I should have made this a separate thread. How To Write Costumes in a screenplay: https://twitter.com/vivaciousvandal/status/1254609897552928768

You have already been told to keep your descriptions brief, but maybe not explained why.
Partly it is to make your script faster to read so it doesn’t scare anyone off.
The other part is so that when it is produced you don’t have to fight me in a cage match.

(And in my experience this also applies to Art Department.)

In an ideal set, all your department heads know more than you do about their department. So you don’t need to dictate to them!

For me, trends change fast, or another movie/show may have your exact outfit already and you didn’t catch the similarity. Some clothes are too pricey...

The actor may not be comfortable in that cut, or look awful in that color... there are a million and one reasons a department head may not want to execute your exact vision.
So how do you write something specific enough to picture and vague enough to be flexible?

Well, let’s play a game.
How would you describe this look?

All great suggestions!
Someone just staring out would probably over describe: “black and red plaid layered shirts with studded gloves and dark eyeliner” is a huge waste of space for what you each managed in about 3 words.

Harder one:
How would you describe this Iris Van Herpen look?

The key things here are:
Futuristic (3D printed to be exact)
Sculptural (doesn’t follow the lines of the body)
Animatronic (or otherwise moving on its own)
Reminiscent of an alien or giant spider

You COULD mention the color in the way that it is unexpectedly light for something so evil, but it’s probably Unnecessary unless there is context you want to give in the script.

You could describe it as
Part woman, part giant arthropod
The MET gala’s spider gown
A woman wearing the eyes and legs of a giant robotic spider
A dress depicting the recurring nightmare you had after watching Aracnaphobia

Small formatting tips: a longer description is okay the very first time you meet a character or if they change into a scene-specific look like an event gown or an undercover spy costume. Besides that ask if you even need a description at all?
As with all other things, your genre-

Should also factor in to how you describe clothes. If it’s a comedy you can do a funny one-liner roast of the outfit.
Some people hate non-dialogue jokes but I enjoy them. I have to spend several hours rereading and breaking a script. I like to enjoy it!

If it’s horror, you can scare me.
“Future arachnid dress” covers it, but I’m not afraid.
“When she looks away, her gown still watches him and clicks its pincers” makes me shiver.
I don’t need to know that there are legs on her shoulders and eyes on her torso. I can invent that!

I could go back through the scripts that have over-described costumes to me.
One called for a specific out-of-style suit with suspenders that the directors ended up totally changing. All that really mattered for that scene was that the guys were peacocking and really overdoing it

Another called for heels that the actress couldn’t walk in.

There are so many unknowns before someone is cast (coloring, ears pierced or not, length of hair, etc) that there really is no point in writing down the exact look that you imagine.

This is the only important tweet in the thread:

I say this as someone who has dedicated their professional career to clothes:
telling me what a character is wearing is useless.
Tell me what that outfit SAYS ABOUT THE CHARACTER.

I don’t care if he’s dressed sloppily, tell me he’s wearing yesterday’s clothes because he slept in his office.
I don’t care if she’s wearing the outfit from The Wizard of Oz (unless she’s a celebrity impersonator), tell me that she is as innocent as a picnic and dressed to match

Don’t tell me the components of an outfit, tell me the character’s motivation for putting it on this morning. Tell me what event it looks like they’re heading to. Tell me if their whole closet is just this one look repeated. Tell me it’s hand-me-downs, or so new the tag’s on.