TL;DR. 6-9 words. Verb-first. Concrete nouns, no buzzwords. One claim per panel.
Read it at thumbnail size before you ship it. If it sounds like a slogan, rewrite.
Caption-writing for App Store carousels has its own grammar that doesn't translate from
general copywriting. The constraints are tighter: 6-9 words, top-of-panel position, thumbnail
legibility, one screen-of-reading time. Captions written by copywriters used to website hero
sections almost always need a second pass.
The five rules that hold up
1. Length: 6-9 words
Captions under 5 words feel slogany ("Master your money!"). Captions over 10 words wrap
unpredictably at carousel-thumbnail size and the second line often crops. The sweet spot is
6-9 words for single-line captions, or 4+4 for two-line stacked captions.
2. Verb-first
Compare:
Verb-first: "Track every meal you eat." (5 words, action-led)
Noun-first: "Meal tracking made easy." (4 words, marketing-led)
Sentence: "A simple way to track every meal." (7 words, ad-copy-led)
Verb-first reads as product copy — what the app does. The other two read as marketing copy
— what the team selling the app wants you to feel. Product copy converts better in carousel
thumbnails because users scanning the App Store want to know what the app does, fast.
3. Concrete nouns, no buzzwords
The words that flag as filler:
"Powerful" — used so often it's invisible. Cut.
"Seamless" — describes a UX outcome the user can't verify from a screenshot. Cut.
Two-claim panels feel like ad copy ("Track meals AND log workouts"). One-claim panels feel
like product copy ("Track every meal."). One claim per panel converts better and lets each
panel of the carousel make a distinct point. Five panels = five claims = five reasons to install.
5. Read it at thumbnail size before you ship it
Screenshots in the App Store search results render at roughly 1/8 of native size. Captions
that look great at 1320 × 2868 in your design tool sometimes become unreadable squiggles at
thumbnail. Test by zooming out in your editor (or shrinking the preview to ~200 pixels
wide). If you can still read the caption, you're fine.
Caption archetypes that work
Patterns we see consistently in high-performing carousels:
Imperative verb + concrete object: "Track every habit." "Split every bill." "Save without thinking."
Outcome + time qualifier: "Inbox zero before lunch." "All your bills, one tap."
Number-led benefit: "30-second workouts, anywhere." "5 minutes a day."
Negation: "No more lost receipts." "Never miss a refill." (Use sparingly — too many feel preachy.)
Caption archetypes that don't
Adjective stacks: "Simple, powerful, intuitive." Three buzzwords, zero specifics.
Question captions: "Want to save more?" Sales pitch register. Skip.
Sentence captions: "Our app helps you track everything you eat in one place." Too long, too marketing-toned.
Brand-name-led: "Mealmate is the best way to track meals." Users haven't installed yet — they don't care about the brand. Lead with the verb.
Per-locale notes
Caption rules survive translation mostly intact, but watch for:
German + Russian + Hungarian: verbs come at the end of clauses. "Track every meal" reverses to "Jede Mahlzeit verfolgen". The verb is now last, weakening the verb-first punch. Consider rephrasing for clarity in those locales.
Japanese: imperative verbs in formal vs casual register differ. Default machine translation skews formal; app captions skew casual. Hand-review.
Arabic / Hebrew: right-to-left flow. Captions still work verb-first; the visual flow flips but the grammar is the same.