The iOS keywords field is a hidden, indexed metadata surface in App Store Connect with exactly 100 characters to spend. Keywords are comma-separated; do not add spaces after commas (that wastes characters). The field is never shown to end users — its only purpose is to add searchable terms to Apple's keyword index for your app.
How Apple combines keyword fields
Apple's search algorithm combines keywords from four fields to build your full keyword index: app title (30 chars), subtitle (30 chars), keywords field (100 chars hidden), and your developer / company name. You don't need to repeat words that appear in another field. Putting "fitness" in your title AND the keywords field wastes 7 characters — fitness is already indexed.
What to put here — the highest-leverage uses of the 100-char budget: - Synonyms that wouldn't fit naturally in visible title / subtitle ("workout", "exercise", "training" beside a "fitness"-anchored title). - Misspellings that real users search ("meditaiton", "yoga", "yogaa"). - Long-tail variations ("HIIT", "Tabata", "stretching", "warmup", "cooldown"). - Related concepts that overlap your category ("mindfulness" for a meditation app, "calories" for a nutrition app).
What NOT to do: - Don't repeat words from title / subtitle / developer name — Apple already indexes them. - Don't add plurals — Apple auto-handles plural variations ("meditation" covers "meditations" too). - Don't use spaces after commas — every wasted character is a keyword you don't have. - Don't add trademarked competitor names — Apple may reject the listing.
Google Play has no equivalent. On Google Play, keywords are extracted from the title (30 chars), short description (80 chars), and long description (up to 4,000 chars). The keyword strategy is different: include high-priority keywords naturally in the long description at roughly 1.5-3% density, repeated 3-7 times depending on length. Less precise than iOS's hidden field, but more flexible.