Adding an Attribute

If your skill should buff something vanilla has no attribute for — like the built-in Swim Speed, Lure Speed and Fishing Luck skills — register a new attribute. Experience Skills will keep the skill's level modifier on it in sync for you, but you must still add it to the player's AttributeSupplier and implement what it does.

1. Register the Attribute

Register during your plugin's registration phase, before the registries freeze:

RegistryHandler<Attribute, Attribute> myAttribute =
    ExperienceSkillsAPI.registerAttribute(
        "mymod",
        "harvest_yield",
        new RangedAttribute("attribute.name.harvest_yield", 0.0, 0.0, 1024)
            .setSyncable(true)     // sync to the client if the effect is client-visible
    );

registerAttribute returns a handle; use myAttribute.holder() when registering the skill.

Match the built-ins

Experience Skills' own custom attributes (swim_speed, lure_speed, fishing_luck) are RangedAttributes created exactly like this. A RangedAttribute is almost always what you want.

2. Buff It From a Skill

Pass the attribute's holder as the skill's attribute:

registry.register(
    "harvesting",
    new SkillsConfig(true, 0.5f, 100, 5, 0xC0FF33,
        AttributeModifier.Operation.ADD_VALUE, 100,
        ModStats.BLOCK_BROKEN.id()),
    myAttribute.holder()          // ← the custom attribute
);

From here Experience Skills keeps a level-scaled modifier on the attribute in sync automatically.

3. Add It to the Player

Experience Skills only manages the modifier. For the attribute to exist on the player at all, you must add it to the player's AttributeSupplier, the same as any modded attribute. On each loader that means hooking the "entity attribute creation / modification" event and adding your attribute to the player type.

TIP

If the attribute is registered using ExperienceSkillsAPI.registerAttribute() it will add to player and living entity automatically.

4. Implement the Effect

Registering an attribute and putting a modifier on it does nothing on its own — an attribute is just a number. You have to read that number somewhere and apply it. For example, a "harvest yield" attribute might be read in a block-drop hook to roll for bonus drops, or a movement attribute might be read each tick to adjust the player's velocity. This is the same work any mod does for its own attributes.

Checklist

1. Register the attribute during your plugin phase.
2. Buff it from a skill via handle.holder().
3. Add it to the player's AttributeSupplier.
4. Implement whatever reads the attribute and applies the effect.
5. Add a lang entry for its display name (the translation key you passed to the attribute), e.g. "attribute.name.harvest_yield": "Harvest Yield".

Modifier only

Experience Skills syncs a modifier on the attribute — it does not add the attribute to entities or implement its behaviour. Skip steps 3 or 4 and your skill will level up and hold a modifier on an attribute that either doesn't exist on the player or does nothing.