Hello, I have this lines in my build.gradle, but when I build the mod and start Minecraft with the mod in Modrinth it says 

Quote

java.lang.NoClassDefFoundError: org/java_websocket/server/WebSocketServer

Can anyone help me with this problem?

jarJar.enable()

dependencies {
    minecraft "net.minecraftforge:forge:${minecraft_version}-${forge_version}"
    annotationProcessor("org.spongepowered:mixin:0.8.5-SNAPSHOT:processor")

    // Forge"s hack fix
    implementation("net.sf.jopt-simple:jopt-simple:5.0.4") { version { strictly "5.0.4" } }

    // WebSocket
    minecraftLibrary "org.java-websocket:Java-WebSocket:1.5.3"
    jarJar(implementation("org.java-websocket:Java-WebSocket:1.5.3"))
}

 

Change

 

// WebSocket minecraftLibrary "org.java-websocket:Java-WebSocket:1.5.3"

jarJar(implementation("org.java-websocket:Java-WebSocket:1.5.3"))

 

to

 

// WebSocket
jarJar("org.java-websocket:Java-WebSocket:1.5.3")

 

 

 

 

 

Thanks for your answer, but sadly it still doesn't work. Without minecraftLibrary I can't even build the mod and with it I still get the same error.

Hm I have no idea

 

Try replacing implementation with minecraftLibrary. Dependencies in the minecraftLibrary configuration are added to your compile and runtime classpaths in ForgeGradle 6.

On 9/18/2025 at 1:32 PM, Jonathing said:

Try replacing implementation with minecraftLibrary. Dependencies in the minecraftLibrary configuration are added to your compile and runtime classpaths in ForgeGradle 6.

It still doesn't work

minecraftLibrary is required for dev time for it to load.

jarJar should be enough for runtime.

be sure you're running the latest forge. And make sure you post your debug log.