Web Crawler

Web Crawler

A web crawler, also known as a spider or bot, is a program used by search engines to systematically browse the internet and collect data from websites. It follows hyperlinks from one web page to another, retrieving and indexing information to build a searchable index for search engines.

How Web Crawlers Work

Web crawlers have specific steps that they follow to gather data from websites, update information, and build search engine indexes. These steps include:

Discovery

The web crawler starts the process by visiting a list of known web pages or by fetching a few pages. During this phase, it identifies and extracts hyperlinks from these pages, which serve as starting points for further exploration.

Indexing

As the web crawler discovers new pages through following hyperlinks, it retrieves and processes the content of each page. This process involves extracting text, images, and metadata from the web page. The retrieved information is then stored in a database for future use.

Revisiting

Web crawlers periodically revisit the pages they have already crawled to check for any updates or changes in content. By doing so, they ensure that their index remains up to date and reflects the current state of the web.

Prevention Tips

Webmasters can employ various strategies to control the behavior of web crawlers and ensure that their websites are crawled efficiently. Some of these prevention tips include:

Robots.txt

Webmasters can use a file called "robots.txt" to communicate with web crawlers and specify which areas of their website should or should not be crawled. This file provides instructions to web crawlers on how they should access and interact with a website's content.

Page Design

Organizing website content with clear and crawlable links is crucial to ensure that web crawlers can easily navigate through the website and access all the important information. By employing proper website architecture and including relevant hyperlinks, webmasters can facilitate the crawling process.

Crawl Delay

Webmasters also have the option to control the crawl rate of web crawlers. By adjusting the crawl delay, they can manage the impact of web crawlers on server resources, preventing excessive traffic and potential performance issues. This can be achieved by specifying a delay time between successive requests from the crawler.

Related Terms

• Web Scraping: The process of extracting specific information from web pages, often using automated bots or scripts. Web scraping is commonly performed by web crawlers to gather data from websites.

• Indexing: The method of collecting, parsing, and storing data to facilitate fast and accurate information retrieval. Web crawlers play a crucial role in the indexing process by retrieving and storing information from web pages to build search engine indexes.

[Sources]

• Wikipedia - Web Crawler
• Search Engine Journal - What is a Web Crawler? The Ultimate Guide
• Moz - Web Crawling
• Yext - The Web Crawler: What is it and How Does it Work?
• Sciencedirect - Web Crawlers