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Common Errors

When something goes wrong, Carbon shows you a message like this:

[Carbon] Error in src/definitions/items.cj line 6:
  "durabilty" is not recognised. Did you mean "durability"?

This page lists the most common errors and how to fix them.

Missing carbonjava Header

Error:

[Carbon] Error in src/definitions/items.cj line 1:
  File does not start with "carbonjava". This file will not be loaded.

Fix: Make sure the very first line of your file is exactly:

carbonjava

No spaces before it, no capital letters, nothing else on that line.

Typo in a Property Name

Error:

[Carbon] Error in src/definitions/items.cj line 8:
  "durabilty" is not recognised. Did you mean "durability"?

Fix: Check the spelling. Carbon will usually suggest the correct word. Look it up in the relevant reference file if you're unsure.

Missing end

Error:

[Carbon] Error in src/definitions/items.cj line 14:
  Reached end of file but "add item" block was never closed. Did you forget "end"?

Fix: Every add block needs a matching end. Count your add and end keywords — they should be equal.

add item          ← opens block
name (ruby)
type ingredient
end               ← closes block. Required!

Wrong File in run

Error:

[Carbon] Error in src/definitions/items.cj line 10:
  Could not find "scripts/firbal.cj". Check the file name and path.

Fix: Check that the file exists and that the path and spelling are correct. Paths start from inside src/.

run (scripts/fireball.cj)     ← correct
run (scripts/firbal.cj)       ← typo
run (fireball.cj)             ← missing folder name

Wrong Classloader Target (Allotrope Only)

Error:

[Carbon] Error loading allotrope mod "my_mod":
  "src/guifix.cj" targets "#FabricMainWindow.java" which is a child-only class,
  but this file is listed under "parent" mixins. Move it to "child" in carbon.mod.json.

Fix: Check your carbon.mod.json. Make sure files targeting Minecraft classes are in "child" and files targeting the Carbon Loader window are in "parent".

Invalid Value for a Property

Error:

[Carbon] Error in src/definitions/items.cj line 7:
  "tier" expects wood, stone, iron, diamond, or netherite. Got "ruby".

Fix: Use one of the accepted values. Check the reference file for the full list of valid values for each property.

Missing Required Property

Error:

[Carbon] Error in src/definitions/items.cj:
  "add item" block is missing required property "type".

Fix: Make sure you include all required properties. For items, name and type are always required.

Nested add Without end

Error:

[Carbon] Error in src/definitions/mobs.cj line 18:
  Found "add behaviour" but the previous "add drops" block was never closed.

Fix: When you nest blocks (like add drops inside add mob), each inner block needs its own end before the outer block's end.

add mob
  name (ruby_slime)

  add drops
    drop (ruby, 0.5, 1, 3)
  end              ← closes add drops

end                ← closes add mob

Script Input Mismatch

Error:

[Carbon] Error in src/scripts/wave_spawner.cj line 3:
  This script expects input "mob_type" but it was called without any arguments.

Fix: When calling a script that declares input (...), you must pass the arguments in run:

run (scripts/wave_spawner.cj, mob_type)    ← correct
run (scripts/wave_spawner.cj)              ← missing argument

Invalid carbon.mod.json

Error:

[Carbon] Could not load mod: carbon.mod.json is missing required field "id".

Fix: Open carbon.mod.json and check all required fields are present: id, name, version, authors, minecraft_version, type

Using run for a Minecraft Command

Error:

[Carbon] Error in src/scripts/example.cj line 4:
  "run" is for .cj scripts only. To run a Minecraft command, use "cmd" instead.
  Example: cmd (/msg target "hello")

Fix: Replace run (/msg ...) with cmd (/msg ...).

Quick Checklist When Something Doesn't Work

  1. Does every .cj file start with carbonjava?
  2. Does every add have a matching end?
  3. Are all file paths spelled correctly?
  4. Are all property names spelled correctly?
  5. Is carbon.mod.json valid and complete?
  6. Are all required properties included (name, type, etc.)?