Duplicate Mod
Loading fails because the same mod is present twice. Two copies, often different versions of one mod, sit in the mods folder, and the loader refuses to choose between them.
What does this error mean?
Each mod id may load only once. 'Found duplicate mod' means two jars declare the same mod id, so the loader cannot decide which to use and stops. Usually you simply left an old version behind when updating.
Found duplicate mod
Most Common Causes
- An old version of a mod left in place after updating.
- The same mod downloaded twice under different filenames.
- A mod bundled inside another and also installed separately.
- Copying mods between folders without cleaning up.
- A library included by two mods and also added manually.
How To Diagnose
- Read the log for the duplicated mod id and the two file paths.
- Open the mods folder and find both jars.
- Compare versions to keep the correct one.
- Check for bundled copies inside larger mods.
Recommended Fixes
- Delete the old copy
Remove the outdated/duplicate jar, keep only the version you want. - Clean the mods folder
Audit for any other duplicates after big updates. - Avoid manual library copies
Do not add a library that another mod already bundles. - Rebuild the folder if unsure
Start from a clean mods folder and add each mod once.
Frequently Asked Questions
Mod ids must be unique per load. Two jars with the same id create an unsolvable conflict.
Normally the newer version for your Minecraft/loader, delete the other.
Look closely, the filenames or versions differ. The log lists both exact paths.