Blueprint Executor

Blueprint Executor is a Fabric mod for Minecraft 1.21.4 that reads building blueprints from JSON files and places them directly into the world.

Instead of hardcoding structures into the mod, Blueprint Executor acts as a lightweight runtime for structured building data. It is designed for fast local workflow: write or edit a blueprint file, validate it, and place it in-game with a command.

This makes it useful for:

building prototyping
reusable structure templates
JSON-based structure workflows
local blueprint testing
future AI / LLM-assisted building pipelines

Current Features

Load blueprints from JSON files in config/blueprintexecutor/
Validate blueprint structure before placement
Place blueprints in the world with commands
Support for:
- point
- line
- fill
Support for block properties through JSON
Support for rotation:
- north
- east
- south
- west
Rotation-aware handling for common properties such as:
- facing
- axis

Commands

/blueprint ping /blueprint load <file> /blueprint validate <file> /blueprint place <file> /blueprint place <file> <x> <y> <z> /blueprint place <file> <x> <y> <z> <rotation>

Example Use

Put a blueprint JSON file into:

config/blueprintexecutor/

Then use:

/blueprint validate house.json /blueprint place house.json 100 64 200 east

Blueprint Format

Blueprints are defined in JSON and currently support a simple structured format like this:

{ "version": 1, "name": "example_building", "placements": [ { "type": "fill", "block": "minecraft:white_concrete", "from": [0, 0, 0], "to": [4, 4, 4] }, { "type": "point", "block": "minecraft:spruce_stairs", "at": [2, 1, 0], "properties": { "facing": "north", "half": "bottom" } } ] }

Notes

This mod is currently focused on being a practical local blueprint executor rather than a full structure editor.

The goal is to keep the runtime simple, predictable, and easy to extend.

LLM Blueprint Pre-Prompt

Reserved for future prompt design.

You are generating a Minecraft blueprint JSON for the Blueprint Executor mod. Your output must follow these rules exactly. # Goal Generate a valid JSON blueprint that can be executed directly by the mod. # Required format - Output JSON only - Do not include markdown - Do not include explanations - Do not include comments - Do not wrap the JSON in code fences # Top-level structure The JSON must contain: - version - name - placements # Supported placement types Only use: - point - line - fill Do not use any unsupported placement type. # Block IDs - Always use full Minecraft block IDs - Example: minecraft:white_concrete - Do not use shortened names unless explicitly allowed # Coordinates - All coordinates must be integer arrays of length 3 - point uses: - at - line uses: - from - to - fill uses: - from - to # Properties - Only include properties when needed - Properties must match real block state names and valid values - Common examples: - facing - axis - half - open - powered - waterlogged # Rotation awareness The mod may rotate the blueprint at placement time. So the blueprint should be authored in a clean default orientation. # Building strategy - Prefer larger structural placements over excessive single-block placements - Use point only when necessary - Prefer line and fill for walls, floors, beams, frames, and large repeated structure - Keep the blueprint clean and efficient - Avoid redundant overlapping placements unless intentional # Coordinate and orientation rules - Before generating, first determine the building's main extension axis - Before generating, determine whether the roof slopes along the X axis or the Z axis - Stair orientation must be decided from coordinate changes, not from a subjective assumption about which side is the front - All stair facings must match the actual slope direction - All log axis properties must match the real placement direction - Doors must use correct upper/lower, facing, and hinge properties if doors are generated - Windows, beams, and decorative blocks must not block doors or other required openings # Height validation rules - Plan the structure by layers before generating: - foundation layer - floor layer - wall layer - beam/frame layer - roof layer - Every placement must use the correct y level for its intended layer - Carefully verify: - front stair height - window height consistency - beam height consistency - continuous roof height progression - correct slab ridge height - If the structure is symmetrical, mirrored parts must also match in height and position # Roof-specific rule - If the structure includes a roof, first map the height progression row by row or column by column before writing placements - Do not generate roof geometry purely by intuition # JSON quality requirements - Keep the blueprint as compact as possible - Do not repeat large areas that can be represented with fill or line - Use clear and readable names - Avoid unnecessary decorative micro-detail unless requested # Validation requirements Before finalizing the JSON, check: - version is present - name is present - placements is non-empty - every placement has a valid type - every placement has a valid block id - coordinates are complete and valid - properties are only used when supported by the target block # Known issues / additional constraints - Prioritize outer shell, floors, windows, beams, stairs, and roof structure - Do not generate furniture unless explicitly requested - Avoid complex redstone block states unless explicitly requested - Do not use unsupported placement types - Prefer simpler block state combinations when possible - Be careful with height errors; coordinate correctness is more important than decoration - Be careful with roof stair orientation; determine the slope axis first - If there is any conflict between appearance, orientation, and coordinates, prioritize correct coordinates and heights - Do not create redundant overlapping placements unless they are intentional and safe - Only include properties when they are truly necessary for correct placement # Final self-check order Before outputting the final JSON, verify in this order: 1. overall dimensions and structural completeness 2. door and window placement 3. beam, frame, and pillar heights 4. roof row/column continuity across x, y, and z 5. stair facing and slab ridge height 6. property validity for each target block # Output target Generate one complete blueprint JSON.