Top 8 List of Open Source Web Crawlers Tools in 2021

WEB CRAWLER DEFINITION

Search Engine performs indexing of all web pages in their archive for returning the most relevant and best content-based results to the searched query. The underlying technique or algorithm that enables search engines to do that is called Web Crawling. 

How Does a Web Crawler Tool Work?

A Web Crawler is a computer program that works as an automated script crawl through the world wide web in a pre-encoded manner to perform data collection. Web crawlers record every website by crawling from one website to another. It also inches through every page of a website, further following the links on these pages until all pages have been read. The captured details of each page are then stored, indexed, and entries for them are created. The primary purpose of Web Crawler is to learn what every web page is about for enabling users to get more effective search results.

Indexing is performed based on various factors like: 

• The percentage of content matching to the user search query. 

• The number of times the content has been scrolled and shared. 

•  Quality of the content. 

• The number of times it has been referred. 

Importance of a Web Crawler

The amount of data on the internet rapidly increases every passing day, and 90% is unstructured. This data marks the importance of Web Crawler Tools, which navigates through the unstructured data and indexes it based on the factors mentioned above, enabling the search engines to have the most relevant quality results.

It also helps accelerate the SEO market and improve the ranking of web pages by pointing out loopholes like duplicate content, broken links, missing page titles, and other significant SEO-based problems. 

List of Web Crawlers Open-Source in 2021 

1. SCRAPY

Scrapy is a trendy open-source web crawling framework developed in python.

Its basic features include: 

•  Automated crawling with data processing and storage mechanisms 

•  Data extraction from webpages as well as APIs 

•  Search engine indexing 

Its powerful features include: 

• Selection and Extraction of data from HTML/XSS sources with extended CSS selectors and XPath expressions. 

•  Interactive shell console, which is very beneficial in the amending and debugging of crawlers.

•  Generation of feed exports in multiple formats like JSON, CSV, XML with backend storage also in multiple formats like FTP, S3, local filesystem. 

•  Auto-detection for broken encoding declarations 

•  Allows to patch in one's functionality using signals and defined APIs. 

•  Provides extensions and middleware for handling sessions, cookies, compression, authentication, caching, user-agent spoofing, crawl depth restriction, and more. 

•  telnet console that can hook into python console running inside scrapy to introspect and debug crawler. 

Advantages: 

•  Easily understandable and usable with its detailed documentation available

• Provides the option to amend new functionalities to the existing framework.

•  Abundance of resources and help available on it. 

•  Scrapper has a cloud environment, which does not utilize the end-point resources.

•  Fast performance with powerful features 

Disadvantages: 

•  The installation and setup process for scrapy is a bit complicated. 

•  Its installation varies for different operating systems. 

 Documentation: https://docs.scrapy.org/en/latest/ 

2. HERITRIX

Heritrix has been designed as the generic web crawling automated tool with an open option of integrating and patching various other functional components into it. With this, the crawler moves from performing generic crawling into incremental, evolutionary feature-rich crawling. It has been written in Java and has a web-based user interface. 

Basic features include: 

• It uses HTTP recursively for content collection, covering hundreds to thousands of independent websites in a single crawl run. 

•  As it crawls from one website to another, it collects domains, exact site host, configurable URI patterns. 

•  It uses breadth-first search and site-first scheduling to finish the site in progress first before starting a new one for processing URIs. 

•  All its significant components are highly extensible.

•  Storage location for logs, temporary files, archive files, and reports are settable. 

•  Allows setting the maximum download size for output files and time for crawling. o Allows setting of bandwidth usage, also the crawling threads at work. 

•  It provides politeness configuration for setting upper and lower bounds of time between requests, also allows setting lag between requests and prioritization to fulfill most recent requests. 

•  It provides the option of configuring inclusion and exclusion of its various filtering mechanisms, e.g., regular expressions, URI path depth.

Advantages: 

•  It provides the option of plugging and replacing components. 

•  Does not counteract robot.txt and meta robot tags. 

•  Provision of the web-based user interface. 

Disadvantages: 

•  It does not support multiple instances of crawling. 

•  The running of large crawls requires operator tuning within resource limits. 

•  It does not support revisits to the areas of interest as each crawl becomes independent. 

•  It has been officially tested just on Linux. 

•  It cannot detect failures and recover them during the crawling.

 Documentation: https://heritrix.readthedocs.io/en/latest/ 

3. MECHANICAL SOUP

Mechanical Soup is also a python-based library that automates website interactions imitating human behavior when using a web browser. 

Some of Mechanical soup basic features include: 

•  It automatically follows robots.txt. 

•  It automatically stores, sends cookies, follows redirects, and submits forms. It is incompatible with JavaScript. 

•  Its .browser module uses urllib2.OpenerDirector to open URLs on the internet. o It easily fills out HTML forms. 

•  It also automatically handles HTML. Equiv. 

•  It has .back() and .reload() methods this provides the facility to revisit certain interesting content. 

•  It provides other APIs like Requests for HTTP sessions and Beautifulsoup for document navigation.

Advantages: 

•  The website crawling process is faster. 

•  Since it simulates human behavior. 

•  It is easier to set up. 

•  It is compatible with CSS and XPath selectors. 

Disadvantages: 

• They do not fully duplicate browser functionality, particularly for client-side javascript.

Documentation: https://mechanicalsoup.readthedocs.io/en/stable/ 

4. PYSPIDER

PYSpider has been regarded as a robust web crawler open source developed in python. It has a distributed architecture with modules like fetcher, scheduler, and processor. 

Some of its basic features include: 

•  It has a powerful web-based User Interface with which scripts can be edited and an inbuilt dashboard that provides functionalities like task monitoring, project management, and results viewing and conveys which part is going wrong. 

•  Compatible with JavaScript and heavy AJAX websites. 

•  It can store data with supported databases like MYSQL, MongoDB, Redis, SQLite, and Elasticsearch.

•  With PYSpider, RabbitMQ, Beanstalk, and Redis can be used as message queues. 

Advantages: 

•  It provides robust scheduling control. 

•  It supports JavaScript-based website crawling. 

•  It provides many features, such as an understandable web interface to use and a different backend database. 

•  It provides support to databases like SQLite, MongoDB, and MYSQL. o It facilitates faster and easier to handle scraping. 

Disadvantages: 

•  Its deployment and setup are a bit difficult and time taking. 

Documentation: http://docs.pyspider.org/ 

5. PORTIA

Portia is the best visual scraping tool developed by scrapinghub that does not require any programming knowledge. So, it has been developed for nonprogrammers. It can be tried for free without installing anything by creating an account into scrapinghub. Upon signing up, one can use their hosted web-based version. 

Some of its basic features include: 

•  With Portia, a simple point and click system are followed for extraction of required data. The user actions such as scroll, click, wait are simulated upon recording for further similar data scraping from pages. 

•  It creates the structure of pages once they have been visited. 

•  It is efficient in crawling AJAX-powered websites. 

•  It is compatible with heavy JavaScript frameworks such as Backbone, Angular, and Ember. 

Advantages: 

•  It is compatible with CSS and XPath selectors. 

•  It supports storage data formats such as CSV, JSON, XML. 

•  It filters the page it visits. 

Disadvantages: 

•  Its crawling process is time-consuming compared to other open-source tools. 

•  It can navigate unnecessary pages and yielding unwanted results if it is not pointed to the targeted pages.

Documentation: https://portia.readthedocs.io/en/latest/index.html 

6. NODE CRAWLER

Node Crawler is a fast web crawler that is developed in NodeJS, which makes it quite popular since it helps crawl website nodejs. It is best suited for those who prefer coding in JavaScript. It is compatible with non-blocking asynchronous I/O, which ultimately supports crawler pipeline operations. It supports efficient crawler development by endorsing the selection of DOM, thereby no regular expressions allowed. 

Some of its basic features include: 

•  Server-side DOM and automatic jQuery insertion with cheerio and JSDOM.

•  It follows a priority queue of requests. 

•  It has forced UTF-8 mode to deal with charset detection and conversion. 

•  It is compatible with all its encoding newer versions. 

Advantages:

•  Prioritization can be set for different URLs. 

•  It allows the configuration of retries and resource size. 

•  Its installation is pretty simple. 

•  Its speed can be controlled. 

•  It supports CSS and XPath selectors. 

•  Available data formats include CSV, JSON, XML. 

Disadvantages: 

•  It has no promised support. 

Documentation: https://github.com/bda-research/node-crawler 

7. APACHE NUTCH

This web crawler is written in Apache Hadoop and is regarded as quite well established. 

Some of its basic features include: 

•  It operates in the form of batches, with various steps of crawling being done in a separate batch like a list of fetchable URLs, web page parsing, updating of data structures, and more. 

•  It has a modular architecture. 

•  It permits developers to develop plug-ins for data retrieval, querying, clustering, media-type parsing. 

•  It also allows custom implementations to an interface. Hence besides being pluggable and modular, it has an extensible interface as well. 

Advantages: 

•  It provides a pretty extensible infrastructure. 

•  Its development and extension process is very active, and also its community is very interactive.

•  It provides dynamic scalability using Hadoop. 

Documentation: https://wiki.apache.org/nutch/ 

8. SCREAMING FROG 

Screaming frog is a web crawler due to its functionalities regarded as an SEO spider. It helps in the improvement of a site SEO by performing auditing on the standard site SEO issues. Its free trial offers to crawl 500 URLs. Its paid version can crawl millions of URLs with the provided correct hardware, memory, and storage. It has both the option of saving the crawled data in RAM or to disk in the database.

Some of its powerful features are as follow: 

•  It can crawl through the website and find broken links and server errors. 

•  It can get into the redirection loops/chains and find temporary/permanent redirects. It can also submit redirected URLs for audit. 

•  It identifies short, missing, long, duplicated page titles and meta descriptions. 

•  Discover duplicated and low content on pages. 

•  It can collect data from a webpage using CSS, XPath, and regex. 

•  It can find URLs blocked by robots.txt. 

•  It can keep a record of last modified, change the frequency over URLs by creating XML Sitemaps, Image Sitemaps. 

•  It can be integrated with Google Analytics, Search Console, and PageSpeed Insight APIs to fetch performance data to get better knowhow about URLs. 

•  It can crawl JavaScript-rich websites as well. 

•  It can visualize a URL architecture with its internal linking. 

Advantages: 

•  It is a feature-rich crawler. 

•  Provides a visual view of core SEO site elements. 

•  Provides an insight into what search engines index pages. 

•  By revealing SEO site issues, it provides opportunities for site optimization. 

•  Provides a Tree view of the hierarchical structure of a site. 

Disadvantages: 

•  It is not cloud-based and uses end-point resources. 

•  It takes you to the waiting zone for larger websites. 

•  Its interface is not easily understandable by beginners. 

•  Large sites take up a considerable amount of resources. 

•  The free version is limited. 

Documentation: https://www.screamingfrog.co.uk/seo-spider/user-guide/

Sources: 

-  https://www.octoparse.com/ 

-  https://www.guru99.com/ 

-  https://betterprogramming.pub/ 

-  https://prowebscraper.com/ 

-  https://www.sciencedaily.com/ 

-  https://www.simplilearn.com/ 

-  https://research.aimultiple.com/ 

-  https://webcuratortool.readthedocs.io/ 

-  https://skemman.is/bitstream/1946/6073/1/iwaw05-sigurdsson.pdf

- https://pypi.org/project/MechanicalSoup/ 

-  https://www.programmersought.com/article/30703279147/ https://www.scrapehero.com/