App store optimization (ASO) is the process of improving the visibility of a mobile app (such as an iPhone, iPad, Android, BlackBerry or Windows Phone app) in an app store (such as iTunes for iOS, Google Play for Android, Windows Store for Windows Phone or BlackBerry World for BlackBerry). Just like search engine optimization (SEO) is for websites, app store optimization is for mobile apps. Specifically, app store optimization includes the process of ranking highly in an app store's search results and top charts rankings. Additionally, app store optimization also encompasses activities focused on increasing the conversion of app store impressions into downloads (e.g. A/B testing of screenshots), collectively referred to as Conversion Rate Optimization (CRO). ASO marketers and mobile marketing companies agree that ranking higher in search results and top charts rankings will drive more downloads for an app.. Earning an app store feature and web search app indexing are two additional activities which may be categorized within the remit of app store optimization.
Apple's iTunes App Store was launched July 10, 2008, along with the release of the iPhone 3G. It currently supports iOS, including iPhone and iPad. There is also a non-mobile app store for Macs. Google's app store, Google Play, was launched September 23, 2008. It was originally named Android Market and supports the Android operating system. Since the launch of iTunes App Store and Google Play, there has been an explosion in both the number of app stores and the size of the stores (amount of apps and number of downloads). In 2010, Apple's App Store grew to process USD$1.78 billion worth of apps. iTunes App Store had 435,000 apps as of July 11, 2011, while Google Play had 438,000 as of May 1, 2012.. By 2016, Apple's App Store had surpassed 2 million total apps and Apple had paid out close to $50 billion in revenue to developers.. Industry predictions estimate that by 2020, the App Store will hold over 5 million apps.
As the number of apps in app stores has grown, the possibility of any one app being found has dropped. This has led app marketers[who?] to realize how important it is to be noticed within an app store. As marketers started working on ranking highly in top charts and search results, a new discipline was formed and some app marketers have reported success.
The first use of the term "app store optimization" to describe this new discipline appears to have been in a presentation by Johannes Borchardt on November 4, 2009. It began to take hold as a standardized term not long after, with outlets such as Search Engine Watch and TechCrunch using the term by February, 2012.
App store optimization works by optimizing a target app's keyword metadata in order to earn higher ranks for relevant keywords in the search engine results page, as well as increasing the rate at which users decide to download that target app. ASO marketers try to achieve goals, such as:
Many ASO marketers categorize their work into two distinct processes: keyword optimization and conversion rate optimization.
One of the main jobs of an ASO marketer is to optimize the keywords in an app's metadata, so that the app store keyword ranking algorithms rank that app higher in the search engine results page for relevant keywords. This is accomplished by ensuring that relevant and important keywords are found in an app's metadata, as well as adjusting the mix of keywords across an app's metadata elements in order to increase the ranking strength of target keywords. 
In order to increase the downloads of an app, an app's assets (e.g. the icon, preview video, screenshots, etc.) must also be optimized. It is recommended to measure the effect of these optimizations by creating different variations of each asset, showing each variation to users, and then comparing the conversion rate of each variant, in a process referred to as A/B testing. Google Play facilitates this process by providing ASO marketers with an A/B testing platform built into the Google Play Console. For other platforms such as the Apple App Store, ASO marketers can run A/B tests via 3rd party A/B testing tools, running a pre-post test (i.e. pushing new assets live to the store and measuring the impact pre-and-post change), a country-by-country experiment (i.e. testing different asset variations across similar countries, such as UK/AU/CA/US/NZ), or testing different variations via ad platforms such as Facebook Ads.
Around 84% apps in the app store did not have keywords in their titles. the other hand, only 16% apps used keywords in the app titles. While the app store search algorithm is always changing, some have suggested that keywords in the app title may have more impact on rankings than those entered in the Keywords field.
The app icon is the first visual element that people see when they view an app store listing. An icon should immediately convey what an app is about, in the simplest manner possible. Complex icon designs can be difficult to distinguish on smaller devices and should be avoided.
Screenshots are also one of the first visual elements that people see when viewing an app listing. Each screenshot should convey a specific benefit of the app and supplemental text should be used, whenever possible, to clarify what each screenshot is about. All available screenshot slots should be used to maximize visibility. The first 2 screenshots are the most important as they are the ones seen when scrolling through search results.
Translating an app into different languages can greatly increase downloads and expose an app to a larger potential audience. In one study, localization increased the downloads of an iPhone app by 767%. Another study showed that complete localization was able to increase app downloads by 300%.
The app description has very different roles in ASO, when comparing the Apple App Store and the Google Play Store. Keywords in the description do not factor into the keywords that Apple associates with the app. However, keywords in the app description of Play Store apps are a primary source of keywords that Google uses to determine what an app is about.
Most app publishers make the mistake of selecting keywords that get a lot of searches every month. What they do not realize is that these keywords are also extremely competitive and most apps will not be able to rank for them. Keywords should first be selected by download relevance, or would people actually download an app, if they searched for that keyword? The next criteria is competition. Does the Chance Score give the app a good chance of ranking in the top 10 for a keyword? Finally, only then should search traffic should be considered. There should be some search traffic for a keyword, but it doesn't have to be a lot. Ranking well for download relevant keywords is much more important. Finding good keywords usually involves targeting long-tail keywords, like in Search Engine Optimization (SEO).
Many app marketers attempt to perform ASO in a way that most app stores would approve of and accept. This is called "white hat" ASO and publicly covered by presentations, conferences. Developers also use different platforms available to get their peers to rate their apps for them which provides great feedback. Some app marketers, however, engage in what many call "black hat" ASO and are practices which the app stores do not condone.
Black hat ASO includes falsifying downloads or ratings and reviews, perhaps by using bots or other techniques to make app stores (and their users) believe an app is more important and influential than it actually is.
Apple has been proactively fighting against black hat ASO. In February, 2012, Apple released a statement as reported by The New York Times "warning app makers that using third-party services to gain top placement in App Store charts could get them banned from the store."
Google followed Apple in 2015 and started manually reviewing apps, to enforce app quality and reduce black hat practices.
At WWDC 2017, Apple announced major changes to its App Store experience arriving with iOS 11. The major implications of iOS 11 for ASO are as follows:
Additionally, Apple now requires developers to use its iOS 10.3 in-app rating prompt, disallowing custom ratings prompts.
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