You can write Pulitzer-level content and build DA90 links, but if your technical SEO is a mess, none of it matters. Technical SEO quietly undermines your site’s performance, remaining undetected until your rankings plummet.

Here are nine common and costly technical SEO mistakes that marketers, developers, and SEO professionals continue to make, along with suggestions for how to address them.

1. Neglecting mobile optimisation

Google switched to mobile-first indexing years ago. If your site still appears as a clunky desktop relic on mobile devices, you’re losing out on rankings.

Fix it:

• Use responsive design, not a separate mobile URL.
• Avoid intrusive pop-ups and ensure clickable elements aren’t jammed together.
• Test mobile usability in Google Search Console and fix errors fast.

2. Ignoring crawl errors

Crawl errors break the path between your content and Google’s index. Pages that throw server errors, 404s, or timeout issues are black holes for your visibility.

Fix it:

• Monitor crawl stats and errors in Google Search Console.
• Fix broken internal links, eliminate redirect chains, and resolve server issues.
• Crawl your site monthly using tools like Screaming Frog or Sitebulb.

3. Overlooking site speed

People expect pages to load instantly. Google does too. A sluggish site hurts UX, conversion rates, and rankings, all in one blow.

Fix it:

• Compress images, enable caching, and implement a CDN.
• Fix layout shifts and improve time to the first byte.
• Prioritise Core Web Vitals, especially Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS).

4. Poor site architecture and internal linking

If your site structure is a tangled mess, search engines and users get lost. Important pages buried deep in the hierarchy will struggle to rank.

Fix it:

• Use a flat structure; most pages should be within three clicks of the homepage.
• Link topically between related pages, not just using “related posts” plugins.
• Don’t rely on JavaScript-based navs alone; bots aren’t always JS-friendly.

5. Sloppy redirects and broken links

Redirect chains, broken backlinks, and 404 errors not only waste crawl budget but also ruin user trust.

Fix it:

• Audit redirects regularly, keep them one-to-one, and avoid loops.
• Remove or fix broken internal links.
• Customise your 404 page with helpful links or search options.

6. Unstructured, messy URLs

A confusing URL structure is bad for SEO and worse for humans. Stop using long, ugly URLs with random numbers or endless parameters.

Fix it:

• Use clean, descriptive URLs (e.g., /seo-audit-checklist/, not /page?id=4820).
• Avoid dynamic parameters unless absolutely necessary.
• Keep it short, relevant, and consistent.

7. Not using HTTPS

Serving your site over HTTP in 2025 is asking for trouble. It’s a trust-breaker for users and a negative ranking signal for Google.

Fix it:

• Get an SSL certificate and force HTTPS across your domain.
• Update all internal links and canonical tags to use HTTPS.
• Fix mixed content issues, especially on CSS, JS, and image files.

8. Skipping XML sitemap creation

An up-to-date XML sitemap helps Google discover new and updated pages quickly. If you’re not using one, it may make indexing more challenging than necessary.

Fix it:

• Create an XML sitemap with your CMS or a plugin.
• Submit it to Google Search Console.
• Update it automatically whenever you publish or update pages.

9. Missing or misconfigured structured data

Structured data boosts your visibility with rich snippets, but misuse it, or forget it, and you’re invisible in enhanced search results.

Fix it:

• Use schema markup for articles, products, FAQs, events, and more.
• Validate all markup using Google’s Rich Results Test.
• Avoid spammy markup; Google’s not stupid.

Final thoughts

Technical SEO isn’t optional; it’s non-negotiable. You wouldn’t build a house on rotting wood, so stop trying to rank with a broken site. These technical faults won’t just slow growth; they’ll silently reverse it.

Fix them now, before your rankings fall off a cliff.