New ask Hacker News story: Anyone Experienced with Crawling Websites?

Anyone Experienced with Crawling Websites?
2 by Flash7755 | 0 comments on Hacker News.
Hello fellow hackers, I am trying to create a tool for myself that can crawl a few websites that I usually go on to compare the price of the same item. They have no APIs. A couple questions: 1. is this LEGAL? 2. if I am crawling, what is the best way to approach this? does each website's crawling mechanism have to be manually written since they are unique or is there some strategy for scale if i need to expand the number of sites I crawl through in the future? Thank you! -F75