How Search Works

From algorithms to answers.

Part 2 of 3

Algorithms

We write programs  & formulasto deliver the best results possible.


As you search

algorithmsget to work looking for clues
to better understand what
you mean.

Based on these clues, we pull relevant documents from the index.

We thenrankthe results

We don't accept payment to increase a site's ranking.
The most relevant results appear first.

using over200 factors.

The search lab

Our algorithms are constantly changing. These changes begin as ideas in the minds of our engineers. They take these ideas and run experiments, analyze the results, tweak them, and run them again and again.

Explore theSearch
Lab
All this happens in
1/8th of a second.

resultscan take a variety of forms:

  1. 1

    Knowledge Graph

    Provides results based on a database of real world people, places, things, and the connections between them.

  2. 2

    Snippets

    Shows small previews of information, such as a page's title and short descriptive text, for each search result.

  3. 3

    News

    Includes results from online newspapers and blogs from around the world.

  1. 1

    Knowledge Graph

    Provides results based on a database of real world people, places, things, and the connections between them.

  2. 8

    Voice Search

    With the Google Search App, simply say what you want and get answers spoken right back to you.

  3. 9

    Mobile

    Includes improvements designed specifically for mobile devices, such as tablets and smartphones.

  1. 4

    Answers

    Displays immediate answers and information for things such as the weather, sports scores and quick facts.

  2. 5

    Videos

    Shows video-based results with thumbnails so you can quickly decide which video to watch.

  3. 6

    Images

    Shows you image-based results with thumbnails so you can decide which page to visit from just a glance.

  4. 7

    Refinements

    Provides features like "Advanced Search," related searches, and other search tools, all of which help you fine-tune your search.

As You Search

  1. Spelling

    Identifies and corrects possible spelling errors and provides alternatives.

  2. Autocomplete

    Predicts what you might be searching for.
    This includes understanding terms with more
    than one meaning.

  3. Synonyms

    Recognizes words with similar meanings.

  4. Query Understanding

    Gets to the deeper meaning of the words you type.

  5. Search Methods

    Creates new ways to search, including "search by image" and "voice search."

  6. Google Instant

    Displays immediate results as you type.

Ranking

  1. Site & Page Quality

    Uses a set of signals to determine how trustworthy, reputable, or authoritative a source is. (One of these signals is PageRank, one of Google's first algorithms, which looks at links between pages to determine their relevance.)

  2. Freshness

    Shows the latest news and information. This includes gathering timely results when you're searching specific dates.

  3. SafeSearch

    Reduces the amount of adult web pages,
    images, and videos in your results.

  4. User Context

    Provides more relevant results based on
    geographic region, Web History, and other factors.

  5. Translation and Internationalization

    Tailors results based on your language and country.

  6. Universal Search

    Blends relevant content, such as images, news, maps, videos, and your personal content, into a single unified search results page.

The Search Lab

  1. Precision Evaluation

    In a precision evaluation, Search evaluators (people who are trained to evaluate search quality) rate the usefulness of individual results for a given search.

    In a typical year, we run over 40,000 precision evaluations.
    Curious about what search evaluators are looking for?
    Download the Guidelines

  2. Side-by-Side Experiment

    In a side-by-side experiment, evaluators review two different sets of search results: one from the old algorithm and one from the experimental one.
    They analyze the results and give us feedback on
    the differences.

    In a typical year, we run over 9,000 side-by-side experiments.

  3. Live Traffic Experiment

    In live traffic experiments, we change Search for a small percentage of real Google users and see how it affects their experience. We carefully analyze the results to understand whether the change is
    an improvement.

    In a typical year, we run over 7,000 live traffic experiments.

  4. Launch

    Our lead engineers review the data from the experiments and decide if the change should go to launch for all Google users.

    Based on all these experiments, we'll launch over 500 search improvements in a typical year.

  5. Inside the Search Lab

    Here's a short video we put together that gives a sense of the work that goes into improving Search.

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