Add an Ability

An ability is the unit of gameplay a player spends aura on. It carries its own costs, cooldown, condition, target selection and behaviour, which means a single JSON file can describe a bolt, a buff, a passive bonus or a reaction to being hit.

This tutorial adds two abilities to the example pack: an active bolt cast from the hotbar, and a triggered recovery that answers damage.

What You Are Building

File	Purpose
data/example/mxt/ability/qi_bolt.json	An active ability with a cost, a cooldown and an area target.
data/example/mxt/ability/qi_recovery.json	A triggered ability that reacts to being hurt.
data/example/mxt/realm_stage/foundation.json	(edited) grants the bolt on breakthrough.
data/example/mxt/item_binding/root_pellet.json	(edited) also grants the recovery ability.
data/example/mxt/technique/azure_breath.json	(edited) grants both once learned.

Step 1 — An Active Ability

// data/example/mxt/ability/qi_bolt.json
{
  "ability": {"type": "mxt:active", "slot": "primary"},
  "icon": "example:textures/gui/ability/qi_bolt.png",
  "costs": [
    {"type": "mxt:resource", "resource": "example:qi", "amount": 10}
  ],
  "cast_time": 10,
  "cooldown": 40,
  "condition": {"type": "mxt:has_realm", "aura": "example:qi"},
  "target_selector": {"type": "mxt:area", "radius": 6, "include_actor": false},
  "bi_entity_action": {
    "type": "mxt:target_action",
    "action": {"type": "mxt:damage", "amount": "6 + caster_level * 0.5"}
  }
}

Field	What it does
ability.type	Selects the lifecycle from the built-in ability_type registry: empty, active, triggered, modifier, aura, channelled, composite, word. mxt:active is the type that appears on the ability hotbar.
ability.slot	The hotbar slot group, primary by default, and it must not be blank.
icon	Optional. A bare string is a 16x16 GUI texture; an object is an item stack template ({"id": ...}, optionally count and components). Without it the entry is drawn with its name.
costs	A list of Cost objects, paid before the behaviour runs. mxt:resource consumes a resource, mxt:item consumes items, and the {"id": ..., "amount": ...} shorthand means mxt:resource.
cast_time	Cast duration in ticks; the hotbar draws a casting progress bar while it runs.
cooldown	Cooldown in ticks, reported back to the client so the hotbar can grey the slot.
condition	An entity condition that must pass before the ability can be used. Its only job here is to keep Mortals from throwing bolts. For a passive mxt:modifier or mxt:aura ability the same field keeps working after the cast: it is re-checked every tick and the passive effect is withdrawn while it fails.
target_selector	Which entities the bi-entity behaviour applies to. mxt:self (the default) selects only the caster; mxt:area selects everything within radius (capped at 128), and include_actor decides whether the caster is part of that set.
bi_entity_action	Run for each selected target, and a failing one never stops the rest. mxt:target_action forwards an entity action to the target — here 6 damage plus half the caster's experience level.
entity_action	Runs on the caster. It defaults to mxt:no_op; use it for a self-buff, a particle burst or an aura change.

Two extra fields are worth knowing about:

• components adds state instead of a plain number: mxt:charges, mxt:cooldown, mxt:toggle, mxt:timer, mxt:resource and mxt:target_lock. Each of them declares a storage slot, and the values live in the ability attachment that owns the grant, addressed by the ability's id; see Data Storage Types for which of them anything actually reads yet.
• element_affinity lists elements (or element tags) the ability belongs to. When it is not empty, the formula variable element_modifier becomes available and can scale damage or costs by how well the caster's spirit root matches.

Where realm ranks come from

An ability formula runs in an entity context. It provides caster_health, caster_max_health, caster_level (the vanilla experience level), caster_<resource> and caster_<attribute> — but not realm_rank, which only exists in formulas evaluated for one resource. Use caster_example_qi when an ability should scale with the caster's aura.

Step 2 — A Triggered Ability

A triggered ability fires when the world does something to its owner. The trigger also injects a few variables that describe what happened.

// data/example/mxt/ability/qi_recovery.json
{
  "ability": {
    "type": "mxt:triggered",
    "triggers": [{"type": "mxt:hurt"}],
    "chance": 1
  },
  "cooldown": 100,
  "condition": {"type": "mxt:has_realm", "aura": "example:qi"},
  "costs": [
    {"type": "mxt:resource", "resource": "example:qi", "amount": 5}
  ],
  "entity_action": {"type": "mxt:heal", "amount": "2 + damage * 0.5"}
}

• triggers is a list of built-in matchers: tick, attack, hurt, kill, block_break, block_use, item_use, equip, death, breakthrough and technique_stage. None of them takes a field of its own.
• chance is a number provider, 1 by default, and it is rolled per matching trigger.
• The hurt trigger adds damage — the damage actually inflicted — which is why the heal can scale with the hit. The other triggers add their own names: target_health and target_is_living for attack, block_x/y/z for block events, use_duration for item_use, and so on.

The full variable table is in Formula Variables.

Step 3 — Granting the Abilities

Defining an ability does nothing on its own: an entity has to hold it. The mxt:grant_ability entity action does that, and its source field records who granted it.

From a realm. Edit the realm the player reaches:

// data/example/mxt/realm_stage/foundation.json
"success_action": {
  "type": "mxt:grant_ability",
  "ability": "example:qi_bolt",
  "source": "example:foundation"
}

success_action runs on the stage the player just entered, so reaching Foundation Establishment teaches the bolt. ability_requirements on a stage is the mirror image: it lists abilities that must already be held before the breakthrough is allowed.

From an item. Add the action to any binding table:

// data/example/mxt/item_binding/root_pellet.json
"actions": [
  {"type": "mxt:grant_spirit_root", "spirit_root": "example:fire_root"},
  {"type": "mxt:grant_ability", "ability": "example:qi_recovery", "source": "example:root_pellet"}
]

From a spirit root, physique or technique. Those definitions have a granted_abilities list that is applied while they are held:

// data/example/mxt/technique/azure_breath.json
"granted_abilities": ["example:qi_bolt", "example:qi_recovery"]

Source identities

Keep source stable and meaningful — the definition ID that granted the ability is a good choice. Abilities from different sources are tracked separately, and a source is what makes a later removal traceable, so two items can grant the same ability without one of them silently revoking the other.

Step 4 — Using the Ability Hotbar

Active abilities appear on the shared client hotbar:

1. /mxt ability opens the Configure Hotbar screen for the ability entries. A slot you deliberately leave empty stays empty, and a saved entry whose ability no longer exists is refilled from the current runtime list.
2. Hold the ability keybind (LAlt by default, "Show Ability Hotbar") and press a number key 1–9 to cast the entry in that slot. Several keys can be held at once, and the client setting "Open Mode" switches between "Hold to Show" and "Press to Toggle".
3. Everything is server-authoritative: the client only sends a use or cancel request, and the server decides costs, cooldowns, durations and effects. Cancelling a channelled ability works the same way.

Step 5 — Verify

Abilities are a data pack registry, so load the world again rather than running /reload:

(load the world again)
/mxt registries validate              → no codec errors
/mxt attachment status                → lists the abilities the entity holds
/mxt ability cast example:qi_bolt     → forces the cast (gamemaster permission)

1. Before entering the chain, /mxt ability cast example:qi_bolt fails: the condition rejects it.
2. Break through to Foundation Establishment and check /mxt attachment status. The bolt is now held, and source shows it came from the realm.
3. Open the hotbar with LAlt and cast it. 10 qi is deducted, the cooldown starts, and nearby entities take damage. Compare the value shown by /mxt resource example:qi before and after.
4. Set the pool too low with /mxt resource example:qi set 5 and cast again: the cast is refused because the costs cannot be paid, and nothing is deducted.
5. Take a hit with qi_recovery granted: the heal amount scales with the damage taken, 5 qi is spent, and the 100-tick cooldown prevents it from firing again immediately.

Common Mistakes

Symptom	Cause
The ability never appears on the hotbar	Only mxt:active abilities are listed; a triggered, modifier or channelled ability has no hotbar entry of its own.
A channelled ability cannot be released from the hotbar	mxt:active and mxt:channelled are mutually exclusive types. Wrap the channelled ability as the child of an mxt:composite ability and make the composite the top-level definition.
Costs are never paid	ResourceCost uses resource, but an ability's costs is a list of Cost. Write {"type": "mxt:resource", "resource": ..., "amount": ...} or the {"id": ..., "amount": ...} shorthand — not {"resource": ...} without a type.
An ability formula is always 0	It used a variable its context does not provide, such as realm_rank in an entity formula. The name is reported at evaluation time: a development environment logs the whole error, production logs one warning line per distinct message, and both continue with 0.
mxt:word does nothing	It is a terminal, code-whitelisted effect (self_heal, purge_self_curses) and requires an operator by default. It is not a way to run commands.
Everyone has the ability immediately	It was granted by a granted_abilities list on a spirit root, physique or technique that everybody satisfies — those lists apply while the definition is held.

Next

• Ability — the full field list, including components and channelled upkeep.
• Action Types and Condition Types — everything an ability can do and check.
• Loot and Advancement Criteria — rewards and advancements that react to breakthroughs and ability use.