Web crawlers are the invisible workers of the internet. You may not see them, but they visit your website almost every day. These digital agents, often called spiders, bots, or indexers, collect and organize data from websites. This data then gets stored and used by search engines like Google and Bing to create search results.
Let us learn how web crawlers function, discover the most common crawlers you should know about, understand the risks from harmful bots, and find out how to manage them efficiently.
What Are Web Crawlers And How Do They Work
Web crawlers are automated scripts. They scan web pages, follow links, and gather content. This process is called crawling.
Search engines use crawlers to discover and index content, build searchable databases and help users find relevant results.
To understand the importance of maintaining a crawler list and managing bots effectively, you first need to know how web crawlers work. A web crawler, also known as a spider or bot, is an automated script or software application. Its job is to browse the internet and collect data from websites. This process is called crawling.
Crawlers are used by search engines like Google, Bing, and Yandex. They scan web pages, follow links, index content, and build massive searchable databases. These databases make it possible for you to get search results when you type something into Google.
How Crawlers Discover And Navigate Websites
The crawling process usually starts with a list of known web pages. These could be popular sites, pages from previous crawls, or pages submitted through sitemaps. The crawler visits these pages, scans their content, and looks for hyperlinks. It then adds those links to its list of pages to crawl next. This cycle repeats continuously.
Check what happens during crawling:
- Start with a seed URL (an initial page or a set of pages).
- Download the page content and parse the HTML.
- Extract all the links on that page.
- Follow the links to discover new pages.
- Repeat the process across the web.
Some crawlers use breadth-first crawling, which covers all the pages on one level before going deeper. Others use depth-first crawling, which follows one path down before backtracking.
Search Engine Crawlers vs Third-Party Bots
There are two broad types of crawlers you should know about: good bots and bad bots. Good bots, also known as legitimate crawlers, are operated by search engines like Google, Bing, and DuckDuckGo to index websites and gather information for search results. Let us learn about them a more detailed
Search Engine Crawlers
Search engine crawlers include bots like Googlebot, Bingbot, Baiduspider, and others. They are responsible for indexing your content so users can find your site in search engines. These crawlers follow guidelines in your robots.txt file and usually respect crawl delays and access rules.
Third-Party Bots
Third-party bots are often built by SEO tools, AI models, content scrapers, or competitive research tools. Some are helpful, like SemrushBot or AhrefsBot, which help site owners analyze SEO performance. Others, like price scrapers or spam bots, may access your site aggressively and cause problems.
Crawling Policies And Architecture Essentials
Web crawlers are designed to be polite and efficient. Most legitimate bots follow rules defined in your robots.txt file. This file tells crawlers which pages they can or cannot access. Here are some key principles for effective web crawling:
- Politeness: Good crawlers limit the number of requests to avoid overloading your server.
- Prioritization: Bots often prioritize high-quality or frequently updated content.
- Refresh rate: Some pages are crawled more often, especially if they change frequently or attract traffic.
- Respect for robots.txt: Reputable bots honor disallow rules and crawl delays. Malicious bots usually ignore them.
Crawler List: Most Common And Emerging Web Crawlers in 2025
Building and maintaining a crawler list helps you understand which bots are visiting your site. This list is also key to managing your server resources, securing your content, and keeping your analytics data clean. Let us learn about the most widely used crawlers and new bots that are emerging in 2025.
Top Search Engine Crawlers to Know
Search Engine Crawlers come from major search engines and are responsible for indexing your site for users worldwide. They are generally safe, follow crawling rules, and are vital for your SEO.
- Googlebot: This is Google’s main crawler. It has several versions, including Googlebot-Desktop, Googlebot-Mobile, Googlebot-Image, and others. Googlebot checks your pages, updates the index, and helps your content appear in Google Search.
- Bingbot: Microsoft’s Bingbot works similarly to Googlebot and indexes pages for Bing. It also supports Microsoft’s newer AI-driven services.
- Applebot: Applebot crawls the web to collect content for Apple services like Siri and Spotlight. It follows robots.txt and supports Apple’s privacy standards.
- Baiduspider: This bot is from the Baidu search engine, which is dominant in China. If you are targeting a Chinese audience, allow this crawler access.
- YandexBot and DuckDuckBot: These bots come from Yandex (Russia) and DuckDuckGo, respectively. Both are known to respect robots.txt and are part of the trusted crawler community.
AI and Platform-Specific Crawlers
The rise of artificial intelligence has led to new crawlers that collect web content to train language models or deliver AI-based services. These bots are newer and sometimes less transparent than traditional search engine crawlers.
- GPTBot (OpenAI): Used to crawl and index public web content to improve AI models like ChatGPT. It became widely known in 2023 and can be blocked using robots.txt.
- ClaudeBot (Anthropic): Claude is another AI chatbot, and its bot crawls pages for training and reference purposes.
- CCBot (Common Crawl): This is a non-commercial crawler that provides data for AI research, search engine projects, and large datasets.
- Bytespider (ByteDance): Created by the parent company of TikTok, this bot is often used for content analysis and research.
Other Notable Bots (SEO Tools, Scrapers, Aggregators)
These bots may help you with SEO insights or analytics, but some can be resource-heavy or invasive if left unmanaged.
- AhrefsBot and SemrushBot: These are used by SEO professionals to analyze backlinks, keyword rankings, and competitor data. They are useful but can create a high crawl load.
- MJ12bot (Majestic): A well-known crawler used for link indexing and backlink analysis.
- PetalBot (Huawei): Gaining attention in global markets, this crawler supports Huawei’s search engine.
- DotBot and MojeekBot: These are emerging bots used for smaller or independent search engines.
- Unknown Scrapers and Bad Bots: Many bots do not identify themselves clearly. They may pose as legitimate crawlers but are really scraping your content, probing for vulnerabilities, or draining resources.
To manage your website effectively, you need to keep your crawler list updated. Know which bots are beneficial, which ones are neutral, and which ones you should block or limit. Logging and monitoring traffic can help you identify new user agents and adjust your rules accordingly.
How Crawlers Impact SEO, Analytics And Site Performance
Now that you know the types of bots on your crawler list, let us talk about how they affect your website. Not all bots behave the same. Some help your site grow by improving visibility in search engines. Others can drag your site down by distorting data or consuming resources.
Understanding the impact of crawlers is critical if you want to make smart decisions about which bots to allow, restrict, or block completely.
SEO Benefits from Good Crawlers
Good bots help search engines understand and rank your website. Their presence on your crawler list is usually a good sign. These bots index your pages, discover new content, and monitor updates so your site stays relevant in search results. Here are a few SEO benefits you get from good crawlers:
- Content Indexing: Bots like Googlebot and Bingbot read your content and add it to their search databases. This allows your site to appear in relevant queries.
- Freshness and Updates: Regular crawling helps search engines know when you update a post, publish a new page, or remove outdated content.
- Site Structure Analysis: Crawlers follow internal links and evaluate your website’s hierarchy. This affects how search engines determine the importance of each page.
- Sitemap and Robots.txt Compliance: When you use XML sitemaps and proper robots.txt directives, good bots follow them and prioritize crawling the most important pages.
- Ranking Signals Collection: Search engines gather data on page speed, mobile responsiveness, content quality, and user engagement. Crawlers often trigger this analysis.
Without these crawlers, your site may be invisible to search engines, which means no traffic, no rankings, and no conversions.
Risks from Bad Bots
Bad bots behave very differently. Instead of helping your site, they often waste your bandwidth, distort your data, or even pose security threats. Let us explore how:
- Analytics Distortion: Bots can inflate pageviews, bounce rates, and session counts in your analytics tools. This makes it hard to understand how real users interact with your site.
- Server Load and Performance Issues: Malicious or aggressive bots can overwhelm your server with too many requests. This slows down your site for real visitors and can even lead to crashes.
- Content Scraping: Scrapers steal your content and republish it without permission. This can hurt your rankings if Google finds the stolen version first.
- Price and Data Theft: eCommerce sites are often targeted by bots that scrape prices, product descriptions, or stock data. Competitors may use this data for unfair advantage.
- Ad Fraud and Click Abuse: Some bots are designed to click on ads to inflate traffic and costs, or to simulate user behavior and deceive ad tracking systems.
- Security Risks: Some bots look for vulnerabilities like open ports, outdated plugins, or misconfigured servers. These can lead to malware infections or data breaches.
Bot Management Strategies And Tools
Managing bots is not just about blocking bad ones. It is about building a smart system that protects your website while allowing helpful bots to do their job. A clear bot management strategy is essential for your server health, SEO performance, and security. It starts with understanding how to identify bots, then using the right tools and rules to manage them effectively.
Let us look at the most important methods and tools you can use to control the traffic from your crawler list.
How to Use robots.txt And Sitemaps Effectively
The robots.txt file is your first line of control over how bots behave on your site. It is a simple text file placed in the root directory of your domain (like yourdomain.com/robots.txt). This file gives instructions to bots on which pages they can or cannot visit. Here is how it works:
- Allow and Disallow: You can allow or block entire sections of your site. For example, you might disallow /private/ or /cart/ if those pages do not need to be crawled.
- User-agent Rules: You can write different rules for different bots. For example, one rule for Googlebot and another for SemrushBot.
- Crawl-delay: Some crawlers support this directive. It tells them to wait a few seconds between requests. This reduces server load.
However, keep in mind that robots.txt is only a request. Good bots follow it. Bad bots often ignore it. That is why robots.txt should not be your only protection.
Sitemaps, on the other hand, help good bots crawl your site more efficiently. A sitemap is an XML file that lists all the important pages on your site. It helps crawlers understand your structure and prioritize content.
When you submit a sitemap to Google Search Console or Bing Webmaster Tools, it tells search engines where your key content is located and how often it changes. This can speed up indexing and improve your visibility.
Identification Methods: User-Agent + IP Verification
Every bot that visits your site sends a user-agent string. This is like an ID tag that tells you which software is making the request. For example: Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)
By analyzing user-agents, you can detect and categorize crawlers. You can allow verified ones and block suspicious ones. But it is not always simple. Some malicious bots spoof legitimate user-agents to avoid detection.
To improve accuracy, you can verify bots by checking their IP addresses. For instance:
- Google offers a reverse DNS check so you can confirm that a bot claiming to be Googlebot is really from Google’s network.
- Cloudflare and other services allow you to set rules that allow only verified IP ranges from trusted bots.
This extra verification is useful when you want to allow crawlers like GPTBot or ClaudeBot while keeping out impersonators.
Bot Detection And Behavior Monitoring
Besides static rules, you can also monitor how bots behave in real-time. This helps you detect unusual activity, like:
- High request rates from one IP
- Crawling restricted pages
- Ignoring crawl-delay or robots.txt
- Accessing scripts or backend paths
Behavioral analysis can flag bots that disguise themselves as regular users. Many modern systems use machine learning to detect patterns in bot traffic and flag anomalies. These systems analyze timing, request headers, page paths, and session behavior. Some platforms offer dashboards where you can:
- View real-time bot activity
- See which bots consume the most bandwidth
- Detect unknown crawlers
- Set automated rules for response
Manage Bot with xCloud’s AI Bot Blocker
Several tools and services help manage bots on your site. These platforms combine detection, reporting, and mitigation into one system.
To manage bots effectively, you need the right tools. Several platforms now offer complete solutions that combine bot detection, behavior tracking, and real-time protection. Popular services include Cloudflare Bot Management, DataDome, Akamai Bot Manager, HUMAN Security, Imperva, and Radware. These tools help you monitor crawler activity, control access, and defend against malicious bots that may steal content or overload your server.
To block bots effectively, you can use xCloud’s AI Bot Blocker. This tool uses advanced AI to detect bots based on behavior, not just user-agent strings. It helps you stop impersonators, scrapers, and high-frequency crawlers before they harm your site. You can allow verified bots, block unknown ones, and set crawl limits with ease.
Watch the detailed video here to see how xCloud’s AI Bot Blocker works and how it can protect your content and performance.
Best Practices for Managing Your Crawler List
Once you understand which bots are accessing your site, the next step is to manage them wisely. Having a complete and up-to-date crawler list allows you to create a balanced strategy. You want to let useful bots in, slow down the noisy ones, and block the ones that bring harm. Here are key best practices for managing your crawler list effectively.
Allow Good Bots And Block or Limit Bad Bots
The most important rule is simple: encourage helpful crawlers, discourage harmful ones.
Good bots follow crawling rules and bring real benefits. These include Googlebot, Bingbot, Applebot, and trusted SEO tools like AhrefsBot. You should make sure they are not unintentionally blocked.
Bad bots often ignore robots.txt, disguise their user agents, and crawl aggressively. These include scrapers, brute force tools, and some AI bots that do not respect your rules. These bots can:
- Copy your content
- Consume your bandwidth
- Distort your analytics
- Scan for vulnerabilities
To stop bad bots, use layered controls like:
- Blocking user-agents by name
- Rate-limiting access per IP
- Denying suspicious IP ranges
- Using captchas or bot challenges
This way, you reduce server load and protect your data without affecting useful crawlers.
Customize Per-Bot Crawl-Delay And Access
Some bots behave well but crawl too frequently. If you allow them unrestricted access, they may overload your server or slow down your site. To manage this, you can:
- Set a crawl-delay in robots.txt for specific bots
- Limit access to high-impact pages
- Exclude unnecessary directories from crawling
- Allow bots only during off-peak hours (if your server supports scheduling)
For example, you might allow AhrefsBot but tell it to crawl slowly so it does not interfere with real user traffic. This way, you keep the benefits of SEO tools and data indexing without hurting site performance.
Regular Review and Adjustment of Policies
Your bot management policy is not something you write once and forget. The crawler ecosystem changes constantly, especially with the rise of AI bots, new search platforms, and evolving scraping techniques.
Every few weeks or months, you should:
- Review server logs to identify new user-agents
- Add or remove bots from your crawler list
- Adjust crawl delays or access based on current server load
- Re-verify bot IPs to ensure they are genuine
- Monitor traffic for abnormal spikes or bot-like behavior
Keeping your crawler list updated is like tuning a machine. It improves performance, prevents breakdowns, and supports long-term stability.
Logging, Analytics, And Internal Link Auditing
To manage bots effectively, you need data. Use logging tools or analytics software to track crawler behavior. These tools can tell you:
- Which bots access your site most often
- Which pages they visit
- How much bandwidth they use
- Whether they follow your rules
You can also use this data to optimize your internal linking. Crawlers depend on links to find new pages. If important pages are buried too deep or have no internal links pointing to them, they may be ignored. Here’s how to support crawler access:
- Make sure your important content is reachable from your homepage
- Use clean, crawlable internal links (avoid JavaScript-based navigation)
- Check your sitemap regularly and update it when you add or remove content
- Identify orphaned pages and link to them from relevant parts of your site
Internal link audits help both humans and bots discover your content. A strong internal structure improves crawl efficiency and SEO performance.
With these best practices, your crawler list becomes a powerful tool. You will know who is visiting your site, why they are there, and how to control the experience. You will also protect your content, speed up your pages, and keep your analytics clean.
Frequently Asked Questions
2. What should I allow in robots.txt vs. block at the server or firewall level?
Use robots.txt to guide good bots. It is ideal for:
- Controlling access to certain directories
- Setting crawl delays
- Directing bots to your sitemap
However, robots.txt is not secure. Bad bots often ignore it. For stronger protection, block malicious bots at:
- Firewall or CDN level (e.g., Cloudflare)
- Web server rules (like Apache’s .htaccess or NGINX rules)
- Bot management platforms (like Cloudflare, xCloud’s AI Bot Blocker)
Combine both methods for layered security. Use robots.txt to guide good bots and stronger tools to block the bad ones.
3. How can I verify if a bot is genuine (e.g., Googlebot, GPTBot)?
Some bots pretend to be trusted crawlers. To confirm a bot’s identity, do a reverse DNS lookup on its IP address. For example:
- If a bot claims to be Googlebot, verify its IP resolves to *.googlebot.com.
- Google provides an official verification guide.
- OpenAI and Anthropic also publish guidelines and IP ranges for GPTBot and ClaudeBot.
Do not trust the user-agent alone. Spoofing it is easy. Always check the source IP if security is a concern.
4. Should I allow AI bots that crawl my content for training purposes?
This depends on your content strategy. Allowing AI bots may:
- Help your content show up in AI-generated answers
- Expose your content to broader audiences
- Lead to backlinks and visibility
However, it also comes with risks:
- Your content may be used without credit
- Bots may crawl aggressively
- You lose control over how your words are reused
To block AI bots like GPTBot or ClaudeBot, add this to your robots.txt:
User-agent: GPTBot
Disallow: /
User-agent: ClaudeBot
Disallow: /
Some site owners also implement CAPTCHAs, JavaScript challenges, or paywalls to limit access. It depends on your goals.
Wrapping Up: So, Why Does Your Crawler List And Bot Management Matter?
Bots make up most of your traffic. Some bots boost your SEO and help users find your content. Others scrape, overload, or deceive. If you want control, speed, security, and clean data, you need to manage your crawler list.
Use smart rules, reliable tools like xCloud’s AI Bot Blocker, and monitor everything. With good bot management, your site will be faster, safer, and more visible to the right audience.
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