After testing its platform for buying and selling mobile ads for six months, Santa Monica startup Gradient X has made its technology publicly available.

The company, housed in a hangar at the Santa Monica Municipal Airport, operates a real-time bidding platform for mobile ad transactions. It also provides back-end software so marketers can track the performance of their ads.

Gradient X was founded by a team of ad tech veterans with experience at L.A. firms such as Rubicon Project and Adconian Media Group.

Brian Baumgart, the firm’s founder and chief executive, watched the explosion in the use of mobile devices to browse the Web and connect to the Internet. But he realized that ad technology for the mobile space had not yet caught up.

“To date, agencies and advertisers have not been able to invest in mobile at the levels they’d like to due to these shortcomings,” Baumgart said in a statement. “The Gradient X mobile platform explicitly tackles these issues by providing unparalleled transparency, audience data and brand safety, all via real-time bidding.”

Gradient X is backed by a number of local investors, including Upfront Ventures (formerly GRP Partners), Rincon Venture Partners, Crosscut Ventures and Siemer Ventures.

The company claims access to more than 400 million unique mobile devices and said ads on its platform had been viewed more than 50 billion times.