Anti bot measures

Web Crawling: Top 6 Most Common Anti-Bot Measures

The evolution of technology has given rise to multiple sources of useful data that, when harnessed, has proven beneficial to businesses. With the emergence of machine learning (ML) and artificial intelligence as well as powerful data analysis software, the data collected can be analyzed and distilled to establish inconsistencies, relationships, patterns, trends, and irregularities. But everything, save for the data generation, begins with data collection.

Web crawling is one of the valuable techniques for collecting data. It is carried out automatically by web crawlers. However, the activity of these crawlers is limited by anti-bot measures integrated into websites to safeguard the information therein or to protect the servers by limiting the number of requests they can receive. This article will discuss what a web crawler is, what web crawling entails, and the top 6 most common anti-bot measures. Let’s get into it.

What is a Web Crawler?

Also referred to as a spider, a web crawler is a bot that clicks on and subsequently follows URLs embedded in web pages as href attributes/links to discover new web pages and content. Next, the spider collects all the information stored in the HTML code file. Then, it archives the extracted data for future retrieval in a process known as indexing. One of the leading experts wrote an article about web crawlers, make sure to check it.

While each of these steps has a different name, they are collectively referred to as web crawling. Businesses can benefit from the functions of web crawlers. For instance, they can use spiders to discover websites containing pricing or product information from their competitors, which can help them develop competitive pricing. As well, spiders can aid in the brand and reputation monitoring.

That said, web crawling is not always smooth as it is impacted by anti-bot techniques. In this article, we will detail the top 6 most common anti-bot measures.

Top 6 Most Common Anti-Bot Measures

Usually, web developers integrate anti-crawling techniques into the everyday functions of websites to deter any automated data extraction efforts. The measures also protect the servers from distributed denial of service (DDoS) attacks. The most common anti-bot measures include:

  2. IP blocking
  3. User-Agents (UA)
  4. Sign-in/login requirements
  5. Honeypot traps
  6. Headers

1.     CAPTCHAs

Short for Completely Automated Public Turing test to tell Computers and Humans Apart, CAPTCHAs are puzzles or challenge-like tests used to differentiate human users from bots. Mostly, these puzzles are displayed whenever web servers discover unusual traffic from a single IP address.

2.     IP Blocking

Usually, web crawlers send numerous HTTP requests as they have to follow every URL they come across (as long as they are permitted to do so as per the instructions in the robots.txt file). In large-scale crawling applications, this means that the requests outnumber the natural number a human user would send.

If unchecked, especially if the bots are on a malicious mission, the requests could crash a website. To protect against this, websites and their servers/hosts monitor the number of requests from each IP address, only blocking those from which an unusual number of requests originate.

3.     User-Agents

A User-Agent (UA) is a piece of text sent by a web client (browser). This text contains information on the type of browser/web-based application, operating system, and version used by the originator of the HTTP requests. Normally, a bot would not obey the UA requirements. In such a case, the server will block requests.

4.     Sign-in/Login Requirements

Ethical web crawlers do not crawl web pages hidden behind a login/sign-in landing page. This is because sensitive information could be stored on the other side of these pages. In this regard, sign-in/login pages are another anti-bot technique. They enable web servers to detect bots, particularly when login attempts fail.

5.     Honeypot Traps

A honeypot trap is invisible to human users, and can be detected by bots such as web crawlers. As an anti-bot measure, honeypot traps help servers identify bots (as only bots can click the invisible links). Next, they block the bots.

6.     Header

A header provides additional information about the user or resource being requested. It is sent alongside an HTTP request. There are different types of headers, including referrer headers and UAs. A referrer is a header that describes the site from which you get redirected. Traffic originating from a known website, such as a search engine, is trusted by web servers. Else, the requests may be blocked.

With the increased use of anti-bot measures, web crawlers have emerged as a great and reliable tool to bypass the measures. Sophisticated web crawlers use headless browsers to go around the UA and header requirements. They also use proxy servers to help avoid CAPTCHAs and IP bans. However, while crawlers do the job, it is worth pointing out that a few malicious spiderbots also exist. It is, therefore, important to ensure you use a trusted crawler from a reliable service provider.


Data acquisition is a central pillar for businesses in the current data-driven era. With it, web crawling and web crawlers have emerged as valuable data collection tools. And with the evolution of technology that has given birth to anti-bot measures, sophisticated crawlers can bypass the anti-crawling techniques ethically.

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