Web Crawling vs Web Scraping

The two differ in their goal and their output: a crawler answers "which pages exist?", a scraper answers "what does each page say?".

Web crawling is the automated discovery of web pages. A crawler starts from seed URLs, downloads each page, extracts its links and adds the new ones to a queue, repeating until it has covered its scope. It keeps a record of what it has seen so it never fetches a page twice, and it checks robots.txt before fetching. The details, with crawler types and examples, are in what is a web crawler.

Web scraping is the automated extraction of data from web pages. A scraper requests a page, renders it in a browser if the content needs JavaScript, finds each field with a CSS selector or XPath, cleans the values and stores them as rows. It does not need to discover anything: it can work on a fixed list of URLs or a single page. For the full explainer, see what web scraping is.

In practice, most scraping projects contain a small crawler. The usual pipeline:

The Scrapy spider below does both jobs on books.toscrape.com, a public sandbox built for scraping practice. Each page is scraped for titles and prices, and the "next" link is crawled to reach the following page. Replace <login> and <password> with your ProxyField credentials.

# pip install scrapy  ->  scrapy runspider books.py -O books.json
import scrapy

PROXY = "http://<login>-country-us-city-new_york:<password>@gate.proxyfield.io:7000"

class BooksSpider(scrapy.Spider):
    name = "books"

    async def start(self):
        yield scrapy.Request("https://books.toscrape.com/", meta={"proxy": PROXY})

    def parse(self, response):
        for book in response.css("article.product_pod"):        # scraping
            yield {"title": book.css("h3 a::attr(title)").get(),
                   "price": book.css("p.price_color::text").get()}
        next_page = response.css("li.next a::attr(href)").get()  # crawling
        if next_page:
            yield response.follow(next_page, self.parse, meta={"proxy": PROXY})

async def start() needs Scrapy 2.13 or later; older versions use start_requests(). For a crawl across a whole site, see how to crawl a website.

• Crawling alone when you need the list of pages itself: an SEO audit of broken links and redirects, a site map, an archive, or a search index.
• Scraping alone when you already know the URLs: a list of competitor product pages, your own keywords on a search engine, or one table on one page.
• Both when you need data from pages you have to find first: every product in a category, every job ad on a board, every article in a section.

If you have a sitemap, read it before crawling: it lists the URLs the site wants found and saves you most of the crawl.

A crawler, first: Googlebot discovers and downloads pages so Google can index them (Google Search Central: how Search works). Indexing then analyzes each page's content, which overlaps with scraping, but Google does not extract fields for a client the way a scraper does. In everyday use, "crawler" means the discovery bot and "scraper" means the data extractor.

"Crawler" and "spider" are the same thing, a bot that follows links to discover pages. Scrapy calls its crawl classes spiders even when they mostly scrape, which is one reason the terms blur. A "scraper" is the part that extracts data. A bot that only fetches a fixed list of URLs and reads fields is a scraper without a crawler.

Both send many requests to one site, so the same rules apply to both:

• Respect robots.txt and the site's limits, and add a delay between requests to the same site.
• Scope the crawl, so you fetch only the pages you need.
• Spread requests over many IPs once the site starts to limit you. Rotating proxies give each request a new IP; a sticky session holds one IP for a multi-page flow.

A crawl tends to fetch more pages than a scrape, but it can keep them light, since it needs only the links; a scrape may need a browser to render the fields. Estimate proxy traffic as pages × average page size. ProxyField residential proxies work with Scrapy, Crawlee, Playwright and Python requests over HTTP, HTTPS and SOCKS5, with unlimited concurrent threads, and you pay per GB with no subscription. Traffic never expires, and all purchases are final. Whether a given crawl or scrape is allowed: is web scraping legal.