The iOS subtitle is a keyword-weighted field introduced with iOS 11 (September 2017). It's a separate 30-character text field that appears directly under your app name on the search results page and product page, and its keywords are indexed with high relevance — generally just below title and above the hidden keyword field.
Real catalog patterns (MWM App Store listing scrape, US): 69% of measurable iOS apps fill the subtitle field. Among those that use it, the median length is 27 of the 30 available characters — apps treat the subtitle as prime keyword real estate and spend nearly the whole budget.
The length distribution makes the behavior obvious: the mass sits in the 26-30 character band, right against the hard cap. Very few apps use a short subtitle — it's all-or-nearly-all. If your subtitle is short or empty, you're under-using the second-most-keyword-weighted field on the App Store, which is one of the most common and most fixable ASO gaps.
iOS subtitle adoption + median length by category (US)
| Category | Subtitle adoption | Median length |
|---|---|---|
| Lifestyle & Well-being | 59.1% | 27 chars |
| Productivity & Tools | 64.5% | 27 chars |
| Game | 90.2% | 27 chars |
| Education & Knowledge | 69% | 27 chars |
| Media & Entertainment | 77% | 27 chars |
| Social & Communication | 68.3% | 27 chars |
Adoption varies sharply by category. Games fill the subtitle 90% of the time — for them it's a core keyword surface — while Lifestyle apps trail near 59%. But every category lands at a 27-character median: once an app commits to the subtitle, it uses essentially all of it.
Subtitle as secondary tagline — the common pattern: the title carries your primary keyword and brand, the subtitle carries 2-3 secondary keywords phrased as a benefit ("Track Habits, Meditate, Sleep" for a wellness app, "Photo Editor, Filters, Effects" for a photo tool). Commas are valid separators and don't waste indexation — Apple's algorithm treats each comma-separated phrase as a distinct keyword chunk.
Google Play equivalent: Google Play doesn't have a direct iOS-subtitle equivalent. The closest parallel is the short description (80 characters), which is visible on the listing AND keyword-indexed — see the [[short-description]] entry. The two fields have different lengths and slightly different conversion roles, so they're optimized separately per platform.