Differences of Web Scraping Vs Web Crawling Explained
Sometimes people can use the terms Web Scraping and Web Crawling interchangably, however, they actually refer two different things.
Web scraping is when a "scraper" visits a web page, and extracts the specific data it wants from the page, often storing it in a database for later use.
Web crawling, on the other hand, is when a crawler visits a website and navigates through the entire website looking for particular information (normally pages, URLs, and links) then indexing it.
In short, web scraping is about extracting data, whereas, web crawling is focused on discovery.
In this guide we will explain the differences between web scraping and web crawling, including giving your examples of both and how they are often used together.
- What Is Web Scraping?
- What Is Web Crawling?
- How Are Web Scraping & Web Crawling Different?
- Combining Web Scraping & Web Crawling
- Are Web Scraping & Web Crawling Legal?
What Is Web Scraping?
Web scraping, also known as screen scraping or web data extraction, is the process of requesting data (web page, API response, etc.) from a website and extracting the specific data you want.
Typically, a web scraper is feed a list of URLs of web pages it needs to extract data from, and it systematically goes through each URL in the list requesting the web page from the website then extracting and storing the data it wants.
Web scraping enables the automated collection of web data at scale. Web scrapers can be configured to scrape data from a single web page or from millions of web pages every single day.
Common examples of web scraping include:
- Product Monitoring: A web scraper monitors a list of products every day on a e-commerce stores website so that someone can track the price of competitor products.
- Lead Generation: A web scraper can be designed to extract names and email addresses from websites so that sales teams can conduct email outreach.
- Social Media Monitoring: A web scraper can scrape profile data from social media sites like Twitter, Instagram or TickTok, so that the data can be used to track the growth and activity of social media accounts.
The use cases for web scraping are numerous and varying, as result a lot of companies rely on web scraped data to make more informed decisions or build their products.
What is Web Crawling?
Web crawling on the other hand is focused on data discovery and indexing. Here instead of extracting data from the page, a web crawler will be designed to go to a website and then systematically visit every page on the website looking for particular types of information. Usually with the goal of indexing all the pages and links.
Web crawling enables the automated mapping of all the data on a website so that it is easier to find for other systems and users. The best example of web crawling is search engines.
Search engines like Google, Bing and DuckDuckGo, build web crawlers who's purpose is to visit and map every website on the internet and determine what each web page is about and what keywords should it rank for.
How Are Web Scraping & Web Crawling Different?
There are a number of differences between web scraping and web crawling:
Difference #1: Purpose
Web scraping focuses on extracting data (product data, email addresses, etc.) from web pages so it can be used in other systems.
Whereas web crawling is focused on finding and mapping specific information on websites (or the entire internet) so that it is easier for other systems to find the information they are looking for when they need it.
With web scraping you know extactly what web pages you want to extract data from, whereas with web crawling you just know the website you want to crawl but have little to no idea about pages that website actually contains.
Difference #2: Data They Output
You can more clearly see the differences between web scraping and web crawling from the data they output.
Here is the typical output of a web scraper designed to extract product data from a e-commerce product page:
"name": "Product name",
"brand": "product brand",
"description": "product description",
In comparison, a web crawler will typically return a list of URLs for the pages it has discovered on the target website:
Difference #3: How They Identify Themselves
Typically, websites don't want the data on their website scraped so web scraper have to use a number of techniques to hide their real identity:
- Use proxies to hide their IP address
- Fake user-agents and browser fingerprints to look like a real browser
- Ignore the websites robots.txt file and/or terms & conditions.
In contrast, it is more common for websites to approve of their websites being crawled and indexed as it often helps their content to be discovered:
- Web crawlers like search engines, clearly identify their crawlers to the websites so they can be allowed to crawl the website.
- In the case of search engine crawlers, websites encourage web crawlers and make it easier for them to crawl their websites by providing sitemaps, etc.
Combining Web Scraping & Web Crawling
The reason that a lot of people get mixed up by the difference between web scraping and web crawling is because it is quite common for web scrapers and web crawlers to be used together.
For example: To scrape data from thousands of product page you first need the URL of the pages you want to scrape data from. However, how do you get the list of product page URLs to feed to your web scraper?
You could manually create a list of product page URLs you want to scrape which would be very time consuming, or you could use a web crawler to find all the target pages on the website and then feed them to your web scraper to extract the data from them.
This is a common pracitice amongst developers who need to build large scale web scraping systems.
The build a web crawler to discover pages on a website that they want to scrape. Then have other web scrapers visit those pages and extract the data they need.
Are Web Scraping & Web Crawling Legal?
This is a legal grey area and it really depends on what you are scraping/crawling, does the website want you to do it, and what do you do with the data.
In short, both web scraping and web crawling are legal if you are scraping/crawling publically available data (i.e. don't need to login) and you are not breaching any copyright or personal information regulations (like GDPR) with the data you extract.
If you are scraping/crawling behind a websites login, then you explicitedly agreed to the websites terms & conditions when you created the account which may prohibit web scraping or crawling of them website.
More Web Scraping Guides
This was a overview of the differences between web scraping and web crawling.
If you would like to learn more about web scraping in general, then be sure to check out The Web Scraping Playbook, or check out one of our more in-depth guides: