Creating a new project

This assumes:

• Minecraft is installed
• Running on macOS
• IntelliJ IDEA is installed

I'm going to use ~/dev/simple-mod as the location for the mod files, and simplemod as the name of the mod, in the org.lorinhochstein.simplemod package.

Download the Mod Development Kit

1. Go to http://files.minecraftforge.net/ and in the "Download Recommended" box, click the icon labeled "Mdk".

2. You'll likely get some horrible popup asking you to to download a new media player or somesuch. Cancel that download.

3. Click the red SKIP button in the top right-hand corner.

4. Download the file, should be named something like forge-1.8.9-11.15.1.1722-mdk.zip

Create a git repo, unzip the files and commit it

mkdir ~/dev/simple-mod
cd ~/dev/simple-mod
unzip ~/Downloads/forge-1.8.9-11.15.1.1722-mdk.zip
git init
echo classes >> .gitignore
git add .
git commit -m 'initial commit'

Modify build.gradle

Here are the changes I made:

diff --git a/build.gradle b/build.gradle
index 8b83723..382a6bb 100644
--- a/build.gradle
+++ b/build.gradle
@@ -21,8 +21,8 @@ plugins {
 }
 */
 version = "1.0"
-group= "com.yourname.modid" // http://maven.apache.org/guides/mini/guide-naming-conventions.html
-archivesBaseName = "modid"
+group= "org.lorinhochstein.simplemod" // http://maven.apache.org/guides/mini/guide-naming-conventions.html
+archivesBaseName = "simplemod"

 minecraft {
     version = "1.8.9-11.15.1.1722"

Download artifacts needed for decompiling and building

./gradlew setupDecompWorkspace

Open the project in IntelliJ IDEA

idea .

1. Brings up the "Import Project from Gradle" dialog.
2. Click "OK" at bottom-right.

Create run configuration

Exit IntelliJ IDEA, then do:

./gradlew genIntellijRuns

Configure run configuration

1. Launch IntelliJ IDEA loaded with the project
2. In the "Run configurations" dropdown at the top-right of IDEA, cilck on the down arrow and choose "Edit Configurations..."
3. Choose "Minecraft Client" in the left-hand pane
4. For "Use classpath of module", click the dropdown and choose "simple-mod_main"

Once this is done:

1. Click "OK" to dismiss the dialog
2. Run the "Minecraft Client" configuration.

This should load Minecraft.

Verify the mod loaded properly

1. Click the "Mods" button in the Minecraft dialog.
2. Choose "Example Mod" in the scroller on the right

Dialog should look like:

Customize the metadata

See also official docs on FML mod information file.

Edt src/main/resources/mcmod.info. Mine looks like:

diff --git a/src/main/resources/mcmod.info b/src/main/resources/mcmod.info
index f480667..53350db 100644
--- a/src/main/resources/mcmod.info
+++ b/src/main/resources/mcmod.info
@@ -1,14 +1,14 @@
 [
 {
-  "modid": "examplemod",
-  "name": "Example Mod",
-  "description": "Example placeholder mod.",
-  "version": "${version}",
-  "mcversion": "${mcversion}",
+  "modid": "simplemod",
+  "name": "Simple Mod",
+  "description": "A simple mod example",
+  "version": "1.0",
+  "mcversion": "1.8.9",
   "url": "",
   "updateUrl": "",
-  "authorList": ["ExampleDude"],
-  "credits": "The Forge and FML guys, for making this example",
+  "authorList": ["Lorin Hochstein"],
+  "credits": "",
   "logoFile": "",
   "screenshots": [],
   "dependencies": []

Create Java package and file

We need an org.lorinhochstein.simplemod.SimpleMod Java class.

1. View > Tool Windows > Project
2. Expand simple-mod > src > main > java
3. Right-click on java
4. New > Package
5. Type org.lorinhochstein.simplemod and click OK
6. Right-click on org.lorinhochstein.simplemod
7. New > Java Class
8. Type SimpleMod and click OK
9. Write an initial no-op implementation:

package org.lorinhochstein.simplemod;

import net.minecraftforge.fml.common.Mod;
import net.minecraftforge.fml.common.event.FMLInitializationEvent;

@Mod(modid = SimpleMod.MODID, version = SimpleMod.VERSION)
public class SimpleMod {
    public static final String MODID = "simplemod";
    public static final String VERSION = "1.0";

    @Mod.EventHandler
    public void init(FMLInitializationEvent event)
    {
        // nothing here yet
    }
}

Delete ExampleMod.java

Delete src/main/java/com/example/examplemod/ExampleMod.java. Easiest is to click on it in IDEA and hit the "delete" key.