What are the rules for web scraping?

Web scraping, or extracting data from websites, can be a useful technique for gathering public information at scale. However, it also carries ethical and legal responsibilities. Here are some guidelines for scraping responsibly:

Respect Robots.txt

Websites use robots.txt files to give instructions about scraping. Before scraping a site, first check http://example.com/robots.txt to see if scraping is allowed or if there are rate limits. Respect what the file says.

Don't Overload Servers

Scraping too aggressively can overload servers. Use throttles and delays between requests so as not to degrade site performance. As a rule of thumb, limit requests to 1 or 2 per second.

Check Terms of Service

Most sites prohibit scraping in their Terms of Service. Review TOS before scraping, and comply with specified limits. Note that Terms may change over time.

Use Structured Data Where Possible

Sites often provide structured data feeds like JSON or XML that are intended for programmatic use. When available, leverage these instead of scraping HTML.

Correctly Attribute Copied Content

If reproducing scraped content verbatim, be sure to attribute it and link back to the source page. Follow copyright principles.

Overall, remember that servers and data belong to others. Scrape ethically by adding delays, respecting opt-outs, minimizing resource use, and citing sources. With conscientiousness and care for site owners, scraping can gather useful data without harm.