Free ASO Tool
Check whether your caption renders cleanly at App Store thumbnail size. No signup, no AI calls, no credit cost.
Last updated: May 7, 2026
Paste a draft headline, sub-headline, or caption.
The primary text on screenshot 1. Lands in App Store search results.
Wider devices give captions more thumbnail-rendered headroom.
Estimates rendered font size at the actual width Apple shows in search results, not your design preview.
Pure client-side computation. No credits, no signup, no rate limits.
Different targets for frame 1 headlines, sub-headlines, and general captions.
iPhone 16 Pro Max, iPhone 16 Pro, iPad Pro 13 inch, Samsung Galaxy S25 Ultra.
Drop the headline or caption text into the textarea.
Frame 1 headline rules differ from sub-headline rules. Device width changes thumbnail readability.
Three metrics, each rated pass / warn / fail. Apply the targeted recommendations.
The Caption Readability Checker is a free tool that scores your App Store screenshot caption against three criteria: character count for the field role you're writing (headline, sub-headline, or caption), word count for scan-ability (3 to 7 ideal), and estimated rendered font size at thumbnail width. It returns a pass, warn, or fail rating per criterion plus specific recommendations. No AI, no API call, no signup required. Static client-side check.
Everything you need to optimize your app store presence
No account required • Your data is not stored
For frame 1 headlines, aim for 30 characters or fewer (industry consensus from Apple's own caption examples). For sub-headlines, 50 characters max. Captions longer than 80 characters rarely render readably at thumbnail size in App Store search results. Word count matters more than character count for scan-ability: 3 to 7 words per caption is the sweet spot.
Since the 2025 algorithm update, Apple's OCR reads text inside screenshots and uses it as a discovery signal that reinforces your title, subtitle, and keyword field. Screenshots with readable, keyword-aligned captions rank higher than screenshots with unreadable or generic copy. Captions that fail thumbnail readability at 200 pixels wide effectively don't exist for ranking purposes because the OCR layer also struggles with low-contrast or oversized text.
App Store search results show your first three screenshots at roughly 100 to 200 pixels wide. Most caption tools preview at 600 pixels, so headlines that look great in the preview vanish in actual search results. This tool calculates the rendered font size at thumbnail width based on your chosen device's resolution and flags captions that won't pop. If you only optimize for the desktop preview, you optimize for an audience that doesn't exist.
The Screenshot Copy Generator drafts captions from your feature list. This tool checks captions you already have. Use Copy Generator when starting from scratch or stuck for ideas. Use the Readability Checker when you have a draft and want to verify it actually works at thumbnail size before committing it to your screenshot set.
Frame 1 always needs a caption because it's the first thing every search-result viewer sees. Frames 2 and 3 should also have captions if they're part of the search-result strip. After frame 3, captions become optional; some apps drop them on later frames to let the UI screenshot speak for itself. The 60/40 rule (Apple Review Guideline 2.3.3) applies to UI vs marketing-art ratio, not text vs no-text.
Once your captions pass the readability check, generate a full screenshot set with the AppScreenshotStudio screenshot builder. 10 free credits, no card.
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