The terms web crawling and web scraping are often used interchangeably as if they mean the same thing. But did you know there’s actually an important difference between the two?
If you want to crawl or scrape your way through the web, it’s essential that you know which of the two practices best suits your needs. Without knowing the difference, you might have unrealistic expectations or end up paying for the wrong type of tool. So how do web crawling and web scraping differ?
You’ll find out below. In this quick overview, we’ll explain both practices in a bit more detail and highlight the different potential uses of each of them. After reading this short article, you’ll know exactly whether you need to crawl or scrape.
What is web crawling?
Web crawling is the automated process during which web crawlers – robots, also referred to as spiders – crawl their way through online pages.
These robots are given one or more URLs (called the seeds) as a starting point, from where they start crawling their way through all the content on the given web page.
Once they encounter another URL on that page, they follow this link to its target destination, and the process repeats itself.
So how does this work from a technical perspective?
Well, it works by creating a robot (that is, writing a code) that in many ways mimics what your search engine does for you when you browse the web.
You see, the moment you click on a link or type a URL in the search bar, your browser sends a request to that server to gain permission to view the page. A web crawler does the same thing by sending an HTTP GET request to the server of the URL you’ve given the bot to crawl.
Your bot then continues to browse through the content on the page, very much like how you would scroll through that same content yourself.
Now at this stage, your bot is just browsing. But what it does from here determines whether your bot is a crawler or a scraper.
A web crawler will most likely copy the information they come across in a database, called an index, from where they can serve the information when someone would request it. This is how search engines and their indexes work, and this is why web crawlers are almost exclusively used by search engines like Google, Bing, and Yahoo.
Web scrapers, on the other hand, take it a step further.
What is web scraping?
Web scraping is very similar to web crawling. In fact, in most cases, web crawling (or a similar automated process) is the basis of web scraping.
You see, as the name suggests, web scraping refers to the process of bots scraping data from a web page. This scraping (also referred to as data harvesting) is what differentiates it from crawling, as crawling only indexes the information rather than extracting it.
Furthermore, whereas a crawler will continue to follow new URLs on pages to add to his index, practically ad infinitum, a scraper can target a more specific single page or part of a page.
From a technical perspective, a scraper will not just visit pages and index the information, but it will fetch and download this information, storing it in a database or other format (like a spreadsheet).
Before storing it, the scraper will parse the data, turning it from raw HTML into whatever type of presentation you choose.
Web crawling vs. web scraping
So what are some real-world examples of both web crawling and web scraping? Let’s have a quick look, so you can see what type of bot might be best for your needs.
Web crawling uses
Web crawlers are predominantly used by search engines. Bingbot, Baiduspider, and Googlebot are the best-known examples of such robots.
However, you can use a web crawler for your business as well (even if you don’t own a search engine). And that especially counts for people interested in search engine optimization (SEO).
You see, SEO is the practice of improving a website to increase that site’s visibility in the search engine results pages (SERPs) for relevant keywords.
Since search engines depend on web crawlers to order the SERPs, what better way to improve your site’s performance in those SERPs than getting a web crawler of your own?
Common SEO tools like Deepcrawl, Screaming Frog, and SEMrush are all technically just web crawlers mimicking the work of search engine crawlers.
By crawling your site like a search engine bot would, these tools help you identify your site’s performance as seen through the eye of a search engine bot. This, in turn, allows you to make site improvements accordingly.
Web scraping uses
Since web scraping is, as we’ve seen, a lot more targeted approach than web crawling, it opens the door for a lot more targeted uses as well.
Web scraping can help you analyze, monitor, and extract all sorts of data from virtually any place you wish. You can do so by using pre-created tools (which range from general web scrapers to something as specific as mimicking a Google autocomplete API) or building a web scraper from scratch. For instance, if you’re looking for a tool that allows you to scrape Google autocomplete suggestions data, SERPMaster is one of the best tools to use.
Some of the many possible uses of web scraping include:
- Competitive price monitoring (like Amazon)
- Real estate listings gathering
- Lead generation
- Social listening and opinion mining
- Product listings gathering
And these are just a few examples of the plethora of possibilities when it comes to using web scrapers for your business.