Define a Curse

A curse is a lasting state carried by an entity. The definition decides how long it lasts, how often it fires, how it stacks and what behaviour runs at each stage. What may remove it is not decided here — that sentence lives on the antidote side, in a tag.

This tutorial adds one curse to the example pack: example:qi_backlash, a backlash of qi. It expires on a timer, fires every 100 ticks, stacks up to three times, and refreshes its remaining time whenever it stacks.

What You Are Building

File	Purpose
data/example/mxt/curse/qi_backlash.json	A curse that expires on a timer: stacks, periodic behaviour, and what happens on apply and on expiry.

Step 1 — Types and Fields

A curse definition lives in data/<namespace>/mxt/curse/<path>.json. type is the only required field, and it decides only how this definition lives out its life and on what beat it runs behaviour; the four types are on Curse Types, and this page uses the timed mxt:timed.

Step 2 — The Definition and Its Fields

{
  "type": "mxt:timed",
  "duration_ticks": 600,
  "tick_interval": 100,
  "max_stacks": 3,
  "stacking_mode": "add_stacks_refresh_duration",
  "on_apply": {"type": "mxt:apply_effect", "effect": "minecraft:weakness", "duration_ticks": 200},
  "on_tick": {"type": "mxt:apply_effect", "effect": "minecraft:hunger", "duration_ticks": 100}
}

Field	Type	Default	Effect
type	Curse type	required	One of the four above.
duration_ticks	Number or formula string	0	How long it lasts, in ticks.
tick_interval	Number or formula string	20	Interval of the periodic behaviour; only a finite value greater than 0 drives on_tick on a period.
max_stacks	Integer	1	Stack ceiling, 1..256.
stacking_mode	Enum	ignore	What happens while it is already held, see the next step.
application_condition	Entity condition	mxt:always	Whether it may be applied; failing it makes the application fail.
display_condition	Entity condition	mxt:always	Whether the character information panel lists this row.
on_apply	Entity action	mxt:no_op	Runs once when an instance is created.
on_tick	Entity action	mxt:no_op	The periodic behaviour.
on_expire	Entity action	mxt:no_op	Runs on natural expiry.
on_cleanse	Entity action	mxt:no_op	Runs when it is cleansed.

Each behaviour field takes a single action or an array of them. on_apply runs only when an instance is created: stacking onto, or refreshing, one already held does not run it again.

Only two moments in a curse's own life run behaviour — natural expiry runs on_expire, being cleansed runs on_cleanse. Outside decisions such as an explicit removal or a replace displacing the old instance run neither.

Step 3 — Stacking

stacking_mode decides what a second application does while that curse is already held:

Value	While it is already held
ignore	Nothing at all: the stacks stay, the remaining time stays, on_apply does not run again, and nothing is reported.
refresh_duration	The stacks stay and the remaining time is refreshed by this request.
add_stacks_refresh_duration	The stacks become min(max_stacks, current + requested) and the remaining time is refreshed.
add_stacks_keep_duration	The stacks become the same min, but the original remaining time stays.
replace	The old instance is removed as "replaced" and runs none of its behaviour; then the new instance goes through, on_apply included.

The default is ignore: leave stacking_mode alone and a second application does nothing, so the stack count stays at whatever the first one set. The example writes add_stacks_refresh_duration, so applying it three times climbs to three stacks.

Two different curses can coexist: the framework has no exclusion rule. To get exclusion, write it into application_condition yourself — a "carries no other curse" condition (mxt:not around mxt:has_curse).

Step 4 — Applying and Conditions

Entry point	Effect
Entity action mxt:apply_curse	Applies one curse; it takes stacks and duration_ticks.
Entity action mxt:apply_curses	A list of entries, each applied on its own.
Vanilla loot function mxt:apply_curse	Applies a curse, with the source recorded as loot.
An item's mxt:curse_container	Applies on equipping, across all six equipment slots and the Curios slots. While that curse is already held it only registers this item's source and does not apply it again — neither the stacks nor the remaining time move.
Command /curse apply	See the command table in the next step.

Places that name one specific definition (mxt:apply_curse, mxt:remove_curse, an item's mxt:curse_container) take a concrete id only. mxt:remove_curses_by_tag and vanilla tag filtering take a # tag, whose file lives in data/<namespace>/tags/mxt/curse/<path>.json. A definition has no "who may remove me" field: list the curse under an mxt:curse tag and the cleansing side recognizes it.

application_condition decides whether an application is allowed at all, and display_condition decides whether the character information panel shows the row; both default to mxt:always. Elsewhere, these read or write curses: the entity condition mxt:has_curse (all four filters optional), the item condition mxt:curse_container, and the loot condition mxt:has_curse (one extra entity field, choosing which entity in the loot context to ask about).

Step 5 — Removal and Commands

Entry point	Result
Natural expiry	A mxt:timed duration runs out and on_expire runs.
Entity action mxt:remove_curse	Removes one named curse under the cleansing reason, so on_cleanse runs.
Entity action mxt:remove_curses_by_tag	Removes every held curse carrying any one of the given tags, each running its own on_cleanse.
/curse cleanse <target> <tag>	The command side of cleansing; the tag is a bare id (example:cleanse/poison), without the #.
/curse remove <target> <curse>	Removes the whole instance and wipes every source at once, under the explicit reason, so no definition behaviour runs.
An item's mxt:curse_container being cleansed	Once the component stops carrying that curse, this item's own source is released; the instance only leaves once the last source is gone.
purge_self_curses on the mxt:word ability type	Clears the caster's own curses, also under the explicit reason, so on_cleanse does not run.

Every removal posts an event, cancellable at the Pre stage by default; the one where replace displaces the old instance only posts an after-the-fact notice.

There is no "irremovable" switch. The two things closest to it: mxt:empty runs nothing at all, and when a definition is not in the current data pack (the file is gone, or a neoforge:conditions block keeps it out) an instance already held is frozen — no periodic behaviour, no natural expiry, cleansing refused, and an explicit removal the only way off.

Command	Effect
/curse list [target]	Lists names, stacks, ticks left or "never expires", and every source. Without a target it looks at you, and it needs no permission.
/curse apply <target> <curse> [stacks] [duration]	Needs administrator permission; stacks is 1..256, and the duration can only tighten what the definition declares.
/curse remove <target> <curse>	Needs administrator permission.
/curse cleanse <target> <tag>	Needs administrator permission, and the argument is a bare id without #.

The top-level alias /curse is switched by Server Config → Command Aliases → /curse; /mxt curse stays complete when it is off.

Verify

/mxt registries validate
/curse list
/curse apply @s example:qi_backlash 2
/curse list

1. Data packs are read when the world loads, not on /reload; after editing the file, back out to the title screen and reopen the world (or restart the server).
2. /mxt registries validate passing means the definition made it into the registry.
3. /curse apply @s example:qi_backlash 2 puts two stacks on you, and /curse list shows the name, the stacks, the ticks left and every source.
4. Apply one more stack: add_stacks_refresh_duration climbs it to three and refreshes the remaining time. Applying again still leaves three — max_stacks caps it.
5. 600 ticks later it expires on its own; /curse remove @s example:qi_backlash ends it right away.
6. display_condition decides whether the character information panel lists the row.
7. The test pack ships curse probes (granted by /mxt_test kit and then fired by hand) — use one on yourself to watch applying, stacking and cleansing.

Common Mistakes

Symptom	Cause
The world will not load, pointing at an mxt:timed duration	The constant duration_ticks is not greater than 0. Loading stops it.
The world will not load, pointing at an empty triggers	An mxt:triggered curse needs at least one trigger. Loading stops it.
The definition never makes it into the registry	max_stacks is outside 1..256, so decoding fails.
Nothing was applied and the log says nothing	duration_ticks evaluated to something non-finite or negative, so that application is void; a mxt:timed formula that evaluates to 0 or less does the same, because loading can only judge constants.
An action stays silent while the command says the application failed	application_condition did not hold: the action side never reads the result back, so it says nothing; the command reports the failure.
mxt:apply_curse does nothing at all	The stack count evaluated outside 1..256, which is skipped silently and leaves nothing in the log.
Applying a second time had no effect	stacking_mode defaults to ignore: while the curse is held it does nothing and reports nothing.
/curse cleanse says it cannot be done	The definition is not in the current pack, so the instance is frozen and only an explicit removal is left.
Two curses that should exclude each other both landed	The framework has no exclusion rule; write it into application_condition yourself.
A second piece of gear carrying the same curse did not raise the stacks	While it is already held, equipping only registers that item's source and does not apply it again.

Next

• curse — the complete field table, the source ledger, the three moments of mxt:curse_container and the display rules.
• Curse Types — the fields and duration rules of each lifecycle.
• /curse — every subcommand.
• Entity Action Types — the fields of mxt:apply_curse, mxt:apply_curses, mxt:remove_curse, mxt:remove_curses_by_tag and mxt:apply_effect.
• Entity Condition Types — the filters of mxt:has_curse.
• Loot and Criteria — curses in loot conditions and loot functions.
• Ability Types — purge_self_curses on mxt:word.