Workshop Addon Creation

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Creating a Workshop Addon

This article will teach you how to prepare and upload an addon to the Steam Workshop.

Before you begin - Rules

There are a few rules before you start uploading addons.

Please see this page for complete set of rules: Steam Workshop Rules

Preparing your addon

To upload an addon to workshop you will need next things:

  • A folder anywhere on your computer containing addon files
  • A 512x512 .jpg icon for your addon.

If you're going to make your addon public, please make sure it's unique and will add something new to Garry's Mod. Don't upload addons you didn't make, even fixed versions, without the author's consent.

Folder with addon files

The structure of addon for Steam Workshop is the same as the classic addon system of Garry's Mod 12, except for those differences:

  • info.txt or addon.txt are not needed
  • You can only upload files that would normally be mounted by the game, except for:
    • .dll, .exe, .htm, .html, .css and .js files are restricted
    • .txt files are restricted too, except for vehicle scripts

You addon folder structure must look somewhat like this: (below is just an example)

NOTE myAddon is the folder you will need to input to gmad.exe or any other Workshop uploader and it's name could be anything, addon's name is defined on the Workshop Page for that addon and NOT by the folder name.

Full file path whitelist can be found here:


addon folder structure.png
Sample Addon is the folder you will need to provide to the gmad.exe.

The icon

This must be a 512x512 JPG image. If gmpublish.exe does not accept your icon, try resaving it with Paint or Paint.NET.

Do not use an image unrelated to your addon - this is stupid and will get your addon removed. Express your addon in image form.
Make it relevant to your addon. Please don't just stitch together something horrible in MS Paint. It should look good, otherwise you'll be making the workshop look dirty. Besides, who wants to download something that looks like a three-year-old made it?


When creating an addon the folder should have an addon.json - which looks like this..

	"title"		:	"My Server Content",
	"type"		:	"ServerContent",
	"tags"		:	[ "roleplay", "realism" ],
	"ignore"	:

title is the name of your addon.

type is the type of addon, one of:


tags is up to two of these:


Ignore is a simple wildcard list of files to ignore. You can have as many of these as you want - and they don't have to be wildcarded, they can be specific files.

Creating a .gma for upload

For Windows, you can simply navigate to your GMad.exe in <STEAM LOCATION>/steamapps/common/garrysmod/bin and drag'n'drop your addon folder ( myAddon in this example ) onto GMad.exe.

GMad.exe will now create your .gma. It will place it to the same location where your folder is, with the same name.

Do not move GMad.exe anywhere!

Alternatively You can open the command prompt (cmd.exe), cd to the gmod bin folder
(cd "<STEAM FOLDER>/steamapps/common/garrysmod/bin", include quotes), then enter the following command (including quotes):

gmad.exe create -folder "<FULL PATH TO ADDON FOLDER>" -out "<FULL PATH TO OUTPUT .gma FILE>"

Windows users can also create a .bat file to automate this process:

"C:\Program Files (x86)\Steam\steamapps\common\garrysmod\bin\gmad.exe" create -folder %1

Just make sure to insert correct path to your GMad.exe.

Common Errors

[Files does not pass whitelist]

You have either dragged a wrong folder onto GMad.exe, or your addon contains forbidden files. See above.

Uploading your addon

There are multiple ways of doing that, we are going to cover only the most convenient way of doing this, if you are on Windows.

At this point you should have a .gma file and a .jpg file. For the sake of making this easy, rename both files to have the same name, for example myaddon:

  • myaddon.jpg
  • myaddon.gma

Next you want to navigate to your gmpublish folder and create a .bat file there:

gmpublish.exe create -addon %~n1.gma -icon %~n1.jpg

Save it as something like gmpublish_create.bat.

Once you got the .bat file ready, simply drag'n'drop your .gma or your .jpg onto that .bat file. It is essential that both files must have the same name.

Now gmpublish.exe will go through the process of compressing and uploading the addon to Steam Workshop.

Once that process is completed, open your Garry's Mod Steam Workshop, go to "My Shared Files" ( You can also get there from your profile ) and change visibility of your addon to Public.

You are done. Your addon is now live. You can now change the title, description, images and videos for your addon.

Note that rules also apply to your title, description, images, icon and videos:

  • No questionable content
  • No racism or offensive language/material

Common Errors

Compression Failed

This is simple - your addon is too big. This is usually solved by downscaling your .vtf textures. Note that some video cards may not even support 4096x4096 textures! 1024x1024 or 512x512 are usually more than enough.

Ran out of quota

If this happened to you, contact me at

Here is a list of other error numbers and their descriptions.


You can use alternative tools made by community members to create, extract and upload addons to Steam Workshop.

Links to such known tools: ( feel free to expand )

After Going Live

Please make sure your addon isn't creating errors for people. If your addon is creating too many errors it will be removed.

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