Web scraping, the automated extraction of data from websites, has become an essential tool for businesses looking to gather valuable information at scale. Whether for price monitoring, lead generation, market research or something else, web scraping empowers organizations to collect the data they need to make informed decisions and stay competitive.
However, the practice of web scraping is not without its challenges. Many websites employ various techniques to detect and block scrapers, from IP tracking to CAPTCHA prompts to rate limiting and more. As web scraping grows in popularity, companies must get smarter about how they build and run their web scrapers to ensure maximum success and minimum interruptions.
In this ultimate guide, we‘ll dive into 10+ web scraping best practices that will help you scrape websites effectively while flying under the radar. From basic tips to advanced techniques and recommendations on top proxy providers, you‘ll learn everything you need to know to take your web scraping to the next level in 2023. Let‘s get started!
Why Websites Block Web Scrapers
Before we jump into web scraping best practices, it‘s important to understand why websites attempt to detect and block web scrapers in the first place. There are a few key reasons:
- To prevent server overload – Scrapers can make many requests in a short period of time, putting strain on web servers and potentially slowing down or crashing websites.
- To protect intellectual property and content – Some companies want to prevent competitors from easily copying their data and using it for their own gain. Blocking scrapers helps safeguard this valuable content.
- To stop price scraping – Many ecommerce websites don‘t want their prices to be routinely scraped and undercut by rivals, so they block suspicious scraping activity.
- To preserve a good user experience – An influx of bot traffic can hamper website performance for real human visitors. Blocking web scrapers helps maintain a smooth user experience.
- To prevent spam and abuse – Malicious bots can scrape websites to harvest emails and personal information for spam. Blocking them protects user privacy and cuts down on spam.
So while web scraping itself is not illegal, many websites are incentivized to prohibit it for the above reasons. That‘s what makes it tricky and why following web scraping best practices is so critical for success.
10+ Web Scraping Best Practices
Now that you know the "why" behind anti-scraping measures, let‘s look at 10+ best practices and techniques you can use to scrape websites sustainably and effectively:
1. Respect Robots.txt
Robots.txt is a file that tells web crawlers which pages on a website they are allowed to scrape. It‘s essentially a set of rules put forth by the website owner. While it‘s not legally binding, it‘s still good etiquette to follow and respect robots.txt by configuring your web scraper accordingly.
Be sure to program your crawler to check for this file and obey the instructions. Blatantly ignoring robots.txt is not only impolite, but will likely get your scraper blocked sooner. Tools like Screaming Frog make it easy to analyze robots.txt files.
2. Read the Terms of Service
In addition to robots.txt, most websites have a terms of service (ToS) that governs how their content and services may be used. Some may explicitly prohibit any form of web scraping.
While these terms are difficult to enforce from a legal perspective, it‘s advisable to read and adhere to them as much as possible. At the very least, understand what the rules are and weigh the risks carefully before scraping websites that forbid it. Getting sued is never fun.
3. Make Requests Through Proxies
The #1 way websites identify and block web scrapers is by IP address. If they see the same IP making a high volume of requests in a short timeframe, it raises a red flag.
That‘s why one of the most important web scraping best practices is to route your requests through proxies. A proxy acts as an intermediary between your scraper and the target website, masking your true IP address.
There are a few types of proxies you can use:
- Datacenter proxies – Fast and cheap, but more easily detected
- Residential proxies – Sourced from real user devices, harder to block but pricier
- ISP proxies – Combine speed and authority of datacenter proxies with legitimacy of residential IPs
In general, residential proxies are the preferred choice for large scale web scraping. Look for providers that offer a huge pool of IPs (in the millions) and automatic rotation.
Some of the top proxy services we recommend are:
- Bright Data – Largest proxy network with over 72M residential IPs
- IPRoyal – Ethically-sourced residential proxies with flexible plans
- Proxy-Seller – Budget-friendly residential and ISP proxies
- SOAX – Quality mobile and desktop residential proxies
- Smartproxy – Plenty of locations and strong scraping performance
- Proxy-Cheap – Affordable backconnect residential proxies
- HydraProxy – Excellent dedicated proxies for sneakers/retail
4. Rotate User Agents
Beyond IP address, websites can use your user agent to identify and block web scrapers. The user agent is a string that tells websites what type of device and browser you are using.
Most web scraping tools have default user agents that are easy for websites to blacklist. So another key best practice is user agent spoofing. Use a pool of common user agent strings and rotate them with each request you make to avoid detection.
Here‘s an example in Python using the requests library:
import requests
from random import choice
user_agent_list = [
#Chrome
‘Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.113 Safari/537.36‘,
‘Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.90 Safari/537.36‘,
#Firefox
‘Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:66.0) Gecko/20100101 Firefox/66.0‘,
‘Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:66.0) Gecko/20100101 Firefox/66.0‘,
]
url = ‘https://www.example.com‘
user_agent = choice(user_agent_list)
headers = {‘User-Agent‘: user_agent}
response = requests.get(url, headers=headers)Make sure to populate your user agent list with browsers that are up-to-date. You can find extensive, ready-made lists of user agents on GitHub.
5. Introduce Delays Between Requests
One of the most obvious differences between human and scraper behavior is timing. A real user clicks around at a relatively slow, random pace, while scrapers make requests lightning fast at fixed intervals.
As a general rule of thumb, you should limit your scraper to 1 request every 10-15 seconds. Introduce delays using functions like time.sleep() in Python to space out your requests in a more natural way. You can even randomize the length of delay between a min and max value.
Some sites may allow a higher rate limit than this. Use trial and error to determine what the acceptable threshold is for your specific target. The goal is to find a "Goldilocks" place – scraping as quickly as possible without getting blocked.
6. Improve Your Bot‘s Fingerprint
More websites are starting to use browser fingerprinting to identify scrapers. This is a technique where unique attributes about a user‘s browser and device configuration are detected and combined to create an identifier.
Websites can look at things like screen size, installed plugins, time zone, and more to determine whether a visitor is likely a bot or human. That means simply rotating IPs and user agents may not be enough to avoid blocks.
Some tips to make your scraper seem more human:
- Use common screen resolutions, like 1920×1080
- Set an appropriate time zone for the location of your proxies
- Ensure your scraper has standard fonts and plugins installed
- Change your Tor control circuit occasionally, if using Tor
- Clear cookies and browser cache between sessions
Essentially, try to match your scraper fingerprint to typical user configurations in your target market. Avoid using default settings for headless browsers, as these can be huge red flags.
7. Use Headless Browsers for Dynamic Sites
For JavaScript-rendered websites and single page apps, basic HTTP requests won‘t cut it. The content loads dynamically after the page is rendered in the browser. Your garden variety scraper won‘t be able to "see" this.
In these cases, you‘ll need to use a headless browser like Puppeteer or Selenium. These tools run an actual browser instance, allowing your scraper to fully load and interact with dynamic pages just like a human would.
Headless browsers come at a cost of added complexity and slower performance. While they are essential for some sites, avoid using them unnecessarily when simple HTTP requests will suffice. A good rule of thumb is to first try making a standard GET request to the target URL and inspect the response HTML. If key content is missing, then it‘s probably being rendered on the client side.
8. Leverage APIs Whenever Possible
Whenever possible, the best web scraping practice is actually to not scrape at all! Many websites offer public APIs that allow you to access their data in a structured format. Using an API is almost always faster and more reliable than building a web scraper from scratch.
Before embarking on a scraping project, always check whether the target website has an API available. Look for documentation on their site or try appending ‘/api‘ to the URL to see if anything is exposed.
For sites without a formal API, inspect the network traffic to see if you can reverse engineer where the data is coming from. Many times you will find hidden API endpoints that return nicely structured JSON, saving you the trouble of parsing messy HTML.
9. Handle Cookies and Sessions Properly
Some websites require you to login or maintain an active session to access data. That means your scraper needs to be able to handle cookies correctly to avoid getting blocked.
Use your browser‘s developer tools to inspect the HTTP headers and look for cookies that are set after logging in. Configure your scraper to store and send these same cookies with each request to authenticated pages.
Also be on the lookout for session timeouts. Sessions usually expire after a period of inactivity, which can cause your scraper to suddenly start failing. Build retry logic to re-authenticate when this happens.
10. Regularly Monitor and Maintain Scrapers
Web scraping is not a set-it-and-forget-it affair. Websites change frequently, which means your scrapers need to adapt as well. A small tweak to the site‘s HTML can completely break your parsing logic if you‘re not careful.
Combat this by regularly monitoring your scrapers and setting up alerts to notify you of any failures. Keep a close eye on metrics like success rate, response time, and error rate.
It‘s also good practice to build unit tests for your scraper that verify the expected data is being extracted correctly. Run these tests on a schedule to proactively catch any breaks.
Finally, make maintaining and updating your scrapers a regular habit. Schedule time to review your scrapers, adapt to any website changes, and make improvements. Like any critical infrastructure, web scrapers require diligence and upkeep.
Putting It All Together
Building a robust, undetectable web scraper is equal parts art and science. There is no magic bullet to completely avoid getting blocked, but by implementing as many of the above web scraping best practices as you can, you‘ll be well on your way to more successful and sustainable scraping.
Remember to always respect website owners and practice good scraping etiquette. Use the tips in this guide to extract the public web data you need without unduly burdening servers or damaging the user experience for others.
Monitor your scrapers closely, use quality proxies, and keep evolving your techniques as websites get smarter. With the right approach, web scraping can be an invaluable weapon in your data arsenal.
Happy scraping!
