Blekko, a search engine that will open to the public on Monday, aims to show search results from only useful, trustworthy sites.

Blekko’s search engine scours three billion Web pages that it considers worthwhile, but it shows only the top results on any given topic. It calls its edited lists of Web sites slashtags. The engine also tries to weed out Web pages created by so-called content farms like Demand Media that determine popular Web search topics and then hire people at low pay to write articles on those topics for sites like eHow.com.

People who search for a topic in one of seven categories that Blekko considers to be polluted with spamlike search results — health, recipes, autos, hotels, song lyrics, personal finance and colleges — automatically see edited results.