Before we start, yes, yes I know there's another guide out there already. But many modders that I talked to including myself found it somewhat confusing, so I got permission from the original author to write a new one.
Also, please make sure that you have the necessary rights to upload your mod. Simply put, don't upload stuff you don't have permission for.

With that out of the way, let's get started!

• SteamCMD (Download and installation instructions, you can download this to any folder on your PC)
  
• Any text editor (Notepad will do, but I recommend Visual Studio Code for more advanced editing)
  
• Your mod (make sure it works properly)

Later down the line, you will need to log into your Steam account using SteamCMD. Don't worry, it's an official tool by Valve, so as long as you've downloaded it from the link above, your credentials are safe.

This file will tell SteamCMD what to do with your mod.
Make a text file anywhere on your PC and change the extension to .vdf. You can name it anything you want.
Next, open it up in a text editor and paste this in:
Now edit the fields to suit your add-on.

• The App ID determines what game your add-on is meant for. Leave it as is.
  
• The Published File ID is an ID unique to your add-on. SteamCMD will assign that automatically when uploading. If that somehow fails, reset it back to 0 before trying again.
  
• The Content Folder tells SteamCMD where your mod folder (the one with the materials/models/etc. folders inside) is located. You can copy its path by right clicking it in File Explorer and selecting Copy as path. (On Windows 11 you might need to open the extended legacy context menu by hitting Shift + F10.) The backslashes in the path need to be escaped using another backslash in front of them. Additionally, make sure the path doesn't contain any spaces! It messes all sorts of things up. If your path contains spaces, rename the relevant folders or move the file/folder elsewhere. (This also applies to all the other file paths you're going to be using.)
  A good file path looks something like this:
  
  C:\\Users\\yourname\\Desktop\\my_stuff\\steamcmd_upload_guide\\workshop_upload_test
• (Optional, but recommended) The Preview File field is where you insert the path to your thumbnail image. It should be formatted in the same way as the content folder path.
  
• Keep the Visibility field at 2 (Hidden). This allows you to review your add-on in Steam after uploading, giving you a chance to fix any unforeseen mistakes. You can change this setting using the Steam app or website later.
  
• The last three fields are self-explanatory.

You need to open SteamCMD in PowerShell in your mod folder. (The regular command line is also supposed to work, but it didn't for me... Just use PowerShell to be safe.) If you know how to do that, that's great! You can skip this section. If you're not sure, read along.

First thing you'll want to do is open PowerShell in your mod folder. On Windows 11, you can do this easily by right-clicking any empty space and selecting Open in Terminal.
If you're on an older Windows version, or simply don't have this context menu, navigate to inside your mod folder and type "powershell" into the File Explorer address bar, then hit Enter.
If you've done everything correctly, PowerShell should show the directory it's open in like so:
Next, open SteamCMD by pasting the full file path to steamcmd.exe (without quotes) and pressing Enter.
After starting, SteamCMD might download some files that it requires. Let it finish – you'll know when it's ready to receive commands once you see this:

Now it's real hacker time. Log into your Steam account using this command:
Replace "username" and "password" with the appropriate credentials.
If you've got Steam Guard set up, SteamCMD might prompt you for a verification code. Enter it.

Finally, upload your add-on using the workshop_build_item command:
Replace the path with the full file path to your .vdf file, with quotes this time. Again, make sure it doesn't include any spaces.

If all goes well, you should see something like this:

When you're done, you can quit SteamCMD using the quit command.

Now you can view your add-on listing in your browser or the Steam app by pasting your add-on ID (get it from your .vdf file) at the end of this link:
For example, my test add-on link looks like this: https://steamproxy.net/sharedfiles/filedetails/?id=2855833521 (page is hidden)

Here you can add everything that SteamCMD didn't, including images and a description.

And that's it! Just don't forget to set the visibility to Public when you're done.

I hope that this guide helped you save some time, but, first and foremost, thank you for making a mod for Entropy: Zero 2!