Learn about free software libraries, packages, and SDKs that can get your web crawling journey started in no time.
The amount of data online hit 40 zettabytes in 2020. And with one zettabyte being equal to a billion terabytes, that is a lot of information at our disposal. While organizations and companies need to harness big data for insights into their markets, it is estimated that over 80 percent of this data is unstructured. But to be able to use this data effectively, it needs to be in a machine-readable format, so you need structured data.
Other than internal statistics, research, and databases of organizations, an incredible source of data is the web itself. The extraction of online data can either go by the term web scraping or web crawling. What’s the difference? A web crawler is often used by search engines, which crawl websites, look for links, and pages, then extract their content in a relatively indiscriminate manner. A web scraper, on the other hand, extracts information from a website based on a certain script, which is often tailored to a specific website and its corresponding elements. It’s great for transforming unstructured data into structured databases of information. To learn more about the differences between the two, have a read through our web crawling vs. web scraping blog post.
What is a web crawler used for?
Web crawlers help you index web pages, locate content, and gather data from public websites. Crawlers also look at URL links within a website and try to work out a schema for how these pages are interconnected. This crawling helps you analyze the website from a wider perspective and makes it easier for online tools such as search engines to display a simplified version of it in the form of search results.
What are open-source web crawlers?
When software or an API is open-source, its code is available to the general public for free. It's even possible to modify and optimize the code to suit your needs. The same goes for open source web crawlers: you can download or use them without paying anything and fine-tune them based on your use case.
Is it legal to crawl a website?
Crawlers or scrapers are tools to automate data extraction at scale. So, for example, instead of manually copying a product list of an e-shop, a crawler does it for you. It is legal, but you still need to be careful not to accumulate sensitive data such as personal information or copyrighted content.
Top 11 open-source web crawlers
Now that we know what web crawlers are and what they’re used for, let's explore some of the most popular open-source crawling tools available online:
Language: Python | Github: 43.5k stars | link
The most popular web crawling tool found online, also suitable for large-scale web scraping. And, being asynchronous, requests aren’t made one at a time, but in parallel, resulting in very efficient crawling.
Language: Python | Github: 15.4k stars | link
A powerful open-source spider (crawler) package written in Python. Compared to other crawling tools, Pyspider not only provides data extraction functionality but also a script editor, task monitor, project manager, and result viewer.
Language: Java | Github: 14,4k stars | link
A scalable crawler framework to help simplify the development of a crawler. It covers the entire life cycle of a crawler, from downloading, URL management to content extraction.
4. Node Crawler
A popular and powerful package for crawling websites with the Node.js platform. It runs based on Cheerio and comes with many options to customize the way you crawl or scrape the web, including limiting the number of requests and time taken between them.
5. Beautiful Soup
Language: Python | Github: n/a | link
Beautiful Soup is an open-source Python library used for parsing HTML and XML documents. After creating a parse tree, extracting data from the web is much easier. Although not as speedy as Scrapy, its mainly praised for its ease of use and community support for when issues arise.
Language: Ruby | Github: 5.9k stars | link
Like Beautiful Soup, Nokogiri is also great at parsing HTML and XML documents, but via the programming language Ruby, which is great for beginners in web development. Nokogiri relies on native parsers such as C’s Lixml2 and Java’s xerces.
Language: Java | Github: 4.3k stars | link
An open-source Java web crawler with a simple interface to crawl the web. Its advantages include the ability to build a multi-threaded crawler, but it falls back on excessive memory use.
Language: Python | Github: 3.9k stars | link
A Python library used for parsing websites, based on the aforementioned BeautifulSoup, with inspiration coming from the Mechanize library. It’s great for storing cookies, and following redirects, hyperlinks, and forms on a website.
9. Apify SDK
10. Apache Nutch
Language: Java | Github: 2.4k stars | link
An extensible open-source web crawler often used in fields like data analysis. It can fetch content through protocols such as HTTPS, HTTP, or FTP and extract textual information from documents formats like HTML, PDF, RSS, and ATOM.
Language: Java | Github: 2.2k stars | link
Written by the Internet Archive, Heritrix is an open-source crawler designed mainly for web archiving. It collects extensive information, such as domains, exact site host, and URI patterns, but needs a little tuning when handling bigger tasks.
Last, but not least…
So, no need to overthink it, go ahead and try it for free!