First, thanks for the reader; it's amazing, and I love it.

That said, consider for example this page:
http://dynasty-scans.com/reader/series/flower_flower

See that tag on chapter 13? Do you see how that can be considered a (major) spoiler?
So okay, the tagging could be trollish, or not represent exactly what it looks like, or something, but still.

So my suggestion would be to hide tags by default, at least on the http://dynasty-scans.com/reader/series pages. Actually, even on the "recent releases" page it can still spoil a lot.

Again, your reader is awesome, and this is a minor point. Also, sorry if this has already been debated.

It's been removed.
This is something that we're very much willing to accommodate: if a series/chapter needs tags added or removed and it's a good fit then we'll oblige. We do not want spoiler tags, although tags of interest is something we do want to keep throwing in. It's a back and forth thing.
Thanks for the heads up.

Cool, thanks!

Who does the tagging by the way? You, or users? (Basically, how likely are other chapters to be tagged like this?)

In general, I think that the "kissing", "nsfw" and "almost nsfw" will always be spoilers, at least in series (a sudden nsfw tag at chapter 10 would be a spoiler, while a one shot tagged nsfw is something pretty usual). IMHO, "kissing" would be a spoiler even in a one shot: it distinguishes between good and bad ending one shots, bad ending being relatively common.

I'm sure there are a few other spoiler tags. I'm sure you don't have anything as blatant as "confession" or "death", but maybe "NTR"?

Another possibility would be to not display any tag for individual chapters, only those for the serie as a whole, thought that might be too strict.

Usually whoever uploads whatever it is decides on the tags first, but anyone with reader access can modify the tags post-upload. Lililicious and Yuri Project upload their own stuff themselves, while anything else is typically uploaded by a Dynasty member.