Check Engine

Check Engine

Know what's wrong with your modpack, in plain English. Check Engine checks your pack every time the game starts and tells you about broken, missing and duplicate mods. In a world, one command checks every recipe, loot table and quest for items from mods you don't have.

Made for pack makers, server owners and anyone who's ever stared at "Mod loading has failed" wondering which of 400 mods is the problem.

---

How to use it

Put the Check Engine jar in your mods folder and launch. That's it. No config, no gameplay changes.

Startup popup

Every time the game starts, Check Engine checks the whole pack. If something's wrong, you get a clear screen before the title screen (saved to checkengine/boot-report.txt). If everything's fine, you'll never see it.

It finds:

• Duplicate mods: two versions of the same mod, and which one actually loads
• Missing dependencies: a mod needs another mod you don't have
• Hidden missing mods: a mod uses another mod's code without listing it, so the loader can't warn you
• Wrong versions: a mod needs a different Minecraft, NeoForge, Forge or library version
• Incompatible mods: mods that say they don't work together
• Wrong loader: Fabric or Forge mods dropped into a NeoForge pack, and the other way round
• Broken downloads: half-finished jars and .zip files in the wrong folder
• Client-only mods on a server
• Memory: how much RAM the pack needs, and whether it's getting enough

Every finding says what's wrong, which file it is, and how to fix it.

/checkengine scan

Run it in a world (needs op/cheats) to check every recipe, loot table and FTB Quests file for items from mods that aren't installed: the stuff that silently breaks after you remove a mod. The report goes to checkengine/scan-report.txt.

/checkengine startup

Shows how long the last startup took and which mods were slowest. The full report goes to checkengine/startup-report.txt.

"Why can't I join?"

When a server kicks you for mismatched mods, you get a clear list of what's missing and which versions don't match, instead of a wall of text.

---

Want to check a pack before launching?

There's also a free standalone checker, Check Pack.bat, on GitHub. Drag a modpack folder onto it and it runs the same check without starting the game, so it even works on packs that won't start at all. It can also explain your last crash report, build a server pack and compare your pack with a server.

---

Versions

Minecraft	Loader
26.1.2	NeoForge
1.21.1	NeoForge
1.20.1	Forge

FAQ

Does it change anything in my pack?
No. It only reads files and writes its reports to a checkengine folder.

Does it need to be on the server too?
No, it works on client, server or both. On a server it checks the pack at startup and adds the scan command.

Can I put it in my modpack?
Yes, please do. It's MIT licensed. Your players get a clear message instead of a confusing crash.

It flagged something that works fine.
Please tell us (see Feedback below). We test against real packs (ATM10, FTB Skies 2, Techopolis 3, Better MC and more), and every false alarm gets fixed.

---

Feedback welcome!

Check Engine is brand new, and the best way to make it better is real packs. Please tell us:

• It flagged something that works fine (a false alarm)
• It missed a problem that crashed your game
• Ideas for things it should check

Leave a comment below, or open an issue on GitHub, with your report from the checkengine folder (boot-report.txt or scan-report.txt). Long reports: upload them to mclo.gs and paste the link. Every report helps, and false alarms get fixed first.

Check Engine is open source: github.com/Uanme37/CheckEngine