iOS App Keywords: Rules, Limits & Optimization Tips

The iOS keyword field is one of the most powerful — and most frequently misused — tools in App Store Optimization. Apple gives you exactly 100 characters of hidden metadata to tell the algorithm what searches should surface your app. Every character counts. Every wasted character is a missed opportunity to rank for a valuable search term.

Unlike Google Play, where your description is indexed for search, the Apple App Store relies primarily on three text fields for search ranking: your app name (30 characters), subtitle (30 characters), and the keyword field (100 characters). That's just 160 characters total to capture every relevant search query. Mastering the keyword field is essential for iOS ASO success.

This guide covers every rule, limit, and optimization technique for the iOS keyword field.

How the iOS Keyword Field Works

The Basics

• Location: App Store Connect → App Information → Keywords
• Character limit: 100 characters per localization
• Visibility: Hidden from users — only the algorithm reads it
• Format: Comma-separated terms (no spaces after commas)
• Update frequency: Can only be changed when submitting a new app version
• Impact: Directly determines which searches surface your app

How Apple Uses Your Keywords

Apple's search algorithm builds a keyword index from three sources:

1. App name (30 characters) — highest weight
2. Subtitle (30 characters) — high weight
3. Keyword field (100 characters) — moderate weight

The algorithm combines words from ALL three fields to create keyword combinations. A word in your title can combine with a word in your keyword field to create a two-word phrase that you rank for.

Example:

• Title: "FitTrack: Workout Planner"
• Keyword field: "gym,routine,exercise,log,strength,cardio"
• You can rank for: "workout log," "exercise planner," "gym routine," "strength workout," "cardio exercise" — combinations across fields

This cross-field combination is the key to maximizing your 100 characters.

Rules and Restrictions

Apple's Official Rules

Undocumented Behaviors

Through extensive testing, the ASO community has identified additional behaviors:

Apple auto-indexes:

• Your developer name
• Your app's category and subcategory
• Common variations of words in your title/subtitle
• Plural forms of singular keywords

Apple does NOT index:

• Your app description (unlike Google Play)
• Your "What's New" text
• Your promotional text
• In-app purchase names (these have their own search index)

Cross-locale indexing:

• Keywords from your English (US) localization may contribute to rankings in other English-speaking markets
• Some developers report that keywords in one locale affect rankings in related locales
• This behavior is not consistent and shouldn't be relied upon

Character Optimization Strategies

Strategy 1: Eliminate Waste

Every character matters. Common wastes:

Before optimization (68 useful characters out of 100):

budget tracker, expense tracker app, money management, financial planning apps, savings

After optimization (96 useful characters out of 100):

expense,money,management,financial,planning,savings,spending,bills,income,debt,personal,finance,daily

(Assuming "budget" and "tracker" are already in the title)

Strategy 2: Single Words Over Phrases

The keyword field is most efficient when filled with individual words rather than phrases, because:

1. Apple combines words from the keyword field with words from your title and subtitle
2. A phrase like "budget tracker" uses 14 characters for one combination
3. Individual words "budget" and "tracker" use 14 characters but enable dozens of combinations with other words in your fields

Exception: Include multi-word phrases only when the individual words wouldn't combine to form the phrase (rare) or when the phrase has significantly higher search volume than any combination.

Strategy 3: Maximize Unique Words

Count unique words, not total characters. More unique words = more search combinations:

Fewer unique words (poor):

budget tracker,expense tracker,money tracker,spending tracker

→ Only 5 unique words: budget, tracker, expense, money, spending (tracker repeated 4 times)

More unique words (better):

budget,expense,money,spending,savings,bills,income,debt,personal,finance,daily,weekly,monthly,log

→ 14 unique words, each combinable with title/subtitle words

Strategy 4: Include Competitor Names

Controversial but effective. Adding competitor app names as keywords can surface your app in searches for those competitors.

Considerations:

• Apple may reject if the competitor files a trademark complaint
• Use this strategically for 2-3 top competitors, not all of them
• Your conversion rate will be lower (users were searching for someone else)
• Monitor for rejection — be prepared to swap in alternative keywords

Strategy 5: Include Misspellings and Abbreviations

Users misspell search queries regularly. Including common misspellings captures this traffic:

• "calender" (common misspelling of "calendar")
• "excercise" (common misspelling of "exercise")
• "fittness" (common misspelling of "fitness")

Also include:

• Abbreviations: "calc" for calculator, "mgr" for manager
• Acronyms: "HIIT" for high-intensity interval training
• Slang: terms users actually use vs. formal terms

Keyword Research Process

Step 1: Seed List Generation

Create a comprehensive list of potential keywords:

1. What does your app do? List every function, feature, and use case
2. How do users describe it? Think in user language, not developer language
3. What problems does it solve? Problem-oriented keywords often have high intent
4. What are users searching for? Check auto-complete suggestions in the App Store
5. What do competitors use? Analyze competitor titles, subtitles, and rankings

Step 2: Volume and Difficulty Assessment

For each potential keyword, assess:

Step 3: Prioritization Matrix

Plot keywords on a 2×2 matrix:

High Volume + Low Difficulty = PRIMARY TARGETS (fill these first)
High Volume + High Difficulty = ASPIRATIONAL (include if space allows)
Low Volume + Low Difficulty = LONG-TAIL (fill remaining space)
Low Volume + High Difficulty = SKIP (not worth the characters)

Step 4: Field Allocation

Distribute your best keywords across all three indexed fields:

1. Title (30 chars): Your #1 keyword phrase
2. Subtitle (30 chars): Your #2 keyword phrase
3. Keyword field (100 chars): Everything else, prioritized by value

Remember: words DON'T need to be repeated across fields. A word in the title combines with words in the keyword field automatically.

Step 5: Fill and Count

Fill the keyword field with prioritized single words:

[highest priority word],[second priority],... [lowest priority to fill remaining space]

Count characters carefully. If you have 3 characters left, find a 3-letter keyword to fill them (e.g., "log," "app" — wait, not "app"). Every character should contribute.

Localization for Additional Keywords

The Localization Strategy

Apple allows different keywords for each localization. This means you can effectively multiply your keyword coverage:

Primary localization (e.g., English US): Your main 100 characters
Secondary localizations: Additional 100 characters each

For English-speaking markets, the keywords from your English (US) localization often contribute to rankings in English (UK), English (AU), English (CA), etc. But adding unique keywords to those localizations can expand your coverage.

High-Value Localizations

Localization Tips

• Don't just translate your English keywords — research what users actually search for in each language
• Some English words rank in non-English markets (tech terms, brand names)
• Use native speakers to identify natural search terms vs. literal translations
• Prioritize localizations by market revenue potential

Common Mistakes

Mistake 1: Not Using All 100 Characters

Many developers leave 20-40 characters unused. That's 20-40% of your keyword potential wasted. Fill every character.

Mistake 2: Repeating Title/Subtitle Words

Words in your title and subtitle are already indexed. Repeating them in the keyword field wastes characters without ranking benefit.

Mistake 3: Using Phrases Instead of Single Words

"budget tracker" in the keyword field uses 14 characters for one combination. "budget,tracker" isn't needed if both words appear across your fields separately.

Mistake 4: Including Spaces After Commas

"budget, tracker, money" = 22 characters (2 wasted on spaces)
"budget,tracker,money" = 20 characters (0 wasted)

Mistake 5: Never Updating Keywords

Keywords that don't rank after 4-6 weeks should be replaced. Search trends change. Competitors optimize. Your keyword field should evolve monthly.

Mistake 6: Ignoring Long-Tail Keywords

High-volume keywords are competitive. A mix of high-volume targets and low-competition long-tail keywords ensures you rank for something immediately while building toward harder targets.

Mistake 7: Not Tracking Rankings

If you're not tracking which keywords you rank for and at what position, you can't optimize. Use an ASO tool to monitor rankings weekly.

Measurement and Iteration

Weekly Tracking

Track rankings for your target keywords every week:

When to Change Keywords

Replace a keyword when:

• No ranking improvement after 4-6 weeks
• The keyword has no measurable search volume
• You find a higher-volume alternative for the same character cost
• A seasonal keyword's season has ended

Keep a keyword when:

• Ranking is improving week over week (even slowly)
• You rank in the top 20 (within striking distance of page 1)
• The keyword drives measurable installs despite lower volume

The Optimization Cycle

Research → Implement → Track (4 weeks) → Analyze → Swap losers → Repeat

Each app update is an opportunity to refresh your keyword field. Plan keyword changes alongside your regular release schedule.

Advanced Tips

Compound Word Hacking

Some compound words can be split to create more combinations:

• "workout" → if "work" and "out" are both useful keywords separately, they take the same space but add more combinations
• Be careful: not all compound words are indexed as their component parts

Seasonal Keyword Rotation

Rotate seasonal keywords based on the calendar:

• January: "resolution," "goals," "new year"
• Spring: "spring," "outdoor," "fresh"
• Summer: "vacation," "travel," "summer"
• Fall: "school," "organize," "autumn"
• December: "holiday," "gift," "christmas"

Plan these rotations in advance and submit app updates to coincide with seasonal peaks.

Competitor Keyword Monitoring

Track what keywords your competitors rank for that you don't. When a competitor adds a new keyword to their listing, evaluate whether you should target it too.

Conclusion

The iOS keyword field is 100 characters of pure opportunity. Every character should be intentional — researched, tested, and justified by data. The developers who treat keyword optimization as a discipline, updating and refining their field with every app release, consistently outrank those who fill it once and forget it.

Start with thorough research. Fill all 100 characters with unique, single-word keywords that complement your title and subtitle. Track rankings weekly. Replace underperformers monthly. And remember: in the Apple App Store, your keyword strategy is your visibility strategy. Master it, and you unlock a sustainable stream of high-quality organic installs that no amount of paid advertising can replicate.