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📘 How a search engine works

Search engines must discover a page before they can rank it.

3
lessons
~15 min
to learn
Adults
level
Start the course →

What you’ll learn

  1. Discover pagesExplain crawling, robots.txt, and link-based discovery.Crawlers fetch pages under access rules; links and sitemaps expand what they can find.
  2. Build an indexDescribe indexing and inverted-index retrieval.Fetched pages become searchable records; inverted indexes map terms to candidate pages.
  3. Rank and show answersConnect query interpretation, ranking signals, and results assembly.Engines interpret queries, score candidates with many signals, then present snippets and features.

Questions this course answers

What is the main job of a web crawler?

Crawlers discover and fetch; indexing and ranking happen later.

What does an inverted index mainly speed up?

It maps terms to document lists so retrieval avoids scanning everything.

Order these search steps.

Discovery and indexing precede query-time ranking and presentation.

Grounded in trusted sources

  • Google Search Central, Overview of crawling and indexing: https://developers.google.com/search/docs/crawling-indexing/overview
  • Google Search Central, Ranking systems guide: https://developers.google.com/search/docs/appearance/ranking-systems-guide
  • Microsoft Bing, How Bing delivers search results: https://support.microsoft.com/en-us/bing/how-bing-delivers-search-results
  • Britannica, search engine: https://www.britannica.com/technology/search-engine

Every Wunder lesson is built from real, reputable sources — never invented.

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