How to fix Minecraft crashing on launch (Fabric 1.21.1)

If Minecraft 1.21.1 closes right after you press Play, work through this list in order. Most Fabric crashes come from a mismatched mod, the wrong Java version or a missing dependency.

1. Check your Java version#

Minecraft 1.21.1 needs Java 21. Open Command Prompt and type java -version. If it shows an older version, follow the Java 21 guide.

2. Remove the last mod you added#

Move the newest mod out of your mods folder and launch again. If the game starts, that mod was the cause. Look for a newer file that supports 1.21.1.

3. Check every mod's version and loader#

Each mod must list Minecraft 1.21.1 and Fabric. Files for Forge, NeoForge, Quilt or a different Minecraft version will not load. The Modrinth mods guide shows how to filter for the right file.

4. Make sure Fabric API is installed#

Many mods need Fabric API. If a crash report says a dependency is missing, install the version that matches 1.21.1.

5. Test with no mods#

Launch a clean 1.21.1 Fabric profile with only Fabric API. If that works, add mods back one at a time.

6. Review your memory setting#

Too little memory can crash heavy mod setups, and a huge value can also cause trouble on low-RAM PCs. Around 4 GB is a safe starting point for most Fabric setups. See the RAM guide.

7. Update your graphics driver#

Crashes on startup that mention graphics or OpenGL are often fixed by updating your GPU driver from the manufacturer.

8. Read the crash report#

Minecraft writes a crash report when it fails. In the standard setup it is saved in the crash-reports folder inside your game folder. Look near the top for the mod name and for lines starting with "Caused by".

Ask for help the safe way#

Share only the relevant part of the report in the FireClient Discord. Never post account files, access tokens or unredacted logs that contain personal paths.