The App Store subtitle limit
An App Store subtitle can be up to 30 characters. It appears under the app name on the product page and in search results, and Apple indexes it for search.
How to write a App Store subtitle
Use it for the benefit or the main use case, in words people search for, and do not repeat words already in the name: Apple counts each word once across name, subtitle and keywords.
Questions
What is the App Store subtitle character limit?
30 characters. It is indexed for search, so every character counts.
Should keywords in the subtitle repeat the app name?
No. Repeating a word adds nothing to search; use new words that describe the benefit.
Can I change the subtitle without a new app version?
No. The subtitle changes with a new version submission, unlike promotional text.
Do spaces and emoji count?
Spaces and punctuation count as one character each. This checker counts each visible character once, so an emoji counts as one.
Is my text stored or sent anywhere?
No. The counting happens in your browser and nothing is uploaded.