It used to take Goldman Sachs Group Inc. bankers days to analyze a company's vulnerability to activist investors. Now, the firm is launching an app that lets clients do it themselves in seconds.

Goldman Sachs has spent two years quietly developing “Jupiter,” a program that sifts historical data on a company's shareholders, then combines that with other information to rate its vulnerability to activists. The firm will offer the app in coming weeks to clients that could become targets of corporate raiders.

The software gauges the risk of an activist attack in several ways. It sifts, for example, funds that own a company's stock, showing how it ranks alongside other holdings. The idea is that a fund manager is more likely to reject an activist's demands if the company already looks good in the portfolio—say, growing revenue faster or paying a higher dividend than other bets. Executives can use that information to ensure they don't fall behind, or they can try to court more investors.