There any need for the peaceful tag? I get that it's conveying a sense of serenity and calm, but that could apply to thousands upon thousands of pics on Danbooru, never mind that it's heavily subjective. It's just like when I brought up the love tag in forum #82985 - the tag is vague, and the posts are a total mess.

some of the posts can fall to resting / relaxing and happy (?) instead.

other similar peaceful-like tags in use are calm and serene. not sure what to do with them.

I'd say not to use the tag at all. "Peaceful" is definitely too broad for how we tag.

For that matter, I think all of the tags ghostrigger mentioned save happy can go as well. For the most part, they can be covered by more concrete tags like sleeping, lying, leaning back, closed eyes, smile, etc.