https://e621.net/post/show/1893389 for example

You cannot. Aliases and implications are done in the background and only the end results stay. As invalid tags are aliased into invalid tag, it could be any one of the tags aliased.

You can however use new upload form and after done tagging, press Preview Final Tags to see if any one of the tags is being aliased to invalid before hitting upload.

I'll do that, thanks. Isn't that kind of counter-productive though?

Also I found out what it was; fauxhawk. Fix it if you want, not sure how. It's a hairstyle and should be valid i believe.

FurZ said:
I'll do that, thanks. Isn't that kind of counter-productive though?

Earlier we had absolutely nothing, so "it's better than nothing".

The main reason for invalid tag is to get rid of tags that should not exsist but are still constantly tagged. This way nobody has to constantly go trough list of tags just to go on posts and get rid of them and now they are neatly just single tag which is easy to untag in mass. This include subjective tags like cute and tags which are assumed by default and have exclusive tag like open_eyes and closed_eyes. As neither of these should've been in the post to begin with, it's better to just not have them, but we cannot delete tags automatically.

Ideal situation is to use Wiki and Tags pages found in top panel to make sure that tags are in use and what situations the tags should be used.

So e.g. with cute, instead you might want to tag stuff like chibi or big_eyes.

Stuff that's more easily sorted, there's disambiguation. That means the tag you did will be aliased to tag with (disambiguation) at the end. At this point you can open the wiki article and see the tags that are in use which you might've meant.

e.g. from_behind_(disambiguation), you should instead use from_behind_position if you meant the sex pose with penetrating partner is behind the receiver and rear_view if you meant that the camera angle is pointing at characters back.

FurZ said:
Also I found out what it was; fauxhawk. Fix it if you want, not sure how. It's a hairstyle and should be valid i believe.

Looking at fauxhawk wiki page, that tag is valid and not aliased to invalid tag, so you are mistaken.

E: Also your sourcing is kinda lacking and you are uploading inferior copies of images.

I dont see another source for his images and im logged in to twitter so im getting the higher res images. Also i have no idea what's causing the invalid tag then.

FurZ said:
I dont see another source for his images and im logged in to twitter so im getting the higher res images.

Twitter is low res to begin with.

I see. So many artists with only twitter as a source for their art. Shitsucks.

FurZ said:
I dont see another source for his images and im logged in to twitter so im getting the higher res images. Also i have no idea what's causing the invalid tag then.

That post was higher quality on artists gallery.
Also even if you got those from twitter, your uploads source field is completely empty. No link to tweet, no link to direct image.

AoBird said:
Twitter is low res to begin with.

Wrong. Twitter is high resolution, but also high compression.

So if artist uploads 4000x4000 PNG in both twitter and furaffinity, twitter would be 4000x4000 JPG where furaffinity would be 1280x1280 JPG with incorrect PNG extension in filename.

Well, the invalid tags all end up in it's wiki, so you could look threw it if you really wanted to, to see if you recognize one of the tags you tried to adc