Coming from Minecraft modding

RSMM was deliberately shaped around the Minecraft modding mental model. If you have written a Forge, Fabric, or NeoForge mod, most of what you know transfers — only the words and the file formats change.

The one big difference

Minecraft mods ship code that runs inside a modded game. RSMM mods ship data that RSMM bakes into the game’s own cooked-asset files — no modded runtime required for most content. Scripted behaviour is the exception, via the optional loader DLL. See Mods ship data, not code.

Rosetta table

Minecraft modding	RSMM equivalent	Notes
fabric.mod.json / mods.toml	manifest.toml	Mod metadata + declared content.
Registries / DeferredRegister	Content kinds (Mod.item, Mod.enemy, …)	Register a definition cloned from a vanilla base.
Tags (#minecraft:logs)	Tags (Mod.tag)	Cross-mod, append-only named groups.
Mappings (Yarn / MCP / Mojmap / SRG)	Symbol map (data/symbols.json)	Semantic names → engine functions/globals.
Access Transformers / Access Wideners	callable symbols (engine::Name())	Exposes raw engine functions as typed calls.
Mixins (SpongePowered)	Loader DLL hooks + event bus (R.on)	Runtime behaviour injection (MinHook + Lua).
Data generation (datagen)	SDK emitters (engine/*_cook)	RSMM materializes cooked bytes at apply time.
Data packs	Declarative [[content]] / [[patch]]	No code; merged by the applier.
Resource packs	Texture/asset overrides	Work without the loader DLL.
Lang files (en_us.json)	i18n (lang/<locale>.toml)	Merged into the game’s text banks.
Mod loader (Fabric Loader / Forge)	RSMM + winhttp.dll loader	Asset mods need only RSMM; Lua needs the loader.
Game-version compat (1.20.1)	target_game_build + pattern resolver	Byte-pattern resolution survives game updates.
Inter-mod APIs (@ApiStatus, IMC)	R.api.expose / R.api.require	Version-gated published APIs.
Dependencies (depends/recommends/suggests/breaks)	requires / recommends / suggests / conflicts	Semver ranges + load-order, cycle & conflict checks before apply.

How the analogies hold up

Registries → content kinds

In Forge you register a new Item into a registry. In RSMM you clone a vanilla base and register a new definition:

import rsmm.sdk as sdk
m = sdk.Mod(id="RubyMod", name="Ruby Mod")
dagger = m.item("RubyDagger", base="Knife", name="Ruby Dagger")
m.commit()

Like a registry, each kind validates and de-dupes ids. Unlike Minecraft, each kind carries a confidence (confirmed / experimental / guess) because the byte format is reverse-engineered — see Content kinds.

Mappings → the symbol map

Minecraft’s obfuscated names are made readable by a mappings file. RSMM’s engine functions read as FUN_140xxxxxxx in a fresh disassembly; data/symbols.json is the canonical map to semantic names, and — like a refmap — it resolves by byte pattern, not fixed address, so names survive game patches. See Mappings.

Mixins → loader hooks

Where you would write a Mixin, RSMM detours the function natively in the loader DLL or subscribes to a generated event from Lua (R.on("<event>", cb)). Both are opt-in and only load when the loader is present.

Dependencies → manifest deps + load order

fabric.mod.json’s depends / recommends / suggests / breaks map one-to-one onto manifest fields, with the same hard/soft severities and the same npm-style semver ranges (>=1.2 <2.0, 1.2.x, ^1.2, ~1.2, *):

[mod]
id = "RubyExpansion"
version = "1.3.0"
requires   = ["RubyCore >=1.2 <2.0"]   # depends:    hard — apply refuses if unmet
recommends = ["BetterLoot ^1.0"]        # recommends: warn only
suggests   = ["SoundPack"]              # suggests:   info only
conflicts  = ["OldRubyMod"]             # breaks:     hard — refuse if both enabled
replaces   = ["RubyMod"]                # auto-disables the older mod
load_order = 90                          # lower loads earlier (default 100)

Before the applier touches the game, RSMM builds the dependency graph: it errors on a missing/out-of-range requires, a hard conflicts, a requires cycle, or a duplicate id; warns on a missing recommends; and computes a deterministic load order (load_order, then priority). Run rsmm doctor to see the report. This is the loader’s “won’t launch with unsatisfied dependencies” check, done ahead of time.

Where to go next

• Your first mod — the Minecraft “make a block” equivalent.
• Authoring mods — the full how-to.
• Concepts — the understanding-oriented pages.