The tumbler page where I got the Floatzel art of Barnabe include some hints to his story in the tags. I wondered of this is something e621 would refrain its users from doing.

I'm confused about this post.

Tags on site should only match what's in the image, not "story" info outside what's currently seen.

There's no restriction on people's comments if that's what you mean though.

We tag what we see, not what's been hinted to happen later. I can't think of any case where something you could see in an image would qualify as spoilers for later.

OP is referring to a post's tags on Tumblr, not on e6. Those tags should not be used on this site, you should just tag what you see as per policy. You can put the artist's comments and/or Tumblr tags in the description.

^ preferably in a somewhat sentencey way. (at least personally, just putting something like 'tumblr tags: foo bar baz' seems like it could invite unwanted "help" [transferring those tags to the post] from newbies)

leomole said:
You can put the artist's comments and/or Tumblr tags in the description.

Yeah... I'd say that description field isn't meant for sharing another site's tags. It's more for official descriptions/stories. Sometimes other stuff, but can't think of a case where a list of tags makes sense.

Wodahseht said:
I'd say that description field isn't meant for sharing another site's tags.

I mean Tumblr tags like what OP's asking about, stuff like #andthentheyalllivedhappilyeverafterexceptforthatthingwiththeasteroidsbutwedonttalkaboutthat.
Sometimes artists do that because they think it's cute. If you can translate that into something human-readable, it might be worth putting in the description.

Copy it into the description, or a comment.