Most indie iOS developers treat the keyword field like a bonus field. They paste in whatever terms came to mind, hit 100 characters, and move on. Some leave it half-empty. Some copy their subtitle into it word for word.

This is the biggest unused lever in iOS app distribution.

The keyword field is not supplementary to your title and subtitle. For most small apps, it is the part of your metadata that gets tested most, changed most, and produces the clearest signal about whether your keyword choices are working. If you are not treating it that way, you are running your ASO strategy with one hand behind your back.

What the keyword field actually does

Apple gives every app a hidden 100-character field per locale in App Store Connect. Users never see it. App Store search reads it.

Every token in that field gets indexed. If you write cardio,strength,hiit,yoga, Apple will consider your app for any search containing those words. If a user searches “hiit workout” and your subtitle says something about interval training but your keyword field has hiit, you have two independent signals telling Apple this app is relevant.

The field is formatted as comma-separated keywords with no spaces around commas. Each locale gets its own 100-character budget. Five active locales means 500 characters of hidden keyword space, completely separate from your titles and subtitles.

Read the full formatting and rules guide for the keyword field.

Why developers underuse it

There are three patterns that drain the keyword field of value.

Duplicating the title and subtitle. If your title is “FitTracker: Workout Log” and your subtitle is “Gym and Cardio Planner,” writing fittracker,workout,gym,cardio,planner in the keyword field is 44 wasted characters. Apple already indexes every word in your title and subtitle. The keyword field is for words that are not anywhere else in your metadata.

Leaving it half-empty. A 60-character keyword field on an app with a 30-character title and 30-character subtitle means you are using 120 of a possible 160 characters per locale. That is 25 percent of your keyword budget unrealized, before accounting for additional locales.

Not thinking across locales. Apple indexes your app’s keywords globally. A German user searching “gym” will find your app if gym is in your English keyword field, even if your German metadata does not contain it. Most teams translate their keyword field word-for-word, which duplicates coverage they already have rather than extending the keyword pool.

The numbers behind the waste

Looking at apps tracked in Marteso, a consistent pattern shows up. Apps that rank in the top 50 for their core terms tend to use 90 or more characters of their keyword field. Apps that struggle to break the top 100 for any term often have keyword fields under 60 characters or filled with words that repeat their title.

This is not a coincidence. The apps with thin keyword fields are not giving Apple enough signal diversity to place them for anything outside their one or two obvious terms.

A fitness app targeting only “workout tracker” is competing against every other fitness app targeting the same obvious term. An app that also covers calisthenics,hiit,strength,plan,routine,abs,trainer is giving Apple ten additional signals about what users it might serve. Even one of those terms ranking in the top 30 adds impressions that “workout tracker” alone cannot.

The keyword field as a test environment

Here is the reframe that changes how you use it.

The keyword field is the safest place in your metadata to experiment. Unlike the title and subtitle, which affect how users perceive your app on the search results page, the keyword field is invisible. Changing it does not change how your app looks. It only changes which searches Apple considers you for.

This makes it the right place to test volume assumptions. You add a keyword, wait 10 to 14 days, check whether rankings appear, and then decide whether to promote that term into your subtitle or title where it would be visible and more heavily weighted.

The workflow looks like this:

  1. Find a keyword with moderate popularity (50 to 80) and low difficulty relative to its popularity.
  2. Add it to the keyword field in your next release.
  3. Check your keyword rankings after two full App Store review cycles (10 to 14 days).
  4. If the term appears in the top 50, it has ranking potential. If it ranks top 20, it is worth testing in the subtitle.
  5. If no ranking appears after 14 days, replace it with a different candidate.

The keyword field is a rotating hypothesis board. Most developers treat it as a static string they set once and forget. Treating it as an active testing layer changes the output.

Common mistakes that cancel out valid keywords

Spaces around commas. Writing keyword1, keyword2 instead of keyword1,keyword2 costs you one character per keyword from a 100-character budget. At ten keywords, that is 10 characters gone.

The word “app.” Nobody types “fitness app” expecting to find an iOS app. They type “fitness” and they are already inside the App Store. The word app buys you nothing and costs you four characters plus a comma.

Singular and plural of the same word. Apple stems most plurals. workout generally covers workouts. Listing both spends two slots on one effective keyword.

Your developer or brand name. Apple indexes your developer name separately. It is not necessary in the keyword field.

Remove any of those patterns from your current field and you typically free up 20 to 30 characters for net-new terms without changing a single content choice.

A field that is worth two hours a month

The 100-character keyword field takes about two hours to optimize properly: audit the current state, remove wasted characters, research replacement candidates, and update. That two hours compounds across every locale you have active.

It is not glamorous. It does not change anything a user ever sees. But it is the lever most indie developers have not pulled, and the one where you are not competing against an established app’s three-year head start. You are competing against developers who have not read this far.