Knowing that a Web site is in trouble is one thing--most network-and systems-management tools will do triggering alerts when a server is crashing or there's a network glitch. Pinpointing the cause is another matter.

But help may be on the way. Mercury Interactive Corp. has added a module to Topaz, its Web-performance monitoring software, designed to let administrators zero in on the most likely causes for problems.

The Auto RCA (root-cause analysis) module is a statistical-analysis engine with built-in rules used to measure system and Web performance. Performance data is compared with the rules; the results can help an administrator pinpoint where trouble originated.

Determining a trouble spot saves IT managers a lot of time, says Jasmine Noel, an analyst at Hurwitz Group. "When customers first see the app tanking, that's when they need RCA," she says. "Without RCA, it's hard to find the piece among the app code, database, server, network, firewall, and all the other features. Topaz with RCA could easily turn a half-hour job into five minutes." Mercury Interactive isn't the first to offer root-cause analysis in its Web-performance tool, Noel says, but most tools require administrators to write the rules themselves.

The Auto RCA module creates a baseline and collects performance data from all aspects of a company's Internet infrastructure. The statistical engine applies those baselines to any system abnormalities Topaz picks up. The comparison pinpoints the most likely source of a problem and filters out the vast amounts of irrelevant data. Auto RCA is available now for $15,000.

PHH Arval, the vehicle-leasing and fleet-management subsidiary of holding company Cendant Corp., installed Mercury Interactive's Auto RCA last week. "Ultimately, we expect it will help make sure the site isn't down, our clients are more satisfied, and increase our revenue," says Tim Talbot, senior VP of IT at the Hunt Valley, Md., company. Fine-tuning the Web site's performance is key, Talbot says, because 30% to 40% of PHH Arval's $2 billion annual revenue comes from the company's growing Internet business.