What Is Technical SEO: A Plain-English Guide

What technical SEO actually covers

Technical SEO is the set of website infrastructure factors that affect search engine performance. It is concerned with how easily search engines can find pages (crawl), understand them (render), store them (index), and serve them quickly to users (page experience).

A site can have outstanding content and still fail because of technical issues: pages blocked in robots.txt, important content rendered only via JavaScript that Googlebot cannot execute, slow servers, broken internal links, duplicate content from URL parameters. Fixing the technical layer often unlocks ranking improvements without producing any new content at all.

Crawlability

Crawlability is whether search engine bots can reach a page. The main controls are robots.txt (a file telling crawlers which paths they can and cannot fetch - misconfigured robots.txt is one of the most common technical SEO failures), internal links (orphan pages often go unindexed), XML sitemaps (submitted to Google Search Console and Bing Webmaster Tools), and crawl budget management for large sites.

Indexation

Indexation is whether crawled pages get stored in Google's index. Common indexation issues: noindex tags accidentally left on from staging templates; canonical tags pointing elsewhere (a page whose canonical points to a different URL will usually not be indexed); soft 404s and thin content that Google judges as low-value; and duplicate content where multiple URLs serve the same content.

The Google Search Console "Pages" report shows indexation status with reasons for exclusions and is the primary diagnostic.

Site speed and Core Web Vitals

Google's Core Web Vitals measure user experience around loading, interactivity, and visual stability: Largest Contentful Paint (LCP) - time until main content loads, good under 2.5 seconds; Interaction to Next Paint (INP) - page response to interaction, good under 200 milliseconds; Cumulative Layout Shift (CLS) - how much the page jumps as it loads, good under 0.1.

Core Web Vitals are a confirmed ranking factor. Common fixes include image compression and lazy loading, deferring non-critical JavaScript, reserving space for ads and embeds, and using a CDN.

Structured data

Structured data (most commonly JSON-LD using schema.org vocabulary) describes what a page is about and lets Google display rich results: review stars, FAQ accordions, product prices, event dates, breadcrumbs. Common schema types used by UK businesses include Organization, LocalBusiness, Article, FAQPage, Product, Review, and BreadcrumbList.

Schema is validated using Google's Rich Results Test. Incorrect or misleading schema can trigger manual actions.

Technical SEO checklist

• robots.txt allows important content, blocks staging and admin paths
• XML sitemap submitted to Search Console, no errors
• HTTPS enforced site-wide, no mixed content
• One canonical URL per page, no canonical loops
• Mobile-friendly per Google's mobile-friendly test
• Core Web Vitals in the "Good" range for 75% of URLs
• Schema markup present for relevant content types and validating without errors
• Important pages within three clicks of the homepage
• 404s monitored, important broken inbound links redirected
• JavaScript-rendered content tested in Google's URL Inspection tool

Frequently asked questions

How often should a technical SEO audit happen?

Annual at minimum. Quarterly is sensible for ecommerce or content-heavy sites. A targeted audit should follow any site migration, redesign, CMS change, or major Google update.

Can technical SEO be done in-house?

Yes, with the right skills. The blockers are usually access (developer time to implement changes) and tooling cost (Ahrefs, Semrush, Screaming Frog licences). Smaller teams often use a specialist agency or consultant for the audit and handle implementation in-house.

What is the difference between technical SEO and on-page SEO?

Technical SEO is about site infrastructure: crawling, indexing, speed, schema. On-page SEO is about individual page optimisation: titles, headings, content quality, internal links, intent match. The two overlap at the page level but serve different concerns.

Is JavaScript bad for SEO?

Not inherently. Google can render JavaScript, but rendering happens in a second pass and adds latency. Content rendered only via JavaScript without a server-side fallback is more vulnerable to indexation issues than HTML content. Server-side rendering or static generation is generally safer for SEO-critical pages.

Do Core Web Vitals affect rankings on mobile and desktop?

Yes, both. Google rolled page experience signals into mobile rankings in 2021 and into desktop rankings in 2022. The same metrics apply, measured separately for each device class.

Sources

• Google Search Central documentation at developers.google.com/search
• web.dev Core Web Vitals documentation at web.dev/vitals
• Schema.org vocabulary specifications at schema.org