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This tool is helping Airbnb, Pinterest, and Etsy get more people to download their apps

What good is a user referral program or a marketing campaign if its effectiveness can’t be measured?

Like any other business, companies built on mobile apps—such as Airbnb, Pinterest, Etsy, Washio, Wanelo, and Snapdeal—want to know where their customers come from. Often it’s on the recommendation of a friend, who shared with you the link to download the app in Apple’s App Store or Google’s Play Store. The problem? That process tells the app-maker very little about how you got to that link. The app stores don’t transfer that information to the vendor—obscuring your arrival from, say, Facebook over Google Search. (Ditto sharing a link to specific information within an app, such as a home listing on Airbnb or a pinned Pinterest item.)

Several companies build tools to circumvent this loss of data: Branch Metrics, Tapstream, and a three-year-old company named Yozio, which on Tuesday said it raised $7 million in new funding.

Yozio builds software development kits, or “SDKs,” that are easy to incorporate into mobile applications and makes it so that when a user taps on a link to view an item in an app, Yozio’s servers will remember the action and, using a variety of information to identify the user’s device, will tell the app to show the user that item as soon as the download completes.

Yozio has more than 600 customers, it says, 20 times the number it had when it launched in January.

Yozio lets developers track individual links across Apple iOS, Google Android, and the Web for efforts such as customer referral programs and email marketing campaigns. On Tuesday, the startup added the ability to track links when existing users click or tap on them—a feature that many customers requested, Yozio co-founder and CEO Lei Sun tells Fortune.

“A lot of the people who were clicking were already users. So it looked like they weren’t getting more installs,” Sun says. Yozio’s corporate customers were missing the fact that their existing users were clicking on links—an equally important user behavior they wanted to be able to track.

Though tracking tools from Yozio and its peers aren’t a cure-all, they are growing in importance for developers. The rise of the app economy and in-app commerce has put a premium on such information; the ability to test how various kinds of marketing work can make a world of difference for a startup’s survival. From a transactional standpoint, reducing friction during a purchase process is the ultimate goal of every merchant that fears losing business from potential shoppers who just give up because they couldn’t find the item after downloading and signing into an expensive new shopping app.

Yozio says a big challenge ahead is working in international markets where there are a number of app stores beyond that of Apple and Google. These stores use different technologies, Sun says, and Yozio needs to make sure it can support them, too.

Foundation Capital led Yozio’s latest funding round alongside Illuminate Ventures, Webb Investment Network, and AME Cloud Ventures, among others. Founded in 2012 by Sun and Li Hong, Yozio previously raised $1.6 million in funding.

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