A web crawler, also known as a web spider, is a computer program that systematically browses the World Wide Web, typically downloading pages and other content for indexing. Web crawlers are also used to collect data from the web for market research and other business purposes.
The first web crawler was developed at the Massachusetts Institute of Technology by Matthew Gray in 1993. The crawler, named World Wide Web Wanderer, was designed to index the web for the NSF-funded World Wide Web project. [source]
Since then, web crawlers have become an important part of the web ecosystem. Crawlers are used by search engines, online retailers, and other businesses to collect data about the web and to build indexes of the content on the web.
There are a number of different types of web crawlers, but all of them share a few common features. Crawlers typically:
- Follow links from page to page, downloading and indexing the content on each page,
- Crawl slowly so as not to overwhelm the servers they are accessing,
- Use algorithms to decide which pages to crawl and which to ignore.
Crawlers can be configured to follow different sets of rules, depending on the needs of the crawler’s owner. For example, a crawler may be configured to follow all links on a page or to follow only certain types of links. Crawlers may also be configured to exclude certain types of content, such as images or videos.
There is no one “right” way to crawl the web, and different crawlers may have different strengths and weaknesses. Some crawlers are better at finding new pages, while others are better at indexing the content on pages they find. Some crawlers are better at crawling fast, while others are more careful about not overwhelming the servers they are accessing.
Crawlers are also used for other purposes, such as data mining and market research. Crawlers can be used to collect data about website visitors, including information about the pages they visit and the search terms they use. Crawlers can also be used to collect data about online sales, including product data and customer demographics.