For the most part, this is what I think is within the bounds of what's appropriate.
Profanity: Use this tag if characters use any word at all you wouldn't want a 6-year-old to hear.
Gore: This term involves anything other than blood that's supposed to be on the inside getting exposed to the outside. However, you might want to also add it if there's just an excessive amount of blood. Graphic and evocative descriptions of even shallow wounds, swelling, or broken bones (that don't pierce the skin) would count as well.
Sexual content: Any and all on-screen sex and strongly hinted off-screen sex should earn this label. I'd say the bottom threshold for this tag would be mentions of "flower offerings" in Ascendance of a Bookworm. (Absolutely no sex was shown on scene or even close to being on scene in that series until a certain point in part 5, but there are a number of mentions that make it clear enough it's taking place very far off-screen if you can cut through the euphemisms.)
If your content is below those thresholds then you probably don't need the tag. Whether or not you put it there anyway is entirely up to you whether you prefer to error on the side of caution and not wanting trigger-happy complainers or on the side of not wanting to scare away anyone who would avoid it just for having that tag.
In my Key to the Void series, I have mentions that acknowledge sex and rape are things that exist in the world, up to and including going past the point where it can be called an implication that the MC is a child of rape, but even off-screen sex does not come anywhere even close to any scene in the story so I do not have a "sexual content" tag.
That is precisely the problem that arises for me, if I put the label on it, it could be thought that it is a story, let's say "Mature" and make people who like calmer fantasy stories with some fights skip it.
Because the story itself if I wanted to explain it somehow is somewhat strange.
The story is immature, because that is the nature of the characters, not so much of the world, the world has its good and bad nuances, they have more background, let's say it towards characters who know the bad things there are, but they have decided to act and live accordingly. a more innocent way, making jokes between them and simple things let's say that this is the attitude that there is the most in history.
But the time comes to fight against an enemy that brings death, the characters always have their benevolence when speaking and acting, the use of derogatory words and of that kind will never come from the main characters, but against an enemy, those parts of the story They resort to spicological threat.
In fights the protagonist gets his stomach pierced and vomits a large amount of blood, he is fighting to the death against an enemy and the details of the cruelty of the battle are given, large-scale elimination of enemies with explosions.
He is fighting under a great pressure of fear, for the being that is in front of him that is not just an irrational monster, it is a being that you as a reader are afraid of, the classic bring death to all beings just for pleasure.
Some situations where the protagonist's morality is questioned, who within his immature way of acting is quite mature.
But as I said, these situations are so rare that we can say that they are the peaks where the story changes completely from the tone of the other 80% of the work to something calmer, innocent but with action.
I'm thinking that in order not to use the labels, I'll just reduce the reported details and use some kind of inferences or hints to explain what shouldn't be said explicitly.
That, or give two chapters, one where I take my liberties with the details, and another where the quality of the narrative is not lost at all but I offer something less detailed.
