Beginner's Guide to ASO

Even if you don't know anything about App Store Optimization, these lessons will get you up to speed quickly

Lesson 3: Prioritizing Relevance, Traffic, and Difficulty

The core of app store keyword optimization includes the three main characteristics of keywords: Relevance, Traffic, and DifficultyYou will examine every keyword based on these criteria for both the Apple App Store and Google Play. This lesson will go over these criteria in detail so you can understand how to use each of these criteria appropriately.

While Traffic is an essential metric in selecting keywords, many publishers make the mistake of choosing keywords solely based on traffic volume. Although it is ideal to rank for keywords that get a ton of searches, relevance, and difficulty are also important when it comes to increasing organic downloads on the app stores.



Relevance is the most important criterion when it comes to choosing keywords. Your keywords need to be terms that people would search for to find your app on the app stores. The relevancy of the keyword is how your keyword relates to your app's usage and goals.

One way to think about relevancy is to put yourself in the shoes of your ideal user. Think about technical terms, abbreviations, and phrases they might use while searching for your app in the app store or when describing your app to a friend. Since you are so deeply involved with your app, it can sometimes be hard to get an objective perspective as to what people would search for. Friends, family, and even random strangers can be great sources of relevant keyword ideas.

Our next lesson will give you a lot more tips on how to discover keywords. But for now, keep in mind that relevance should be your primary selection criterion.



Traffic is the second criterion when selecting keywords. Different ASO platforms will measure traffic in different ways.

At Sensor Tower, we created a Traffic Score, which is our estimate of how many searches a keyword gets in the app store. It is on a logarithmic scale from 0 to 10, with ten being the most searched for keywords. A higher score indicates your app can reach more people if you rank well for that keyword.



For example, let's say that you want to replace one of your underperforming keywords in your iTunes keyword list, such as a keyword ranking higher than #18 in the app store. You are trying to decide between the following two keywords, and both have similar relevancy.


Keyword #1:

  • Traffic Score: 5.3
  • Difficulty Score: 4.4 

Keyword #2:

  • Traffic Score: 6.2
  • Difficulty Score: 4.4

In this case, you would choose Keyword #2 because it gets more traffic than Keyword #1.



Lastly, you want to consider Difficulty when deciding on keywords, which is how hard it is to rank for each keyword on your list. Similar to traffic, different ASO platforms measure this in different ways.

At Sensor Tower, we quantify difficulty with our Difficulty Score. It estimates how hard it will be to rank in the top apps for a selected keyword. We use a logarithmic scale from 0 to 10, with ten being the most difficult. A higher score indicates it is tougher for your app to be in the top-ranked apps for this keyword.

When researching iOS apps on Sensor Tower's platform, you will see Difficulty Scores for both iPhone and iPad. Since there are different scores for each device, you need to take this into account when choosing your keywords.

If you have an app that is only for the iPhone, then you will solely focus on that Difficulty Score. If you have a universal app, then you have to take both scores into account.



We show only one Difficulty Score for Google Play Android apps.




Ideally, your keyword will have a high traffic score and a low difficulty score. It is important to note that keywords with higher Difficulty Scores generally have more traffic. Since frequently searched keywords are the most advantageous, they will have the highest traffic and difficulty scores.

Balancing the traffic score with the difficulty score is also a critical component of keyword optimization. It doesn't matter if the traffic score for a keyword is 9.2 and there are a million searches a day for a keyword, if the difficulty score is 9.0 and you rank #512 for that keyword, nobody will see your app.

A good Difficulty Score depends on how established your app is. If you have an app that is established and already has a lot of downloads, you will be able to rank well for keywords with a higher Difficulty Score. If you are just starting, then you will have to target lower Difficulty Scores. The next section will dive deeper into finding out a target Difficulty Score.

Established Apps

If your app has been available on iTunes or Google Play for more than a month and you have already done some optimization, figuring out your target Difficulty Score is simple. Just take the average of the Difficulty Scores that you currently rank in the top 10 for, and that number is your Target Score.

For example, let's say that this is a sample of your top keywords and how your app ranks for those keywords. You have a universal iOS app, so you need to take into account the keywords for both iPhone and iPad.



In this case, you would average the Difficulty Scores of the first two keywords because your app ranks in the top 10 for them. The keyword "enigma" would not factor into this calculation. Although the rankings for this keyword are still quite good, they are not in the top 10 and should not be used in your equation.


This would give you a target Difficulty Score of:


2.6 + 3.7 + 4.9 + 5.1 = 16.3


16.3 / 4 = 4.0

So you should target keywords that have a difficulty score of 4.0 or less.


Our Difficulty Score is an excellent approximation of how hard it is to rank in the top apps for a keyword. However, this is an approximation, and conditions on the app stores change all the time. You still need to test and track your keywords continually to improve your rankings.

For example, let's say that you want to add ten new keywords to your app. They all have very similar Difficulty Scores. After you add your keywords to your list, your app might rank in the top 10 for eight of those keywords.

Since the ranking algorithms for iTunes and Google Play are closely guarded secrets, there could be a variety of unknown reasons why you did not rank in the top 10 for those last two keywords. The best thing to do is to just replace them with keywords that have a similar Difficulty Score and track the results.

If you're curious about what the Difficulty Scores of your current keywords are, you can find out using our free trial.

New Apps

If you have a new or unpublished app or an app that does not have any keywords in the top 10, you cannot determine a target Difficulty Score. In these cases, we recommend targeting keywords with a Difficulty Score of 3.0 or less.

Once you publish your app or submit an update, you will have more data and can make adjustments to your keywords using the available data. It can be hard to find one-word keywords with a score of 3.0 or less, so remember to also look for multiple-word keywords. Getting more specific increases the chances of ranking well for your target keywords.

Note: Keywords can contain one or multiple individual words. The word "castle" is a keyword, but the phrase "castle defense" is also referred to as a keyword in ASO.


When you sit down to research your keywords, remember these three criteria: Relevance, Traffic, and Difficulty. Applying these criteria will help you maximize your ASO potential and thoroughly optimize your keyword string.


In our next lesson, we will show you exactly how to track your keyword rankings, research your competition, and brainstorm for keyword ideas.

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