SpyFu is a competitor research tool. Enter a domain and it reveals the keywords that site ranks for in organic search, the keywords it buys on Google Ads, and how those change over time. The ad history is a distinctive feature, since you can see which ad copy a competitor has tested and kept running.
That data helps marketers decide where to compete. Keyword research shows search volume and difficulty, backlink tools find link opportunities, and rank tracking monitors progress. Agencies use the reports to pitch clients, and PPC managers use the ad history to find ideas and gaps in their own campaigns.
SpyFu has a limited free view and paid plans with pricing that does not scale by number of users, which is popular with small teams. Its data covers mainly the US and other major markets, and estimates are approximations. Alternatives include Semrush, Ahrefs, SE Ranking, Moz, and SimilarWeb. SpyFu suits small agencies and marketers focused on search and paid ads.