Can I crawl any website?

When creating a web crawler, one common question is "Can I crawl any website?" The short answer is you technically can crawl any public website, but there are ethical and legal considerations around respecting sites' permissions. This article covers what is allowed and best practices around crawling.

Robots Exclusion Protocol

Websites communicate crawling permissions through a robots.txt file located in the root directory. This Robots Exclusion Protocol tells crawlers which pages they can and cannot access. Most large sites have a robots.txt file, while smaller sites may not.

Here is an example robots.txt file:

User-agent: *
Disallow: /privatepages/
Allow: /publicpages/

This allows crawlers access to /publicpages/ but disallows /privatepages/.

When Can I Crawl a Website?

If a website does not have a robots.txt file or does not explicitly disallow crawling, you technically can crawl it but should do so ethically and legally. However, just because you can does not always mean you should.

Best practice is to respect website owners' permissions and preferences, crawl politely using reasonable resources, and make sure your crawler identifies itself properly in server requests. Overtaxing servers or repeatedly accessing pages against owners' wishes can get your crawler blocked.

What If I Still Want to Crawl a Website?

If you still wish to crawl a website that disallows it, you should first contact the owner directly explaining your intended usage and seeing if they grant permission. Most website owners will work with you if you request access professionally and have a legitimate need.

However, repeatedly crawling private pages after being forbidden could open you up to potential legal issues around violating terms of service or even hacking/intrusion laws in some cases. Be sure you have explicit legal permission first.

The main takeaway is while you technically can crawl many websites, you should first check for permissions, crawl ethically, identify your crawler properly, and respect owners' wishes. Doing so avoids legal risks and keeps your crawling sustainable long-term.