Fix “requires Fabric API” and other missing mod dependency crashes
What “Incompatible mods found”, “requires fabric-api” and “Missing or unsupported mandatory dependencies” mean, and how to fix each one before the game crashes.
By Elchi, maker of Alloy. Updated . 5 min read.
A “missing dependency” crash means a mod needs another mod (often a library like Fabric API, Architectury or Cloth Config) that isn't installed, or is installed in the wrong version. The fix is to install that mod in a version made for the same Minecraft version and the same loader. The game's error message names exactly which mod and which version.
What the error looks like
Fabric and Quilt
Fabric shows an “Incompatible mods found!” window before the game opens, and the log lists lines like:
Mod 'Architectury' (architectury) 13.0.8 requires version 0.100.0 or later of fabric-api, which is missing!
The part after requires is what to install: here, Fabric API 0.100.0 or newer.
Forge and NeoForge
Forge and NeoForge stop on the loading screen with “Missing or unsupported mandatory dependencies”, followed by a block per problem:
Mod ID: 'architectury', Requested by: 'rei', Expected range: '[13.0.6,)', Actual version: '[MISSING]'
Mod ID is what's missing, Requested by is the mod that needs it, and Expected range is the version it accepts. [13.0.6,) means 13.0.6 or newer. If Actual version shows a number instead of [MISSING], the mod is installed but in a version outside that range.
How to fix it
- Find the mod by its ID on Modrinth or CurseForge. IDs are usually the name in lowercase (
fabric-apiis Fabric API,cloth-configis Cloth Config). - Pick the file for your Minecraft version and loader. A Fabric build of a library won't satisfy a Forge mod, and a 1.20.1 build won't load on 1.21.1.
- Put it in the instance's
modsfolder, next to the mod that needs it. - Check the version range. If the error says a newer version is needed, update the library; if an older one, the mod that asks for it is probably outdated, so update that mod instead.
Other crashes that look like this
A mod made for another loader
Fabric mods don't load on Forge or NeoForge, and the reverse. Many mods publish a separate file per loader; get the right one. On Forge and NeoForge, Sinytra Connector can run many Fabric mods, with its own Forgified Fabric API.
A mod made for another Minecraft version
Most mods only declare support for the version they were built for. Install the file built for your version, even if an older one seems to work.
The wrong Java version
Minecraft 1.16.5 and older run on Java 8, 1.17 on Java 16, 1.18 to 1.20.4 on Java 17, 1.20.5 to 1.21.x on Java 21, and Minecraft 26.1 and newer on Java 25. A mod compiled for a newer Java crashes with UnsupportedClassVersionError.
Two copies of the same mod
Two versions of one mod in the mods folder (often an old one left behind after an update) stop Fabric and Forge alike. Keep the newer one.
How Alloy prevents this
When you press Play, Alloy reads each mod's own metadata: fabric.mod.json, quilt.mod.json, mods.toml and neoforge.mods.toml, including mods bundled inside other jars, plus the dependency lists on Modrinth and CurseForge. It checks every rule above in about a millisecond and shows the problems before Minecraft starts, each with a fix: install the missing mod in the right version, keep the newer duplicate, or switch the loader version. New Fabric instances get Fabric API automatically, since nearly every Fabric mod needs it.
Alloy does this for you. It checks every mod before Minecraft starts and offers a fix for each problem. It's free for Windows and Linux. Download Alloy