How to Create a Font

Place the Font File in Your Addon

When Garry's Mod loads fonts, it looks for them in the /garrysmod/addons/{Your Addon's Folder}/resource/fonts/ folder.
Example: resource/fonts/arial_bold.ttf

Due to inconsistencies between operating systems, it's good practice to ensure that your addon's files and folders (including font files) use entirely lowercase names which do not contain spaces. Spaces should be replaced by underscores (_) or hyphens (-).
This is especially true on Linux.

Note: All fonts must be in the .ttf format.

In addition, make sure that the font's .ttf file is available clientside, otherwise players will not be able to use it.
You can do this via resource.AddSingleFile

Find the Font's Name

To use your font in Garry's Mod, you need to know the name of your font. This is required for surface.CreateFont.

The font name is not the .ttf file's file name. Instead, the .ttf file has the name of the font embedded within it. This embedded name is what Garry's Mod uses to create the font and make it available in-game.

Windows

1. Right click on your .ttf font file and click Preview

2. In the window that opens, find the line that begins with "Font name"

3. The name you will need to use in Garry's Mod is the text following "Font name"
   In the example below, the name is Digital-7 Mono

MacOS

Linux

GNOME Font Viewer

Package name: gnome-font-viewer

1. Open the font

2. Find the label at the center of the top menu (In this example, it's Arial, style is not a part of the font here)

3. Additionally you can check the font name by click Info on the top menu and find Name:

Creating the Font

For information and examples on how to use the font you have now installed and found the name of, see surface.CreateFont