In March 2009, Wolfram announced Wolfram Alpha, an answer engine. WolframAlpha later launched in May 2009, and a paid-for version with extra features launched in February 2012 that was met with criticism for its high price that was later dropped from $50.00 to $2.00. The engine is based on natural language processing and a large library of rules-based algorithms. The application programming interface allows other applications to extend and enhance Wolfram Alpha.