Sunnyvale-based Yahoo announced Wednesday morning that it has entered into a definitive agreement to acquire substantially all of the assets of Tensa Kft., which makes the IndexTools web analytics software. Financial terms of the acquisition were not disclosed. According to Yahoo, it will use the acquisition to expand its sets of services for the online marketing area. IndexTools develops web analytics software focused on online marketing. Yahoo said it will use the technology at first to help small and medium businesses marketing on the web with Yahoo.