What is a book blurb?

The shape that works

1. 1A hook, in one line. The promise, or the situation. This is the only sentence most people read.
2. 2Three or four short paragraphs of what the reader gets, or what happens. Short — a wall of text on a phone is a bounce.
3. 3Who it is for, said plainly. “If you have ever…” does more work than any adjective.
4. 4A close that asks for the click.

Non-fiction and fiction want different things

Non-fiction sells the outcome — what the reader will be able to do afterwards. Fiction sells the situation — the character, what they want, and what is in the way. Writing a novel’s blurb as a plot summary is the most common way to make an interesting book sound dull.

On a store page it is also search copy

The description field is indexed, so the words a reader would search for should appear in it naturally. Naturally is the word doing the work — a description stuffed with keywords reads like spam to the human being deciding whether to buy, and they are the one who matters. See book metadata for the fields that are genuinely there for search.