Above the More link
The description is not indexed for App Store search, so writing keywords into it does nothing at all. What it does is convert the person already looking at your page, and it has about three lines to do it in.
Everything after the More link is read by a small fraction of visitors. The first three lines are read by all of them.
The short version
The App Store does not index it.
Above the More link or not at all.
What they get, not why you built it.
Dense blocks are skipped entirely.
It changes without a review.
This is the single most useful thing to know about the field. Apple does not index the App Store description for search, unlike Google Play, which does index its long description. Every hour spent seeding keywords into App Store description prose is an hour spent on nothing.
That is freeing rather than limiting. It means the description can be written purely for the person reading it.
Not indexed. Write it for the reader, not the algorithm.
The product page shows roughly three lines before a More link. Most people never tap it. So the opening has to state what the app does and who it is for, in plain words, immediately.
Lead with the outcome, not the origin story. "Split a restaurant bill between friends in two taps, including tip and uneven shares" earns the tap on More. "We started this app because we love food" does not.
Assume the More link is never tapped. Say the whole thing above it.
Below the fold, short paragraphs and a simple list of what the app does will be skimmed by the people who are genuinely considering it. A dense block will not be read at all.
Keep the awards, the press quotes and the changelog near the bottom. They reassure someone who is already interested and they do not create interest on their own.
The 170 characters of promotional text sit above the description and, unlike everything else, can be changed at any time without submitting a new build for review.
Use it for anything time-bound: a sale, a new feature, a seasonal hook, a fix for something people are complaining about in reviews. It is the only part of your listing that can respond to this week.
170 characters, changeable any day, no review. The only field that can react.
What people ask
No. Apple does not index it for search.
Unlike Google Play, which indexes its long description, the App Store does not use description text for search matching. Your name, subtitle and keyword field carry the search weight. Write the description entirely for the person deciding whether to install.
Long enough to answer the real questions and no longer. The number that matters is the first three lines, which is all most visitors see before the More link. Everything after that serves the smaller group who are seriously considering it.
It is 170 characters above the description that can be updated at any time without submitting a new version for review. That makes it the right place for a sale, a new feature, or a response to something users are currently asking about.
Below the fold, yes, as a short scannable list. Not at the very top, where you need a sentence that says what the app is for. A bullet list as the opening assumes the reader already knows what the app does.
The rest of it
When you want the numbers
The App Rating checker scores any App Store app out of 100 against the leaders in its own category. Free, no account, no card.
ASO Studio