Web crawlers, also known as spiders, are an integral part of the search engine user experience. Without them, search engines as we know them would not exist. However, while web crawlers are commonly associated with search engines, they are also used in other use cases, such as online browsing. content aggregation sites.
Essentially, spiders are software that automatically discovers websites. But there is more to their functionality, which brings us to the question, what is a web crawler?
What is a crawler?
Each website whose link you click on a search engine results page (SERP) or online aggregation site is the product of the invisible work done by crawlers. Ideally, and as stated above, these bots or spiders discover websites and web pages. They do this in a thorough and sophisticated way by following the hyperlinks included in the web pages. Usually, websites contain links for ease of navigation – these hyperlinks direct users or crawlers to content that is part of the website or an external website.
How does a web crawler work?
Web crawlers use hyperlinks to discover web pages. They simply start with an array of known websites (URLs) from previous crawls or from web addresses provided by site owners. Then the spiders visit the sites and use the links included on the known web pages to discover new pages, either on the website or on external sites. They repeat this process again and again, but not after doing an integral thing.
When crawlers discover a new page, they crawl the content from the first line of the code file to the last. They collect this information, organize it by associating a URL to this data, and store/archive it in databases called indexes. For this reason, web crawling is also called indexing because it involves storing discovered pages and their content in indexes.
When organizing this data for a webpage, crawlers move on to the next webpage(s) by following the link(s) there. They repeat this process over and over again. Notably, web spiders discover billions of new web pages through this automated but repetitive process. And to ensure indexes are up-to-date, crawlers periodically repeat the entire web crawling process to discover newly created web pages or recently updated content.
What is an indexing robot used for?
A spider performs the following tasks:
- It discovers new web pages and their associated addresses/URLs
- A web crawler displays the webpage, crawls the content stored in each webpage and collects key data like all words, URL, meta description, recent site update date, etc.
- The spider organizes and stores key data from each webpage in an index to allow the search engine or online aggregator to retrieve this data later, presenting it on the SERP according to relevance.
In particular, by collecting key data such as words, the index can identify words that will help search engine users find web pages. These words, called keywords, are an integral part of search engine optimization (SEO).
Although web crawlers collect data from websites, their functionality should not be confused with that of web scrapers.
What is a web scraper?
A web scraper is a bot that gathers specific data from websites in what is known as web scraping or web data harvesting. Web scraping is a step-by-step process that starts with requests.
A web scraper sends requests to specific sites from which data should be extracted. The respective web servers respond by sending an HTML code file containing all the data for the web page(s). Then the scraper analyzes the data, then converting it from an unstructured format to a structured form that humans can understand. Finally, the web scraping tool uses the structured data for downloading as a CSV, spreadsheet, or JSON file.
Differences between a web crawler and a web scraper
|Web crawler||Web scraper|
|It is used for large scale applications||It is used for large and small scale applications.|
|A web crawler collects an indiscriminate amount of data which includes all words contained in a web page, URL, meta description, etc.||A web scraper only collects specific, predefined and tangible data|
|Data collected by a web crawler is stored in indexes and cannot be downloaded by humans||Data collected by a web scraper is available for download by humans|
|A web crawler never relies on the services of a web scraper||A web scraper can sometimes depend on the operation of a web crawler|
|The output of a web crawler is a list of URLs ranked by relevance and displayed on SERPs or aggregator sites||The output of a web scraper is a downloadable file containing a table with dozens of fields and entries|
A web crawler is an integral part of today’s internet age. It is at the heart of search engines as we know them. However, although this program collects data from web pages, it should not be confused with a web scraper, which collects specific information from a small group of websites.