The 100-Character Keyword Field: Apple's Hidden ASO Lever

The 100-character keyword field in App Store Connect is one of the most consistently misused assets in indie ASO. It is invisible to users, indexed for search, and you get exactly 100 characters to fill it. Most apps waste 30-40 of those characters on words Apple already extracts from the title and subtitle.

This guide shows you how to extract maximum value from every byte.

The Rules Apple Does Not Document Clearly

The keyword field has six behaviors that matter. None of them are written in the App Store Connect docs, but all are observable through Apple Search Ads data:

1. Comma-separated, no spaces. Use commas as the only separator. Spaces inside the field count against your 100 chars and generally hurt rather than help.
2. Apple combines keywords across fields. "weather" in your title + "tracker" in your keyword field = your app indexes for "weather tracker" without spending characters on the combination.
3. Singular and plural are different keywords. "tracker" and "trackers" rank separately. Pick whichever has higher Apple Ads popularity.
4. Stopwords are filtered. Articles like "a", "the", and "for" are stripped. Do not waste characters on them.
5. Category name is implicit. "Health & Fitness" is already in your category - you do not need to repeat it in the keyword field.
6. Translations are per-storefront. The 100-char limit applies separately to each localization. You can use the English field and the Spanish field independently.

The Optimization Process

Step 1: List Every Word Apple Already Indexes for You

Before touching the keyword field, write down every keyword Apple has already extracted:

• Every word in your app title
• Every word in your subtitle
• The category name (in your localization)
• Common variants of each (singular/plural Apple often handles)

Anything on this list should NOT appear in your keyword field. Repeating them is duplicate indexing - it gives you no additional rank lift and burns characters.

Step 2: Pull Popularity Scores for Your Candidate Keywords

Apple's own keyword popularity scores (5-100 scale) are available through Apple Search Ads. Anything below 5 is dead - Apple does not even show search volume for it. Anything above 80 is too competitive for an indie app to rank for.

The sweet spot for indie apps in 2026 is keywords with popularity scores between 15 and 50. High enough that real users search for them. Low enough that you can rank top 3.

Step 3: Fill Out the 100 Characters

Order your candidate keywords by popularity score, then start filling the field. Stop when you hit 100 characters. Track exactly how many characters each keyword uses (commas count).

Example for a migraine tracker that already has "Haven - Migraine Diary" as title and "Track triggers in 30s" as subtitle:

Wasted version	Optimized version
migraine,headache,tracker,diary,trigger,health,wellness,track	headache,trigger,journal,weather,cycle,sleep,relief,chronic,pain

The wasted version repeats "migraine", "tracker", and "diary" which are already in title and subtitle. The optimized version uses every character on net-new keywords that expand the index.

The Localization Lever Most Apps Miss

Each localization gives you another 100 characters of indexable keyword space. Even if your app is English-only, you can technically use the UK English, AU English, and CA English localizations for additional indexing - though the lift is minimal because Apple deduplicates similar locales.

The real lift comes from genuinely localizing to languages where you have organic interest. A Spanish keyword field gives you full 100 chars of indexing in the Mexican and Spanish App Stores. A Brazilian Portuguese field gives you Brazil. The translation does not have to be of the keywords themselves - it can be local-language search terms entirely.

What to Test Each Release

The keyword field is updateable on every binary release. You should iterate it on every release for at least the first 12 versions of your app. The cycle:

1. Replace the lowest-popularity 2-3 keywords with new candidates
2. Ship the binary
3. Wait 7-14 days for re-indexing
4. Check rank delta in your tool of choice
5. Repeat

This is the cheapest, fastest, lowest-risk ASO experiment available to you. There is no reason not to be running it constantly.

The Hidden Algorithm Shift

In late 2025 Apple tightened how aggressively it auto-extracts keyword variants from titles and subtitles. The practical effect: keyword combinations that used to "just work" because Apple inferred them now require explicit indexing. If your app's organic rank dropped between October and December 2025 without any other change, this is likely the cause - and the fix is a more aggressive use of the keyword field.