A mobile user clicks a link in a smartphone app. Another app automatically opens inside the first to the exact page the user was looking for. When that happens, the user doesn’t question how she or he got there. It just works. Behind those responsive intra-app connections are mobile deep links, the hidden underlying mechanisms driving a more intuitive mobile experience.

Mobile deep linking is a technology still in its relative infancy. Deep links have permeated the Worldwide Web for decades, but the movement to equip the mobile world with robust app-to-app connections didn’t truly take off until this year, when Facebook, Google and Twitter each publicly unveiled their own mobile deep-linking efforts. Facebook announced App Links at F8. Google announced App Indexing at I/O. Twitter has App Cards, and acquired mobile ad startup TapCommerce. Apple’s Extensions announced at WWDC are a more controlled foray into app linking. Even Yahoo entered the mix with its acquisition of mobile analytics company Flurry.

Developers, startups and tech giants alike are pouring manpower and resources into building engines, indexes and tools for both individual and cross-platform mobile deep links.

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While the pros and use cases of weaving an interconnected network of deep-linked native apps are many, the most powerful force propelling this innovation is business. App developers and companies of every size are invested in creating another lasting way to foster user engagement and ultimately grow mobile ad revenue. That’s what big tech companies as well as mobile deep linking and retargeting startups like Deeplink.me, TapCommerce, URX, Quixey and others are after. Beyond the current influx of app installs, re-engaging users without having to rely on spammy push notifications is what the deep-linking community believes will deliver the next wave of mobile commerce dollars.

“In simple terms, mobile deep linking is the ability for an app running on a mobile device to link to another app or cause another app to launch,” said Jason Clark, engineering manager for Facebook’s App Links. “Similar to the Web, the apps can actually package information to each other in order to do something specific. For instance, app A calls into app B and says display something specific like a product or a person’s profile. That’s basically it. The big difference on mobile versus Web is that with mobile this is happening from one app running on the device to another without the help of a browser doing the coordination, whereas in Web there’s a browser that coordinates linking from one page to the next.”

The current use cases for mobile deep links range from targeted advertising and engagement to straightforward functionality and app grouping. A consumer app developer might create a deep link path to a taxi app in the form of a “Call Uber” button. A large app such as Spotify uses specific deep links for its countless in-app pages and music archives; Facebook deep-links between its native app and Messenger; LinkedIn has a half-dozen different apps with narrow purposes bundled together via deep links.

Mobile deep linking is rife with possibility and potential, yet the biggest hurdle facing a technology as new as this one is whether the siloed landscape of corporations, startups and competing open-source standards can coalesce. Developer adoption is the next phase in making mobile deep links not only more intuitive, but ubiquitous across platforms. To achieve that, developers need tools to simplify the process and a universal standard of common practices to unify it.

Diving into deep links
The Internet has conditioned a generation of consumers to expect linked content to do what they want without thinking about it, and the coming generation of mobile users will expect the same.

A deep link, in its purest Web sense, is a hyperlink that links directly to a specific piece of indexed or searchable content on a Web page. For a mobile deep link, that means HTML tags on a Web page or code within an application serving as a roadmap of sorts, mapping a path from one native app to the corresponding deep link in another on a mobile operating system like Android or iOS.

“The Web provided a very common mechanism across all platforms, and it still took a while to really achieve its full potential,” Facebook’s Clark said. “If you look at mobile, linking between apps is a no-brainer just because of the successes of the Web. If I’m an app developer, I’d want to look at the trade-off of cost versus potential value.”

Deep linking begins with tags. Google, Twitter and Facebook all have them; pieces of code developers can integrate so their apps will appear in targeted Google search results or in a user’s Facebook or Twitter feed. The tags are self-serving by design. They’re another way to drive user engagement to a specific platform, capitalizing on deep links for mobile commerce and ad dollars. With recent offerings like App Indexing and App Links, Google and Facebook are going after the developer adoption they know is crucial to ensuring their mobile deep links take root.

App Links is the only truly cross-platform mobile deep-linking solution of the big players, and Facebook has made a point of coloring it with an open-source philosophy and ecosystem.
“We’ve had a deep-linking product at Facebook for a number of years now, but much like other deep-linking technologies it was very specific and hard-wired to our single scenario,” Clark said. “We wanted to open this up and make it so a single investment in deep linking for an app can accrue value for multiple uses.”

Clark explained that App Links provides developers a common addressability mechanism, building on top of existing Web technologies such as URLs to implement deep links across the plumbing of different mobile operating systems, including Android, iOS and Windows Phone.

“Philosophically, the whole idea of being cross-platform is just a nerdy way of saying familiar to people,” Clark said. “If you look at the way people work with linking, they don’t stop and ask, does my friend use the same brand of phone as I do? They just send a link to them. They don’t really care one way or the other whether that link is being served in a Web-ish way or an app-ish way. They just send the link and expect their friend to be able to see the content.”

A startup targeting developers
App Links is an example of how the deep-linking arm of a global tech giant is reaching out to mobile developers. But on a smaller scale, mobile deep-linking startup URX is approaching deep links from an entirely developer-focused perspective.

(Related: URX’s App Search API for deep linking)

URX is building a search engine and app index for deep linking, and has released an API and documentation to simplify the deep linking process for developers. URX aims to break down one of the biggest barriers to developer adoption—the time-intensive process of actually coding a mobile deep link.

“We’re starting to build an index of apps, the content inside them and also the actions they let users take. Then our API will allow developers access to that information,” said URX head of marketing Mike Fyall. “If apps use a Twitter tag, Google tag or Facebook App Link tag, we can crawl their site just like Google might do. Developers can then say, what would be contextually relevant to my user if they’re looking at this type of content.”

The developer benefit of a deep-linking tool such as the URX App Search API is twofold. The developer—with deeper access into the app’s data—can provide richer information on users for mobile advertisers, making the app more attractive for ads. It’s also easier for a developer to create the exact app-to-app connection he or she wants. Using the API to browse the app index, developers can customize a user flow and deep-linked pathway, creating the same intuitive effect on user experience with a simple mix-and-match, rather than a laborious coding process.

Tools like the URX API can also help developers avoid the extra work of deep-linking fragmentation, having to add two or three similar sets of tags to their apps for different search and social platforms.

“What we’ve done on top of just accessing the tags is to ask what the page is about, so we can associate the tags with the content on the page,” Fyall said. “It looks silly, because developers say I want to use Facebook and Twitter to advertise and I also want to show up in Google search results, so they put three sets of tags on their Web page. They’re all doing the exact same thing, they’re just formatted differently.”

Standards, fragmentation and profit
The mobile world gains many more worldwide users every day, but advertisers aren’t yet convinced mobile is an effective method to advertise their brand, according to Beth Kindig, a developer and publisher relations manager at in-app advertising startup Vungle. Deep links are the best hope of platform providers and app developers to prove mobile is really the next great advertising market.

“Facebook, Twitter and Google as well, they’re motivated because they see all the dollars in app install ads today,” agreed Fyall. “Three or four years from now it’s not going to be 90% of dollars on app installs, it’ll be a lot more balanced. So if they want to get that next set of dollars on mobile it’ll be though reengagement, and in order to do that you need deep links set up properly.”
Kindig sees a large gap between the growing number of mobile users and the corresponding ad dollars. Deep linking provides the targeted engagement to close it.

“We have seven billion mobile users, but ad spending is below the Internet right now, it’s below TV and below print. The interesting part about mobile is that the time spent is only going to increase, increase, increase,” Kindig said. “What will we do to close that gap? Deep linking will potentially close that gap because you have a pathway for the user to convert on mobile. This essentially helps an advertiser bring a customer closer to their product. That’s why deep linking is really big and being validated by Facebook, Google and Twitter.”

Despite the strong driver of mobile monetization, developer and audience uptake of deep linking is slow. On one side of changing that equation are Facebook, Google and Twitter, and on the other are URX and other startups such as Quixey, which is making apps searchable from a consumer-focused viewpoint.

Quixey is developing a mobile search capability that allows users to express a normal search query, just like on the Web, matched directly to the most relevant piece of a native app. Whereas URX is indexing and searching from the developer side, Quixey puts the control in the consumer’s hands.

“We understand the value of crawling the content inside native apps, and building a system to link users directly to that content. We call this capability Deep Search,” said Phillip Nelson, Quixey director of product management. “Quixey started trying to organize apps themselves, so you could express a query like, “I want to cook some Thai food.” Now we’re working with developers to index and organize the content inside their apps to match not just which apps help users achieve their need of cooking Thai food, but answer the user’s intent with a variety of options.”

To create that new marketplace populated with deep links, developers and comprehensive mobile app search, Quixey has a mobile deep linking standard called AppURL, and it has fairly wide adoption among mobile startups and small companies. The problem is that every other mobile deep linking startup and large company has its own standard, too.

Facebook’s App Links specification is vying with Google’s App Indexing and Twitter’s App Cards, built off its existing Twitter Card structure, to become an industry standard. URX is advancing its own technology, called Omnilinks, as is Deeplink.me. Another open-source specification, mobiledeeplinking.org, has the backing of Twitter’s recently acquired TapCommerce and others including Vungle and Flurry.

The mobile deep-linking community openly acknowledges the need for a universal standard to increase developer uptake and industry adoption. Yet in the early stages of getting mobile deep links off the ground, fragmented and siloed efforts have resulted in an array of convoluted specifications.

Deeplink Tags by Platform (1)

Deep link tags by platform. (Source:URX.)

“If someone could’ve gone back and mentioned a standard five years ago, we wouldn’t be having all this trouble,” said URX’s Fyall. “But we didn’t, so they each naturally evolved into their own thing.”
On the OS level, Android and iOS govern how deep links are implemented in apps. The standards exist on the Web level, the link structure for recognizing a deep link on different platforms. URX did a study this past July, measuring how many of the current top 200 mobile apps by download use deep links, the specific website mapping tags to an app’s URI scheme. Their research found that only 22% of apps had deep links, and only 8% of apps contained deep links for both Android and iOS.

URX is trying, with its own cross-platform API and standard, to clean up the mess of tags and link structures developers are faced with to make deep links accessible for all. Even that, though, sows more fragmentation on a structural level. Vungle’s Kindig said that despite their good intentions, the individual specifications of URX, Deeplink.me and others are not operating on a standardized URL backbone, the link structure a mobile OS parses to establish a deep link.

“I think what URX and Deeplink.me are doing is great, but it’ll never solve the problem,” Kindig said. “What needs to happen is more people need to contribute an open-source initiative like mobiledeeplinking.org or another, so that any capable developer can move forward with deep linking on their own. URX has its own URL. Facebook has its own version of a URL, when you look at mobile. So that’s the problem. It’s all fragmented, and it’s very monopolized. The future and the solution is a universal standard.”

On the open-source side, standards like mobiledeeplinking.org simply don’t have the traction or backing of larger companies to get the open-source contributions they need for adoption. Facebook’s view of competing open-source standards is that they’ll eventually converge into a handful of approaches rather than dozens. Yet in the short term, Clark said while App Links doesn’t want to get in the way of other efforts, Facebook is still pushing ahead with its own.

“Whether it’s a formal standard or just a coalition of partner companies, we are non-dogmatic about it. But at the end of the day, getting something common that folks can march in the same direction to is very valuable,” Clark said. “The phase we’re in right now is very exploratory, so we’re trying to get as many impressions and opinions about what matters in mobile linking on the table so we can sort through them and put the most broadly applicable protocol in place.”

Clark said the App Links specification would continue to iterate over the next year or two to “discover all the nooks and crannies of this space so that we don’t miss something. It’s really a goal of ours to make sure we understand all the needs of the ecosystem,” he said.

Whether it’s URX, Facebook or Google, each company’s proprietary index of native deep linkable content isn’t interoperable. It’s a row of walled gardens. Quixey’s Nelson draws a parallel between Google’s deep linking on the Web almost two decades ago, and now on mobile with application content locked up in silos across its different verticals. Whereas now mobile deep links are evolving into a fragmented landscape, it was the original freedom and openness of the Web that allowed Google to thrive.

“In the early stages of the Web, it was easy for two really brilliant guys at Stanford to crawl the entire huge graph or subset of the Web in the late ‘90s and invent a new search product called Google,” Nelson said. “What’s happening right now is you have these large app experiences with huge power, and they’re deciding we’re not going to publish ourselves in the open, native, deep-linkable graph.”

An invisible steppingstone
The mobile deep-linking caravan of startups, corporations and developers may be moving in a host of different directions, but it’s undoubtedly moving. Deep links are the foundation of the Web, and the new mobile web of app-to-app connectivity cannot experience the same period of growth and intuitive experience innovation without the intricate deep-linked application paths dug underneath.

“Users shouldn’t know this is any different from what they were doing on the Web, and yet they should have all the benefits of a lovely experience with their device of choice. It shouldn’t feel like something the user has to opt into,” said Facebook’s Clark. “I think we’ve only really scratched the surface of its potential. There’s already a ton of engagement and activity, but the missing piece is ubiquity. Having something that’s consistent across all platforms will cause an explosion in opportunity.”

If mobile deep-linking companies and developers do their jobs right, deep links will serve as the steppingstones to a more robust, intuitive mobile web of connected apps. The deep links themselves, though, will be largely unseen.

“The inner plumbing of how native or mobile deep linking works should be completely invisible to the user,” said Quixey’s Nelson. “Where that takes us, we can only speculate. On the Web you had this density and structure [of deep links,] but there wasn’t that richness of semantic knowledge to a layperson that a computer as well as a human could understand. The understanding of what that link actually does. That’s something we can bake into these new capabilities from the start.”