LevelZ Inventory Weight Add-on

LevelZ Inventory Weight is an add-on that integrates MT Inventory Weight with LevelZ.

You can download the add-on from Modrinth:

• LevelZ Inventory Weight on Modrinth

It allows the player's LevelZ overall character level and/or a configured LevelZ skill to increase the player's maximum inventory weight capacity.

This add-on is not standalone. It requires both LevelZ and MT Inventory Weight.

1.21 and 1.20.1 behave differently

This page covers both the 1.21 and the 1.20.1 builds. They share the same idea but the underlying LevelZ API is very different, so several features exist only on 1.21.

Feature	1.21	1.20.1
Overall-level scaling	Yes	Yes
Skill-level scaling	Yes	Yes
Custom carrying skill	Yes	No
Uses one of the 12 built-in LevelZ skills	Yes*	Yes
Dynamic skill creation (dynamicSkill.*)	Yes	No
LEVELZ_ATTRIBUTE capacity mode	Yes	No
skill.capacityMode option	Yes	No
skill.showInLevelZScreen / GUI hiding	Yes	No
skill.skillIdOverride	Yes	No
Datapack skill JSON (data/levelz/skill/…)	Yes	No

* On 1.21 you can use any skill key, including the custom carrying skill or a built-in one.

On 1.20.1, LevelZ skills are a fixed enum with no registration API. That means there is no carrying skill, no dynamic creation, no attribute mode, and no GUI hiding. The 1.20.1 build instead reads one of the 12 existing built-in skills (config skill.skillKey, default strength) plus the overall level. Sections that are 1.21-only are clearly marked below.

Required Dependencies

You must install:

• LevelZ
• MT Inventory Weight
• Fabric API
• Fabric Language Kotlin
• fzzy_config

What This Add-on Does

LevelZ Inventory Weight can increase max inventory weight from:

1. The player's total LevelZ character level. (1.21 and 1.20.1)
2. One configured LevelZ skill. (1.21 and 1.20.1)
3. A dynamically created LevelZ skill, if enabled and missing. (1.21 only)
4. A LevelZ skill attribute using inventoryweight:generic.max_weight, if LEVELZ_ATTRIBUTE mode is selected. (1.21 only)

On 1.21, the recommended setup is to use a custom LevelZ skill called:

carrying

This skill can be shown in the LevelZ skill screen or hidden through the add-on config.

1.20.1: no custom skill — use a built-in one

There is no carrying skill on 1.20.1, and you cannot create one. Pick one of the fixed built-in skills via skill.skillKey instead (default strength).

Valid skill.skillKey values on 1.20.1 (case-insensitive):

health, strength, agility, defense, stamina, luck,
archery, trade, smithing, mining, farming, alchemy

Thematic suggestions: strength (default, fits "carry more"), stamina (endurance), or defense (tanky builds). On 1.21 you may also use any of these built-in keys instead of carrying.

Capacity Formula

When using the recommended EVENT_MODIFIER mode (1.21) — or the only mode on 1.20.1 — the add-on modifies max weight with this formula:

final max weight = (current max weight + additive bonuses) * multiplier bonuses

The current max weight is the value already calculated by MT Inventory Weight before this add-on changes it.

This means the add-on can stack with:

• MT Inventory Weight server config max weight
• armor pockets
• other Inventory Weight add-ons
• attribute bonuses
• future capacity providers

Example

Base max weight: 100
Overall LevelZ level: 10
Skill level (carrying on 1.21, e.g. strength on 1.20.1): 10

Overall multiplier per level: 0.01
Skill multiplier per level: 0.05

Overall multiplier: 1 + 10 * 0.01 = 1.10
Skill multiplier:   1 + 10 * 0.05 = 1.50

Final max weight: 100 * 1.10 * 1.50 = 165

Configuration File

The add-on uses a synced server config through fzzy_config.

The config id is:

levelz_inventoryweight:server-config

The config is registered as a synced server/client config, so server gameplay settings can be synchronized to clients.

INFO

Config values are server-authoritative. In multiplayer, the server decides how much capacity LevelZ levels and skills give.

Main Config Options

General

Option	Default	Description
enabled	true	Master switch for the integration.
minimumMaxWeight	1.0	Safety minimum for the final max weight.

Overall Level Formula

The overallLevel section controls how the player's total LevelZ character level affects max inventory weight.

Option	Default	Description
overallLevel.enabled	true	Enables overall-level scaling.
overallLevel.additivePerLevel	0.0	Flat max-weight bonus per total LevelZ level.
overallLevel.multiplierPerLevel	0.01	Multiplier bonus per total LevelZ level. 0.01 means +1% per level.

Example:

overallLevel.multiplierPerLevel = 0.01
overall level = 20
multiplier = 1.20

Skill Formula

The skill section controls how one configured LevelZ skill affects max inventory weight.

Option	Default	Description	Version
skill.enabled	true	Enables skill-based scaling.	both
skill.skillKey	carrying (1.21) / strength (1.20.1)	LevelZ skill key to use.	both
skill.additivePerLevel	0.0	Flat max-weight bonus per configured skill level.	both
skill.multiplierPerLevel	0.05	Multiplier bonus per configured skill level. 0.05 = +5%/level.	both
skill.showInLevelZScreen	true	Shows or hides the configured skill in the LevelZ screen.	1.21 only
skill.capacityMode	EVENT_MODIFIER	Determines how the skill affects capacity.	1.21 only
skill.skillIdOverride	-1	Optional numeric skill id override. -1 resolves by skill key.	1.21 only

TIP

Use skillKey instead of hardcoding the skill id when possible. LevelZ skills can be changed by datapacks, so resolving by key is safer.

1.20.1: smaller config

On 1.20.1 the keys skill.capacityMode, skill.showInLevelZScreen, and skill.skillIdOverride do not exist, and the entire dynamicSkill section is gone. If you copy a 1.21 config, those keys are simply ignored on 1.20.1. Also set skill.skillKey to a built-in skill — carrying resolves to nothing on 1.20.1 and contributes level 0.

Capacity Modes

1.21 only

Capacity modes are a 1.21 feature. 1.20.1 has only the event-modifier behavior and no capacityMode option to choose — LevelZ 1.20.1 has no skill-attribute system, so the inventoryweight:generic.max_weight attribute cannot be attached to a LevelZ skill.

EVENT_MODIFIER

EVENT_MODIFIER is the recommended mode (and matches what 1.20.1 always does).

In this mode, LevelZ Inventory Weight reads the configured LevelZ skill level and modifies MT Inventory Weight's max capacity through the MT Inventory Weight event system.

This mode supports:

• flat bonuses
• multiplier bonuses
• overall level scaling
• skill level scaling

Example:

skill.capacityMode = EVENT_MODIFIER
skill.skillKey = carrying
skill.multiplierPerLevel = 0.05

This means:

+5% max inventory weight per Carrying level

At Carrying level 20:

1 + 20 * 0.05 = 2.0

So the configured skill gives a 2x max-weight multiplier.

LEVELZ_ATTRIBUTE

1.21 only

LEVELZ_ATTRIBUTE does not exist on 1.20.1.

LEVELZ_ATTRIBUTE lets the LevelZ skill use the MT Inventory Weight max-weight attribute directly:

inventoryweight:generic.max_weight

This is best for flat attribute bonuses.

Example:

dynamicSkill.attributeValuePerLevel = 10.0
dynamicSkill.attributeOperation = ADD_VALUE

This means:

+10 max inventory weight per skill level

At skill level 20:

+200 max inventory weight

WARNING

For inventoryweight:generic.max_weight, ADD_VALUE is recommended.

ADD_MULTIPLIED_BASE and ADD_MULTIPLIED_TOTAL are usually not useful for this attribute because the Inventory Weight attribute base value is normally 0.

Carrying Skill

1.21 only

The custom carrying skill, its datapack JSON, translations, and icon are a 1.21 feature. On 1.20.1 there is no custom skill and data/levelz/skill/inventory_weight.json is not loaded — use a built-in skill via skill.skillKey instead.

The add-on is designed to work well with a custom LevelZ skill called:

carrying

If you want to define or modify this skill using LevelZ datapacks, add this file:

data/levelz/skill/inventory_weight.json

For mod/project resources, the equivalent development path is:

src/main/resources/data/levelz/skill/inventory_weight.json

If a developer or modpack author needs to modify the Carrying skill, they should create or override this exact file and use this exact base structure:

{
  "carrying": {
    "replace": false,
    "id": 12,
    "key": "carrying",
    "level": 20,
    "attributes": []
  }
}

The default LevelZ skills normally use IDs 0 through 11, so 12 is the normal next id for the custom carrying skill.

WARNING

LevelZ skill IDs should be continuous. If another datapack or mod also adds a skill with id 12, you may need to change the Carrying skill id.

To resolve an id conflict, create/override:

data/levelz/skill/inventory_weight.json

or, inside a mod project:

src/main/resources/data/levelz/skill/inventory_weight.json

Then change the skill id inside that JSON file and also change the matching skill id in the LevelZ Inventory Weight config.

Skill Translation and Icon (1.21 only)

To display the skill name and info in the LevelZ GUI, add translations:

assets/levelz/lang/en_us.json

Example:

{
  "skill.levelz.carrying": "Carrying",
  "skill.levelz.carrying.0": "Increases your maximum inventory weight.",
  "skill.levelz.carrying.1": "This skill is used by LevelZ Inventory Weight.",
  "skill.levelz.carrying.2": "Depending on server config, it can use either formula scaling or the Inventory Weight attribute."
}

LevelZ also expects a 16x16 icon:

assets/levelz/textures/gui/sprites/carrying.png

INFO

If the icon is missing, the LevelZ GUI may show a missing-texture icon for the skill.

Dynamic Skill Creation

1.21 only

Dynamic skill creation does not exist on 1.20.1. LevelZ 1.20.1 has no API to register or modify skills at runtime, so the entire dynamicSkill.* section is absent on that build.

The add-on can dynamically create the configured LevelZ skill if it does not already exist.

This is controlled by:

dynamicSkill.createIfMissing

If enabled, the add-on checks whether LevelZ already has a skill with the configured skill.skillKey. If not, it creates one.

Dynamic skill config options:

Option	Default	Description
dynamicSkill.createIfMissing	true	Creates the configured skill if LevelZ does not already have it.
dynamicSkill.skillId	12	Skill id for the dynamically created skill. -1 uses the next free id.
dynamicSkill.maxLevel	20	Max level of the dynamic skill.
dynamicSkill.attributeDisplayId	-1	Attribute display id for LevelZ's attribute panel. -1 hides it.
dynamicSkill.attributeBaseValue	-10000.0	Base value for LEVELZ_ATTRIBUTE mode. -10000.0 keeps the normal base.
dynamicSkill.attributeValuePerLevel	10.0	Attribute value per skill level in LEVELZ_ATTRIBUTE mode.
dynamicSkill.attributeOperation	ADD_VALUE	Attribute modifier operation in LEVELZ_ATTRIBUTE mode.

WARNING

If you already include data/levelz/skill/inventory_weight.json, then LevelZ loads the carrying skill from the datapack file. In that case, dynamic creation normally does nothing because the skill already exists.

Hiding the Carrying Skill from LevelZ Screen

1.21 only

GUI hiding does not exist on 1.20.1. There is no custom skill to hide, and the 1.20.1 LevelZ screen classes differ (SkillScreen / SkillInfoScreen / SkillListScreen instead of LevelScreen), so the client mixins are not present on that build.

The add-on can hide the configured skill from the LevelZ skill screen using a client-side mixin.

The skill is hidden when:

skill.enabled = false

or when:

skill.showInLevelZScreen = false

This is useful if the skill exists from a datapack file but the server disables the carrying integration.

WARNING

Hiding is safest when the hidden skill is the final skill id.

For the default LevelZ skill list, carrying should normally use id 12, after the default ids 0 through 11.

Do not hide a middle skill id unless you know the LevelZ GUI can handle it.

Datapack Attribute Example

1.21 only

This applies to the 1.21 datapack skill JSON, which 1.20.1 does not load.

If you want the Carrying skill to directly use the Inventory Weight attribute, the LevelZ skill JSON can include:

{
  "carrying": {
    "replace": false,
    "id": 12,
    "key": "carrying",
    "level": 20,
    "attributes": [
      {
        "type": "inventoryweight:generic.max_weight",
        "operation": "ADD_VALUE",
        "value": 10.0
      }
    ]
  }
}

This gives:

+10 max inventory weight per Carrying level

TIP

If you use the attribute directly in LevelZ JSON, avoid also using EVENT_MODIFIER skill scaling for the same skill, otherwise the bonus may be applied twice.

Recommended Setup

On 1.21

For most modpacks, use:

skill.capacityMode = EVENT_MODIFIER
skill.skillKey = carrying
skill.additivePerLevel = 0.0
skill.multiplierPerLevel = 0.05

And keep the Carrying skill JSON with no attributes:

{
  "carrying": {
    "replace": false,
    "id": 12,
    "key": "carrying",
    "level": 20,
    "attributes": []
  }
}

This gives multiplier-based scaling while keeping the LevelZ skill itself simple.

On 1.20.1

There is no custom skill, no capacity mode, and no datapack file. Use a built-in skill:

enabled = true

overallLevel.enabled = true
overallLevel.multiplierPerLevel = 0.01

skill.enabled = true
skill.skillKey = strength
skill.additivePerLevel = 0.0
skill.multiplierPerLevel = 0.05

This gives multiplier-based scaling from the existing Strength skill plus a small overall-level bonus — no extra resources needed.

Multiplayer Support

LevelZ Inventory Weight supports multiplayer.

The server is authoritative for:

• whether the integration is enabled
• overall level formula
• skill formula
• capacity mode (1.21 only)
• dynamic skill creation (1.21 only)
• final max weight calculation

On 1.21, clients use synced config data for GUI-related behavior, such as hiding the configured LevelZ skill from the LevelZ screen. On 1.20.1 there is no client-side GUI behavior to sync (no skill hiding); the client only needs the synced numeric config.

Troubleshooting

The Carrying skill does not appear (1.21)

Check:

• skill.enabled is true
• skill.showInLevelZScreen is true
• the skill exists through datapack JSON or dynamic creation
• the skill id does not conflict with another LevelZ skill
• the LevelZ datapack was loaded successfully

The Carrying skill appears even when disabled (1.21)

If you include:

data/levelz/skill/inventory_weight.json

LevelZ will still load the skill. The add-on uses a client-side mixin to hide it from the LevelZ screen when disabled.

Make sure the add-on mixin file is included in fabric.mod.json.

Attribute mode gives no multiplier effect (1.21)

This is expected in most cases.

inventoryweight:generic.max_weight normally has a base value of 0, so multiplied attribute operations may not produce useful results.

Use:

EVENT_MODIFIER

for multiplier scaling.

Use:

LEVELZ_ATTRIBUTE + ADD_VALUE

for flat per-level bonuses.

Skill level changes but max weight does not change

Check:

• enabled = true
• skill.enabled = true
• skill.skillKey matches the LevelZ skill key (on 1.20.1, a built-in key like strength)
• skill.capacityMode is correct (1.21 only)
• skill.multiplierPerLevel or skill.additivePerLevel is above 0
• MT Inventory Weight is installed and working

Dynamic skill creation does nothing (1.21)

This usually means the skill already exists.

If this file exists:

data/levelz/skill/inventory_weight.json

then LevelZ creates the carrying skill before dynamic creation runs, so the add-on skips dynamic creation.

On 1.20.1, skill.skillKey = carrying does nothing

Expected — carrying does not exist on 1.20.1, so the skill contributes level 0. Set skill.skillKey to one of: health, strength, agility, defense, stamina, luck, archery, trade, smithing, mining, farming, alchemy.

My 1.21 config keys are missing on 1.20.1

Expected. capacityMode, showInLevelZScreen, skillIdOverride, and dynamicSkill.* do not exist on 1.20.1. They are ignored if present and have no effect.

Related Documentation

• MT Inventory Weight
• LevelZ
• fzzy_config