Ask HN: legally can i build search niche web search engine?

i want to build search engine that searching dally niche sites , like blogs first page's then present statistics based on the crawling. legally can i do this ?

There is no legal restriction for crawling any web site. But you should respect robot.txt document for every single web site. Such as: https://www.facebook.com/robots.txt http://web.archive.org/robots.txt