App Store keyword field packer

What the packer does to each list

1. Splits phrases into words (you can turn this off). App Store search combines the words of one localization, so habit tracker costs fewer bytes as habit beside a name that already says tracker.
2. Drops words already in that localization's name or subtitle. Apple: “Your app is searchable by app name and company name, so you shouldn't duplicate these values in the keyword list.”
3. Drops words another localization above it already holds, for localizations the chosen country reads. Which ones it reads comes from the planner's data.
4. Folds English plurals (counters → counter) and drops duplicates, filler words such as app, free and the, and common short words in French, German, Spanish, Italian, Portuguese, Dutch, Swedish, Danish, Norwegian and Polish.
5. Flags keywords of one or two characters. Apple's reference asks for keywords “each greater than two characters”.
6. Flags names of well-known apps, companies and other platforms from a fixed list, as a prompt to check. Apple: “Names of other apps or companies aren't allowed.” It is not a legal opinion.
7. Packs in your order with commas and no spaces, and stops at 100 bytes. A word that does not fit is listed, and a shorter word further down can still take the space.

Bytes, not just characters

In UTF-8, English letters take 1 byte, most accented Latin, Greek, Cyrillic, Hebrew and Arabic letters take 2, and Chinese, Japanese, Korean, Thai and Devanagari characters take 3. So 100 bytes holds about 50 Russian letters or 33 Japanese characters. The meter shows both counts. Apple's two pages disagree on the unit; our guide quotes both.

Questions

How long is the App Store keyword field?

Apple's App Store Connect reference says “up to 100 bytes”; its product page guide says “100 characters”. In English the two are the same. In languages with 2- or 3-byte letters they are not, so the packer fits 100 bytes, the stricter reading.

Should I put spaces after the commas?

No. Apple's guide says terms are “separated by commas and no spaces”. A space costs a byte you could spend on a word.

Should I repeat words from my app name?

No. Apple's reference says your app is already searchable by its name and company name, so “you shouldn't duplicate these values in the keyword list”. The packer drops those words.

Do I need plurals?

Apple's guide advises against “Plurals of words that you’ve already included in singular form”. For English localizations the packer folds plurals to one form.

Why drop words another localization already has?

A country's search reads several of your localizations. A word already in one of them counts there; a second copy in another localization the same country reads adds nothing. Our probe study measured which localizations each country reads.