How do search engines work? Google, Bing and Co.
Search engines are software systems that systematically crawl the internet (crawling), store the found content in a database (indexing), and display the most relevant results in an ordered list when a search query is made (ranking).
Key Takeaways
- ✓Search engines work in three steps: Crawling, indexing, ranking
- ✓Googlebot crawls billions of pages, following links from page to page
- ✓The Google Index contains hundreds of billions of web pages
- ✓Ranking is based on over 200 signals, including relevance, authority and user experience
- ✓AI search systems complement this process with a synthesis layer
To understand SEO, you must first understand how search engines work. The process can be divided into three phases: Crawling, Indexing, and Ranking.
Phase 1: Crawling
Search engines deploy automated programs called crawlers or spiders. Google's crawler is called Googlebot. It visits web pages, reads their content, and follows links on the page to discover additional pages. This process runs continuously and captures billions of pages daily.
The robots.txt file controls which areas of a website may be crawled. The XML Sitemap provides search engines with a structured overview of all important pages. Both files are fundamental tools of technical SEO.
Phase 2: Indexing
After Crawling, Google analyzes the page content: text, images, videos, and structured data. The extracted information is stored in the Google Index, a massive database with hundreds of billions of entries.
Not every crawled page gets indexed. Google can exclude pages from indexing if they contain duplicate content, are of poor quality, or have technical issues. Google Search Console shows the indexing status of each page.
Phase 3: Ranking
When a user enters a search query, Google searches the index for relevant pages and orders them by relevance. The ranking is based on over 200 signals, including content relevance, page authority (backlinks), user experience (Core Web Vitals), E-E-A-T signals, and many other factors.
The ranking algorithm is continuously adjusted. Google performs thousands of updates annually, including several major core updates. 2025 saw four confirmed core updates.
The AI Extension: Synthesis
Since 2024, there has been a fourth phase: AI synthesis. Google AI Overviews, ChatGPT, and Perplexity extract information from multiple indexed sources and synthesize a coherent answer from them. This synthesis layer fundamentally changes how users interact with search results.
Differences Between Search Engines
Google dominates the DACH market with over 90 percent market share. Bing holds about 4.8 percent but is strategically important because ChatGPT Search and Ecosia use Bing's index. Perplexity operates its own crawler with near-real-time indexing.
Data & Statistics
Googles Index enthält hunderte Milliarden Webseiten
Google (2025)Googlebot entdeckt täglich Milliarden neuer und aktualisierter Seiten
Google Search Central (2025)“”
— Gary Illyes, Google Search Analyst
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— Danny Sullivan, Google Search Liaison