Installing mods on Minecraft 1.21.4 with Fabric takes four steps and about five minutes. The process is the same on Windows, macOS, and Linux — only the folder paths differ.

This guide covers everything from a clean install, including where to download mods safely and how to fix the most common errors.

What you need before starting

  • Minecraft Java Edition — already installed and launched at least once on 1.21.4
  • Java 21 — required by Minecraft 1.21+. The official Minecraft launcher bundles its own Java, but external tools need a system Java. Download from Adoptium if you need it separately.
  • 5–10 minutes

You do not need to own or install OptiFine. You do not need CurseForge's app if you prefer manual installation. Both are optional.

Step 1 — Install the Fabric loader

The Fabric loader is the modding framework. It goes between Minecraft and your mods.

  1. Go to fabricmc.net and download the installer for your OS
  2. Open the installer
  3. Select Minecraft Version: 1.21.4 from the dropdown
  4. Leave Loader Version on the latest stable
  5. Leave Install Location as the default (your .minecraft folder)
  6. Click Install

The installer adds a new profile to your Minecraft launcher automatically. You will see it named something like "fabric-loader-0.16.x-1.21.4" in the Installations tab.

Do not change the Loader Version unless a specific mod requires an older one. Always use the latest stable Fabric loader for 1.21.4.

Step 2 — Find your mods folder

Mods are .jar files placed in a specific folder. The location depends on your OS:

OS Path
Windows %AppData%\.minecraft\mods
macOS ~/Library/Application Support/minecraft/mods
Linux ~/.minecraft/mods

Windows shortcut: Press Win + R, type %AppData%\.minecraft\mods, press Enter. The folder opens directly.

If the mods folder does not exist, create it. It must be named exactly mods inside your .minecraft directory.

If you use multiple Minecraft instances (different versions, different mod sets), each instance has its own .minecraft folder. Make sure you're putting mods in the right one. Launchers like Prism Launcher or MultiMC manage separate instances automatically.

Step 3 — Install Fabric API

Fabric API is required by almost every Fabric mod. It is a mod itself — a set of common utilities that mod authors use so they don't have to rebuild basic game hooks themselves.

Download it from Modrinth: modrinth.com/mod/fabric-api

  • Click Versions
  • Filter by 1.21.4
  • Download the latest release (.jar file)
  • Place it in your mods folder

Do not rename the file. Do not unzip it. .jar files go into the mods folder as-is.

Step 4 — Download and install your mods

Where to download mods safely:

  • Modrinth (modrinth.com) — the recommended source. Mods are verified, fast CDN, no adware wrappers.
  • CurseForge (curseforge.com) — the original repository, still widely used, safe if you use the direct download links.

Avoid random .jar downloads from YouTube descriptions, unofficial "mod packs" on third-party sites, or mirror sites. Malicious mods exist and they target Minecraft players specifically.

For each mod you want:

  1. Go to Modrinth, search for the mod name
  2. Click Versions, filter by 1.21.4 and Fabric
  3. Download the .jar file
  4. Place it in your mods folder

Example — installing Sodium:

  1. Search Modrinth for "Sodium"
  2. Versions → 1.21.4 → Fabric → download sodium-fabric-0.6.7+mc1.21.4.jar
  3. Drop it into .minecraft/mods/

Repeat for each mod. A typical performance setup (sodium, lithium, fabric-api) is three files in the mods folder.

Step 5 — Launch and verify

  1. Open the Minecraft launcher
  2. Select the Fabric profile (the one the installer created)
  3. Click Play

On the main menu title screen you should see something like "Fabric Loader 0.16.x, Fabric API x.x.x" in the lower-left corner. If you see the Fabric version listed, your mods are loading.

Press F3 in-game and look at the top of the debug screen — the mod count appears next to the Fabric loader version.

Common errors and fixes

"Incompatible mods" crash on launch

A mod is not compatible with your Minecraft version or Fabric loader version. The crash log (in .minecraft/crash-reports/) names the conflicting mod. Fix: download the correct version of that mod for 1.21.4.

"Could not find or load main class" / game doesn't start

Fabric loader installed into the wrong .minecraft folder. Verify the Fabric profile in the launcher points to the same folder where your mods are.

Game launches but mods don't appear

You placed the .jar files in the wrong folder, or you launched the vanilla profile instead of the Fabric profile. Check both.

"Requires Fabric API" error

You're missing Fabric API or have the wrong version for 1.21.4. Download it from Modrinth and place it in the mods folder.

Two mods conflict (crash with both installed)

Some mods are incompatible with each other. Common conflicts in 1.21.4:

  • Indium + Sodium 0.6+ — do not install Indium with Sodium 0.6 or higher, it's built in
  • OptiFine + anything — OptiFine doesn't run on Fabric; use Iris instead
  • Two versions of the same mod — ensure you have exactly one .jar per mod

Using Modrinth App (optional shortcut)

Modrinth App is a launcher that manages mod installations for you — dependency resolution, version matching, update notifications. If you're managing more than 10 mods, it saves time.

The app creates its own instance folder separate from the vanilla launcher. Mods installed through the app don't appear in your main .minecraft/mods/ folder — they live in the app's instance directory.

Keeping mods updated

Mods update frequently, especially after Minecraft point releases. When Mojang releases 1.21.5, most mods will need updated versions.

The safest approach: before updating Minecraft, check that your mods have 1.21.x-compatible releases on Modrinth. Update Minecraft version only after your key mods are ready.

Download links: