both problems show up, so check them before traffic arrives.

What Google does with server errors

Google's documentation on HTTP status codes is clear:

• 5xx and 429 responses make Google's crawlers temporarily slow down. A 429 (too many requests) is treated as a sign the server is overloaded.
• Content returned with a 5xx status is ignored.
• Already indexed URLs are kept for a while, but URLs that persistently return a server error are removed from the index.
• Once the server answers with 2xx again, the crawl rate recovers gradually.

A short incident is not a disaster. A store that throws errors for days, or on a large share of its pages, risks both lost sales and lost visibility.

Why response time matters

Time to first byte (TTFB) is how long the server takes to start sending the page. Everything else waits for it: images, scripts, rendering. A slow TTFB pushes back Largest Contentful Paint, one of the Core Web Vitals, and shoppers on mobile feel it first.

Common causes on online stores:

• Pages built on every request without full-page cache, especially category pages with many filters.
• Slow database queries or too many apps and plugins running on each page.
• No CDN, so every visitor hits the origin server.
• Undersized hosting that is fine on a quiet Tuesday and saturated during a sale.

Get ready for peak traffic

1. Measure today. Check the response time of your home, category and product pages, and look for 5xx in your server logs and in Search Console's crawl stats.
2. Turn on caching. Full-page cache for anonymous visitors, plus a CDN for static files and, where possible, HTML.
3. Load test your busiest pages at a few times your normal traffic, well before the sale.
4. Plan maintenance outside peaks, and serve a short 503 with a Retry-After header if you must go offline.
5. Watch errors live during the sale: an alert on 5xx rates is worth more than a report the next day.

For the rest of your preparation, see the Black Friday checklist.

How Averifly helps

Averifly's technical rules flag pages that return a server error and stores where at least three pages take more than 800 ms to respond, along with redirect chains and broken internal links. Run a free scan before your next peak, and see our rules for the full list of checks.