How do sites block web crawlers?

The most common way to block data center agents is usually used by crawlers. This applies to most homemade or "free to use" crawlers. In this case, you can avoid using residential proxies because they look like real users and are therefore harder to detect.


1. Mask its IP address. You must collect all of the CRAWler's IP and protect the site by adding them to your blacklist of web servers, firewalls, or any other software or service that may be in use.

With this block, the crawler can't even start connecting to your site, which means you spend the least amount of resources fighting the crawler. You can of course do the same at the application level - by analyzing the IP address of the requester and providing an error, empty reply, or disconnection. But that means you're spending too many resources (including the time you spent writing the logic) instead of just using the facilities of your web server.


2. You can prevent crawlers at a higher level by analyzing the "user-Agent" HTTP header and providing some HTTP errors.

For example, 503, not the content. You can also simply disconnect rather than spend resources on a reply. This means that crawlers do not hide their identity and do not use user agents in some Web browsers. This also means that you spend a considerable amount of system resources on accepting connections, analyzing requests, and providing replies.


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