How search engines work and what to optimise for SEO

Executive overview

Search engines index billions of pages and use algorithms to return the most relevant result for any query. Google's algorithm weighs query meaning, content relevance, source quality, and page usability — none of these factors are linear.

Ranking requires matching search intent: the right content type, format, and topic signals. Backlinks act as quality votes; page speed and mobile-friendliness are confirmed ranking factors.

The core insight: SEO is about satisfying searcher intent with high-quality, technically sound content — not keyword repetition.

How Google crawls and indexes the web

• Crawlers (spiders) start from seed URLs and follow hyperlinks to discover new pages continuously
• Discovered pages are stored in Google's search index
• Algorithms categorise queries using keywords, freshness, and other signals to return results in milliseconds
• The knowledge graph goes beyond keyword matching to understand entities: people, places, things

How Google interprets a query

• Search intent is the primary filter: product pages for "slow cooker", recipes for "slow cooker recipes"
• Content type preference is inferred: video results for unboxing queries, image results for maps
• Freshness matters for news and fast-moving topics; less so for stable definitions
• Location personalises results even without an explicit city name in the query
• Past search history shapes autocomplete suggestions

How Google assesses content relevance

• Pages with semantically related keywords rank higher than those stuffing exact-match terms
• A page on driver's licences should naturally include: road, exam, safety, motorcycle — these signal topical depth
• Google explicitly looks for relevant signals to confirm a page answers the query, not just repeats it

How Google evaluates content quality

• Quality is assessed via EAT: expertise, authoritativeness, trustworthiness
• Backlinks are the primary authority signal — treated as votes from other webmasters
• Google uses search quality raters to benchmark results; they do not directly affect rankings
• Spam algorithms detect manipulative link schemes (e.g. reciprocal link exchanges)

Page usability factors

• Page speed: higher load times increase bounce rate; speed is a confirmed mobile ranking factor since 2018
• Mobile-friendliness: Google uses mobile-first indexing; all new sites mobile-first by default since July 2019
• Usability is a proxy for user experience — Google rewards pages that keep searchers satisfied