Web scraping can feel like the wild west – a lawless landscape of grabbing data however you want. But in reality, effective web scraping involves carefully following best practices to get data legally and sustainably.
In this comprehensive 3000+ word guide, we‘ll cover 8 key strategies any scraper engineer should know. Master these web scraping fundamentals and seamlessly extract the data your business needs.
Contents
- Review Robots.txt and Terms of Service
- Use an Appropriate Crawl Rate
- Rotate Proxies and Randomize User Agents
- Solve CAPTCHAs with Specialized Services
- Migrate to Official APIs When Possible
- Mimic Natural Human Behavior
- Monitor for Site Changes
- Use a Robust Scraping Framework
- Scraping Legally and Ethically
- Scraping Best Practices Key Takeaways
Review Robots.txt and Terms of Service
Before writing a single line of code, checking two key documents is an absolute must:
Robots.txt – This file tells automated scrapers which pages they can and can‘t access. It may limit the crawl rate or block parts of the site entirely.
Terms of Service (ToS) – The ToS lays out rules all users agree to when visiting the site. It may specifically prohibit scrapers or certain usage of the data.
Failure to follow these guidelines can lead to legal trouble or permanent access blocks. So reviewing them should be the first step for any web scraping project.
To check a site‘s robots.txt file, simply visit:
www.example.com/robots.txtThe Terms of Service is typically linked at the bottom of the website.
For example, Yelp‘s robots.txt [1] specifies a crawl delay of up to 5 seconds per domain. Their ToS [2] clarifies the data can‘t be used to harm consumers, such as exposing private information.
Understanding these ground rules prevents wasted effort scraping data you can‘t use. It also shows respect to the site by scraping responsibly within their defined bounds.
Use an Appropriate Crawl Rate
Scraping too aggressively triggers anti-bot defenses and access blocks. Crawling politely is crucial for ongoing success.
Here are some key crawl rate guidelines:
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Add delays between requests – 1-5+ seconds per request is typically safe. Use random delays to appear more human.
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Limit simultaneous connections – 10 concurrent connections per domain is reasonable for most small to medium sites.
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Scrape during off-peak hours – If the site gets heavy daytime traffic, scrape at night when server load is lighter.
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Obey robots.txt limits – Stay under any crawl rate limits defined in the site‘s robots.txt file.
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Watch for 403 or 429 errors – These responses indicate you‘re sending too many requests too quickly.
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Scale up gradually – Start with simple tests to gauge a site‘s capabilities before heavy scraping.
Throttling your scraper is vital for flying under the radar. According to Imperva [3], over 25% of sites now block scrapers entirely. Excessive load is one of the top reasons.
The best practice is to ramp up slowly, monitor for issues, and stay conservative with your crawl rate. Polite scraping keeps data flowing while avoiding problems.
Rotate Proxies and Randomize User Agents
Websites often block scrapers by blacklisting their IP addresses after seeing too many requests. User agents can also be tracked to identify bots.
To avoid this detection, you should:
Rotate proxy IP addresses – Each request should use a different proxy IP to mask your identity. Avoid reusing the same IPs which are easier to blacklist.
Randomize user agents – Use a different, real user agent string for every request. Maintain a large up-to-date list of mobile and desktop user agents to randomize.
Avoid patterns – Don‘t reuse the same IP and user agent combinations. This allows sites to connect the dots across your different proxies.
With regularly rotating proxies and user agents, your scraper appears as a stream of totally distinct users. The site can‘t easily isolate the traffic as coming from a single bot.
Tools like ProxyRack [4] and Smartproxy [5] provide cloud-based proxy rotation APIs ideal for scrapers. Integrating them takes just a few lines of code.
The extra effort to "mask your scent" pays off by keeping your scraper undetected. Rotate often for long-term, uninterrupted data access.
Solve CAPTCHAs with Specialized Services
CAPTCHAs are a common obstacle designed explicitly to thwart bots. But there are now services that can automatically solve CAPTCHAs using machine learning techniques and human teams.
Top options include:
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Anti-Captcha – Over 2 billion CAPTCHAs solved with high accuracy [6]
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Death by Captcha – CAPTCHA solving API starting at $1.39 per 1000 CAPTCHAs [7]
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2Captcha – Solves CAPTCHAs for as low as $0.70 per 1000 [8]
These services provide APIs to send and receive the CAPTCHA challenges. Behind the scenes, they quickly solve the CAPTCHAs so your bot can carry on scraping uninterrupted.
Solving services provide a reliable way to navigate past CAPTCHAs. However, overusing them may be considered Terms of Service abuse on some sites. Use judiciously when absolutely required.
Migrate to Official APIs When Possible
Many major sites like Google, Twitter and Facebook offer official APIs for accessing their data. These have defined rate limits and require authorization keys.
Although APIs may have usage limits, they provide a legal and sustainable path for getting data. Here are some key advantages:
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No blocks – APIs are sanctioned access points unlike scraping. No risk of bans.
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Structured data – Output returned in clean JSON rather than messy HTML.
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Cost savings – No proxies needed and less server overhead than browsers.
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Better compliance – Pick only the permitted data fields unlike scraping everything.
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Documentation – Details for proper usage and integration readily available.
Check if the target site has an API covering some or all of your data needs. If so, migrating away from web scraping to the API may be warranted despite extra integration work.
Mimic Natural Human Behavior
Bots getting blocked isn‘t always due to scraping speed – it‘s the robotic nature of how they operate. Mimicking human quirks is key for stealth.
Examples of human-like behavior:
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Add random scrolling – Scroll pages a variable amount before clicking items, don‘t instantly snap between elements.
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Vary actions timing – Don‘t instantly click buttons or links, include random delays.
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Use a headless browser – Headless Chrome and Firefox perform dynamic JS rendering just like a real browser.
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Hover randomly – Move mouse across elements and delay clicks to appear more human.
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Avoid repetition – If scraping many item pages, don‘t follow the exact same steps each time.
According to Botometer research [9], mimicry of human traits like mouse movements evades even advanced bot detection algorithms. The more natural randomness you integrate, the stealthier your scraper.
Monitor for Site Changes
Websites evolve frequently – new bot defenses get added, site layouts change, JS rendering updates, etc. These changes can wreak havoc on your existing scrapers.
To avoid surprise failures, you should:
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Schedule regular regression testing – Run end-to-end tests to check for broken flows or missing data.
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Inspect templates – Periodically examine sampled HTML output for altered selectors or markup.
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Log errors – Debugging issues as they occur prevents minor changes from accumulating into major failures.
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Version control – Track changes made to your scraper code to aid debugging flow issues.
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Automate where possible – Use diff tools and visual regression testing to automatically catch changes.
With vigilant monitoring, you can rapidly respond to changes instead of being left scrambling. Don‘t "set and forget" your scraper – the maintenance investment pays off.
Use a Robust Scraping Framework
Writing one-off scripts leads to scrapers that fail at the slightest site change or bot block. For resilient scraping, a robust framework like the following is highly recommended:
Popular Scraping Frameworks
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Scrapy – Python-based, handles proxies/rotation, exports to JSON/CSV, 1000s of libraries [10].
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Puppeteer – Headless Chrome browser API with stealth options, can execute JS [11].
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Playwright – Browser automation for Chrome, Firefox and more, auto-waits for elements [12].
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Cheerio – Fast jQuery-style HTML parsing and selection for Node.js [13].
These tools provide advanced functionality like proxies and browsers, automatic retrying and navigation, caching, built-in throttling, and extensibility.
While frameworks have a learning curve, they encourage resilient design instead of flimsy one-off scripts. The long-term benefits outweigh the upfront cost.
Scraping Legally and Ethically
Mastering the technical side is only half the story. Equally important is scraping responsibly by following ethics and site owner guidance:
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Only scrape data you have rights to use – Public data isn‘t necessarily free for taking without permission.
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De-identify personal information – Remove emails, usernames or other personal data that could compromise privacy if exposed.
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Minimize scraping impact – Be judicious in your data needs, don‘t make unreasonable requests of smaller sites.
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Provide attribution if republishing scraped content per licensing terms.
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Be transparent if contacted by the site owner – concealment only raises suspicion.
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Fix issues promptly if informed of problems caused by your scraper.
Scraping sustainably means thinking beyond what data you can grab, to what you should grab. Keep ethics at the forefront and problems are avoided.
Scraping Best Practices Key Takeaways
Those are 8 of the most important fundamentals to succeed with web scraping:
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Check robots.txt and Terms before scraping
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Use a modest crawl rate and scale gradually
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Rotate proxies and randomized user agents
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Solve CAPTCHAs with specialized services
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Migrate to official APIs when available
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Closely mimic human browsing behavior
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Continuously monitor sites for changes causing breaks
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Use a robust framework for resilient scraping
Additionally, always respect site owner guidance, scrape ethically, and stay transparent.
Mastering these best practices separates scrapers that get blocked from those that securely gather data over the long-haul. Keep them in mind and your scraper will exceed expectations.
Scraping opens valuable data pipelines. With responsible design choices, you can extract information at scale without crossing ethical lines or causing disruptions.
Happy scraping! May your data flows stay smooth and plentiful.
