Invalid mod file / 'is missing mods.toml'
Every mod jar must contain a metadata file (mods.toml for Forge/NeoForge, fabric.mod.json for Fabric). When the error says a jar is missing mods.toml or is an invalid mod file, the jar is not a mod at all: the download was interrupted, the file is 0 bytes, or a zip archive was renamed to .jar without containing a mod.
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How to fix it
- 1
Find the named file
The error names the jar. Open the Files tab → mods/ and locate it. If the log names only a folder path, sort mods/ by size — a 0-byte jar stands out.
- 2
Check the file size
A real mod jar is rarely under 10 KB. A 0-byte or few-hundred-byte file means the download or upload failed partway. Delete it.
- 3
Redownload from CurseForge or Modrinth
Fetch the exact version the pack manifest expects and re-upload it. A renamed zip will fail the same way again — the metadata file must come from the actual mod file.
- 4
Check for double-extracted archives
Sometimes a mod zip was extracted, then the inner folder re-zipped by hand. Download the original jar file directly instead of repacking anything.
- 5
Restart and confirm
Boot once after replacing the jar. If a different jar is now named, repeat — a broken download link in a pack updater can corrupt several files in one run.
Alternative causes
These can produce the same error message — worth ruling out if the steps above don't resolve it.
FTP upload in text mode
ASCII-mode FTP mangles binary jars. Re-upload in binary mode, or use the panel's file manager which always uploads binary-safe.
Antivirus or sync tool truncating files
On self-hosted Windows servers, OneDrive/Dropbox sync and aggressive antivirus can truncate jars mid-write. Exclude the server directory.
Frequently asked
Why would a mod jar have no mods.toml?
Because it was never a mod. A zip renamed to .jar has no metadata. Real mods always ship mods.toml (Forge/NeoForge) or fabric.mod.json (Fabric).
Can I fix it by re-zipping with the metadata added?
No. Hand-repacking almost always produces another invalid jar. Redownload the original file from the mod's official page.
How do I verify a jar downloaded correctly?
Compare file size with the listing on CurseForge/Modrinth, or check the SHA hash the project page publishes. Panel file managers show the size directly.
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Last reviewed 2026-09-06. If a step is wrong or out of date, tell us — we'll fix the article and the auto-pattern at the same time.