Public API

These are the runtime services a Java addon calls into once it has a data definition in hand. They read the same registries the datapack does, so an addon and a datapack resolve the same way.

API	Purpose
MxtDatapackRegistries	Queries native datapack registries, holders, disabled tags and client-synchronised data.
AuraService	Queries the final aura at a position, its environment sources, the aura pools separated by resource and area overrides; a resource may carry element markers.
ResourceService	Initialises, reads and modifies resources, and performs maximum and regeneration calculations.
CultivationService	Cultivation, resource conversion, realm breakthrough and realm assignment.
AbilityService	Server-side ability execution, costs, cooldowns, cancellation and actions.
FriendService / FriendEvent	Decides whether one entity treats another as its own. FriendEvent.Relation answers with the vanilla TriState, so another mod can give its own verdict; the judge is named by a UUID plus an optional entity, so a source that keeps its data in a server manager (a team, a faction) can still answer while the player is offline. DEFAULT hands the question to the built-in friend system, which posts no further event; when the judge is offline that system reads FriendCache, the in-memory mirror both ends of the session refresh.
FormationActionType / MxtFormationActionTypes	A formation's functional modules: formation.actions selects one with type, and each module's own fields live on its own record. Adding one is a record plus one DeferredRegister registration; the runtime dispatches on the record type, so the data package never touches the world.
FormationProtection	Queries whether an action is stopped by a formation's protection module: it applies when either the actor or the target is inside the radius. When delegate_to_claims is set and claim protection is currently in force (FtbChunksCompat.claimsProtect(), constrained by the server option formation.delegate_requires_claims), the whole decision is handed to the claim plugin, so it then always answers "not prevented". It takes the actor's UUID rather than a ServerPlayer, so another mod that hooks its own event can reuse the same judgement, including the owner's unconditional exemption and the friend exemption controlled by config.
CurrencyValueService	Computes an item's currency value and handles the reason it is unavailable.
ItemMatcher	The item matching syntax of a data definition: ItemMatcher.Entry has five kinds — item, tag, wildcard, regex and spirit_storage — and supports the single-entry shorthand (an item id or a tag) next to mixed arrays; find/findAll take the first/all of them in ascending priority.
NumberProvider	Constants, expressions, registry type dispatch and finite value handling.
DefinitionText	Turns a datapack definition into a name: with a Holder or a ResourceKey in hand, call name(holder) directly, and the category defaults to the registry's own path (mxt:fire in mxt:aura looks up aura.mxt.fire). The few that are not translated under the registry path are declared once in its internal CATEGORIES (such as mxt:item_quality → quality), so one definition can never have two names in a tooltip and in the item picker.

warning

Unless an interface is explicitly marked as a client API, do not call server lifecycle registry queries from the render thread.