Knowledge Base

How does crawling work?

16d ago | By: FDS

"Crawling" is a process in the field of web scraping where automated programs, also known as web crawlers or spiders, navigate the internet and extract data from websites. The crawler follows links from one page to the next to gather information. Here is a basic explanation of how the crawling process works:

Set Starting Point: The crawler needs a starting point or a home page from which it can begin. This can be a specific URL or a list of URLs.

Send HTTP Request: The crawler sends an HTTP request to the chosen URL to obtain the HTML code of the page. This code contains the structured content of the webpage.

Analyze HTML Code: After receiving the HTML code, the crawler analyzes it to identify relevant information, such as links to other pages, text content, metadata, or structural information.

Extract Links: The crawler extracts all found links on the current page and adds them to a list of URLs that still need to be visited.

Visit the Next Page: The crawler selects a link from the list and repeats the process for the next page. This step is repeated until either all pages have been visited or a predefined limit is reached.

Avoid Infinite Loops: To avoid infinite loops, crawlers usually perform checks to ensure that a page is not visited multiple times.

Data Storage: During the crawling process, the extracted data, such as texts, images, or metadata, is typically stored in a database or file.

Respect robots.txt File: Crawlers often respect the rules in a website's robots.txt file. This file provides instructions on which parts of a website are allowed to be crawled and which are not.

It's important to note that not all web crawlers are the same. Some are used by search engines like Google for indexing content, while others are developed for specific data scraping purposes. The use of web crawlers should be ethical and respect legal frameworks and website policies to avoid issues such as legal conflicts or excessive server load.

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