I’m not a fan of spoilers in book descriptions or reviews.
Having said that, I can see they might sometimes be needed in a review.
Book Descriptions
In general, I think the book description should introduce the main characters and the central plot. That’s it. The book description shouldn’t give spoilers about what’s going to happen later in the book. In my view, anything that’s mentioned in the book description should occur in the opening chapters.
(Otherwise, I find myself skimming as I wait for the promised events.)
Book Reviews
Book reviews are a little different. While I don’t want to read (or write) spoilers in book reviews, there are times when they are unavoidable.
A good review will share the basic plot, but should also share something of the reviewer’s emotional response to the book. That can be hard to do without giving spoilers …
One difficulty comes in defining what is actually a spoiler. Some novels contain content that some readers would prefer to know about in advance so they can make an informed decision as to whether they want to read the book or not. Other readers dislike content warnings or trigger warnings as they can be spoilers.
For example, I recently read and reviewed a historical romance where the heroine was married against her will, and the husband consumated the marriage. We call that rape now, but the act was not considered rape in the laws of the time. All the same, a modern reader may well want to be aware of the fact … but it’s two spoilers (saying she was married, and saying the marriage was consumated).
Some novels include references to historical events. If a reviewer mentions that, say, the Titanic sank or the Germans lost World War One, is revealing that a spoiler or is it general knowledge?
My knowledge of history is centred around the history of English-speaking and European countries. A Japanese or Indian reader would have a very different knowledge of history. What about lesser-known historical facts, or historical facts that are common knowledge in other countries but unknown to the reader? Is it a spoiler simply because I didn’t already know about it?
Goodreads allows reviewers to tag some or all of their review as containing spoilers, and hides that part of the review. This is a nice compromise. Those people who want to know the spoiler can read the full review, and those who don’t want the spoiler don’t have to read it.
I do not like spoilers in book reviews or on the back of the cover. I recently read a review that said “at the end…this happened.” I couldn’t believe they had put the details in, it was a big spoiler and they hadn’t marked it as such. I do want a trigger warning for certain things, and some might consider them spoilers, but if it says this book mentions suicide, I don’t feel like that is a spoiler since it is vague, but it’s enough of a trigger warning. Hopefully, that makes sense.