SimCity Expansion

Building expansion-pack manager for New-Simukraft-1.21.1

Bring vanilla, Litematica, and WorldEdit structures into the game, convert and install them as buildable SimuKraft buildings, edit them in a Litematica-style manager, and share them as one-click zip packs.

Overview
Features
Requirements and installation
Opening the manager
The manager
Structure editor
Capturing builds from the world
Build packs
Structure formats
Directory layout
Commands
Documentation
Building from source
License
Acknowledgements

Overview

SimCity Expansion is a NeoForge mod for Minecraft 1.21.1 that adds a complete building expansion-pack pipeline to New-Simukraft-1.21.1 (a city-building mod). It lets you import structures from three common formats, convert them into SimuKraft's buildable format, organise and edit them through a Litematica-style manager, and package them as portable zip packs for one-click install and sharing.

Integration with SimuKraft is a pure file-system convention — the mod writes .sk and .nbt files under <game dir>/simukraftbuilding/<category>/ — so there is no compile-time dependency on SimuKraft. The manager is built on Minecraft's own GUI toolkit and needs no extra library, and the command interface runs on a dedicated server as well.

Features

Three structure formats — vanilla .nbt, Litematica .litematic (multi-region auto-merge), and Sponge/WorldEdit .schem (v1/v2/v3), all converted to SimuKraft's vanilla buildable format on install.
Robust conversion — older structures are upgraded through the game DataFixer, missing mod blocks are detected against the registry, and block-entity contents (chest inventories, signs, and so on) are preserved (entities are not).
Litematica-style manager (open with \) — file tree, fixed-width info panel, material list, and layered previews: embedded thumbnail, real-block 3D scene, isometric voxel view, and top-down map.
Full structure editor — place / break / pick / replace, brush painting, box selection with fill / frame / hollow / expand, copy / cut / paste, rotate and mirror, symmetry axis, undo / redo, slice planes, and preset camera views; export to .litematic or save and install directly.
Capture from the world — mark two corners in-game, capture the selection as a blueprint, and optionally include block-entity contents.
Zip pack ecosystem — manifest-tracked install / uninstall, one-click export of installed buildings into a shareable pack, an optional pack icon and an index.json file manifest, and pass-through of SimuKraft native job/trade definitions (format v2).
No hard dependencies — the manager runs on Minecraft's own GUI toolkit and SimuKraft is integrated purely through the file system, so neither is a compile-time dependency.
Server-friendly — the /buildpack command (operator level 2, with tab-completion) installs loose files and packs and captures regions on dedicated servers, reusing the same conversion pipeline as the GUI.
Localised — English, Simplified Chinese, and Traditional Chinese; numbers, dates, and file sizes are formatted per the active game language.

Requirements and installation

Requirement	Version
Minecraft	1.21.1
NeoForge	21.1.233 or newer

Place the jar in your mods/ folder — there are no other mod dependencies. The in-game manager works out of the box on a client; on a dedicated server the jar loads headless and exposes the /buildpack command.

Opening the manager

Press <kbd>\</kbd> (backslash) in-game. All bindings are rebindable under the mod's category in Options -> Controls.

Action	Default key
Open the build pack manager	<kbd>\</kbd>
Set world selection corner A	<kbd>[</kbd>
Set world selection corner B	<kbd>]</kbd>
Capture the selection as a blueprint	<kbd>'</kbd>
Toggle "include block-entity contents"	unbound
Clear the world selection	unbound

The manager

The left panel has three tabs:

Import Files — loose .nbt / .litematic / .schem files in the import directory.
Packs — zip build packs in the import directory, shown as an expandable tree (pack -> category -> building). Any building can be previewed and read directly from the zip, without extracting it first.
Installed — buildings already present in SimuKraft's building directory.

The info panel on the right shows metadata rows, a preview, a material list (counted by block type, with missing blocks flagged), and a .sk metadata form (editable on the Import tab, read-only elsewhere). It supports drag-and-drop import, search, sort, batch install, and two-click delete. When you browse a pack that ships an icon, the icon is shown in the preview area.

Structure editor

Open a structure in the editor to refine it before installing:

Edit — place, break, pick, and replace blocks; paintbrush with adjustable size and paint strokes; remove or replace a whole block type at once.
Selection — box-select a region (click two cells or drag a box face), then fill / frame / hollow / expand / clear it, with copy, cut, and paste.
Transform — rotate 90 degrees and mirror along any axis, with a symmetry axis for mirrored editing.
History — undo and redo.
View — cycle slice planes, fit and focus the selection, preset camera angles, grid and gizmo toggles, and perspective toggle.
Output — Save as New, Save and Install, or Export .litematic.

Press <kbd>H</kbd> inside the editor for the full shortcut list.

Capturing builds from the world

Build something in your world, then turn it into a blueprint without leaving the game:

Look at a block and press <kbd>[</kbd> to set corner A, then <kbd>]</kbd> to set corner B. The selection box is drawn in the world.
Press <kbd>'</kbd> to capture the selection and export it to the import directory.
Optionally bind the "include block-entity contents" key to capture chest inventories and similar data, and the "clear selection" key to reset the corners.

The same operation is available on servers via /buildpack capture (see Commands).

Build packs

Buildings are grouped into five fixed categories: residential, commercial, industry, public, and other.

Install / uninstall — installing a pack converts every building into the matching category directory and records a manifest in simcity_expansion/installed_packs.json, so uninstalling removes exactly the files that pack added.
Export (Installed tab -> Export) — packages the listed buildings (respecting the current search filter) into a zip. Options:
- include .sk metadata,
- include SimuKraft job/trade JSON,
- include an icon — tick the box and leave the path blank to auto-render one from the first building's preview, or supply a custom PNG path.
An index.json file manifest (each packed file with its type, category, size, and SHA-256) is always written at the zip root.
Manifest — pack.json (format 2) carries id, name, version, author, description, an optional icon, and a generated timestamp.

The full pack specification (directory layout, pack.json, .sk / .meta.json metadata, native job/trade JSON, icon.png, and index.json) is documented in docs/pack-format.zh.md.

Structure formats

Extension	Source	Conversion on install
`.nbt`	Vanilla structure block template	Installed as-is; old versions auto-upgraded
`.litematic`	Litematica projection	Multi-region merge into one bounding box; reads embedded name / author / creation time / thumbnail
`.schem`	Sponge / WorldEdit schematic	v1, v2, and v3 supported

All formats are converted to vanilla .nbt on install (SimuKraft's build system only reads the vanilla format). During conversion the structure is DataFixer-upgraded to the current game version, block-entity positions are remapped and preserved, the palette is checked against the registry for missing blocks, and the merged volume is capped at 16,000,000 blocks.

Directory layout

<game dir>/
├── simcity_expansion/
│   ├── import/                 import directory (drop loose files and zip packs here)
│   ├── export/                 exported build packs
│   └── installed_packs.json    installed-pack registry
└── simukraftbuilding/<category>/   SimuKraft building directory (install target)

Commands

All /buildpack subcommands require operator level 2 (game masters) and offer tab-completion.

Command	Description
`/buildpack list`	List the files in the import directory
`/buildpack packs`	List installed packs
`/buildpack install <file> [category] [name]`	Install a loose structure file
`/buildpack installpack <zip>`	Install a whole zip pack
`/buildpack uninstallpack <id>`	Uninstall a pack by its id
`/buildpack activate <zip>`	Serve a pack to SimuKraft virtually (no install) — requires SimuKraft
`/buildpack deactivate <id>`	Stop serving an activated pack
`/buildpack active`	List currently active packs
`/buildpack capture <from> <to> [name] [format]`	Capture a region into a blueprint

Documentation

Document	Audience
Usage guide	Players: import, install, manage, export
Pack format spec v2	Pack authors: layout, `pack.json`, metadata, conversion

Chinese versions are also available: usage.zh.md and pack-format.zh.md.

Building from source

The project uses the Gradle wrapper and a NeoForge ModDevGradle toolchain (JDK 21).

./gradlew build

The built jar is written to build/libs/.

License

All Rights Reserved. Copyright © 2026 xinian. This source is published for reference; it is not licensed for redistribution or derivative works without permission. When using in a modpack, you must link back to the original link.

Acknowledgements

New-Simukraft-1.21.1 — the city-building mod this expands.
devins-badges — the badge artwork in this readme.

About the old version

1.20.1 Forge has been abandoned for development