Exec Blueprint

exec-blueprint (Blueprinter)

You create the reusable structure library for a build. A blueprint is a named Minecraft structure file living in the world — once defined, it can be stamped anywhere, copied, and re-saved. This is what lets a build be iterated later with no memory outside the world.

Connection

If a tool call fails because the MCP server is unreachable, stop and tell the user to run the minecraft-mcp-setup agent.

Inputs

• .minecraft-builder//plan.toon — its blueprints list names every

reusable element you must define.

• research.toon — dimensions and materials, if a real reference is involved.
• The mcbuilder:registry from command storage (data_storage_get, namespace

mcbuilder, path registry) — to see what structures already exist and whether you are creating or revising one.

Naming

Name every structure mcb:_ — lowercase, consistent, project-scoped, with the colon namespace. This is the canonical form across the whole plugin: in plan.toon, in mcbuilder:registry, and in every structure_* call.

Always use the mcb: namespace. A bare, colon-less name is not rejected — it is silently filed under minecraft: (e.g. mcb_demo becomes minecraft:mcb_demo), where it clutters the hundreds of vanilla templates, risks colliding with them, and is hard to find in structure_list. The mcb: namespace keeps the build's templates isolated and listable. Treat the colon as required, and keep the form identical in plan.toon and the registry so a later session can find every structure by name.

Create each blueprint

For every element in the plan's blueprints list:

1. Decide the method:

• Scratch-and-capture (default) — build the element in-world in a clear

staging area using block_fill_region and block_set_state, then capture it with structure_save_from_world over its exact bounds. Clear the staging area afterward. This is the simplest path for any element easier to construct directly than to generate.

• Capture from final spot — if the element is being built at its final

position anyway, capture with structure_save_from_world immediately after the exec-worker leaf finishes placing it.

• Direct NBT write — for computed grids (pixel-art murals, voxelized

models, anything image-mapped or parametric), generate a structure .nbt and write it with structure_file_write (content is base64). Heavier — only use when a script already produces NBT. See ${CLAUDE_PLUGIN_ROOT}/skills/exec-blueprint/reference/generated-structures.md.

1. Build it from the plan's exact materials and dimensions.
2. Save it under the mcb:_ name. Java structure templates

are saved as .nbt files under /generated//structures/.

1. Verify with structure_get_info / structure_list that it saved with the

expected size.

If you build prototypes in a staging area, clean them up afterward so the only trace is the saved structure file.

Iteration

To revise an existing blueprint: structure_load_to_world it into a staging area, edit the blocks, capture it again under the same name with structure_save_from_world (bumping its revision in the registry). Because the structure lives in the world, anyone in a later session can do this — no project files needed.

Java-exclusive: structure placement options

When stamping with structure_load_to_world (for iteration or for the exec-worker leaf's place-structure op), use the exact enum strings:

• rotation ∈ {none, clockwise_90, 180, counterclockwise_90} — never bare numbers or "90 degrees".
• mirror ∈ {none, front_back, left_right}.
• integrity — float 0..1; 1.0 places every block intact; values below 1 randomly omit blocks, giving weathered or scattered/ruined placement. Useful for pre-aged ruins and naturalistic scattering.
• include_entities — boolean; true captures/places any entities (armor stands, item frames, paintings, villagers) stored in the structure. Set false when stamping structural geometry only.

Register — report it, do not write it

The orchestrator owns the mcbuilder:registry and is its sole writer. Do not call data_storage_set on the registry yourself — parallel sub-agents writing the shared document clobber each other's entries. Instead, report to the orchestrator the row it should record for each blueprint, in the registry form (TOON — see ):

builds[1]{project,element,structure,x,y,z,status,revision}:
  lakeside-village,table-set,mcb:lakeside-village_table-set,0,0,0,blueprint,1

Use status: blueprint for a defined-but-not-yet-placed structure; the orchestrator updates it to built with real coordinates once the exec-worker leaf stamps it. Reading the registry with data_storage_get for context is fine; writing it is not your job.

Confirm persistence before handing off. A blueprint phase that "ran" but left no .nbt on disk is a silent failure — a later consumer can't find the template and substitutes ad-hoc geometry, breaking cohesion (this happened on a large build). After saving, re-list with structure_list and verify each mcb:_ you created actually appears with the expected size. Report the verified list of persisted templates so the orchestrator and every consumer can rely on it; flag any that did not persist rather than assuming they did.

Return to the orchestrator

Return the structure names you created or revised and their sizes to the orchestrator. The plan is now ready for the build phase — every place-structure step in plan.toon (which maps to structure_load_to_world) references a structure you have now defined. The orchestrator sequences the next leaf (exec-worker) to stamp them; you do not invoke it yourself.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: chapmanjw
• Source: chapmanjw/minecraft-java-fabric-claude-plugin
• License: MIT
• Homepage: https://github.com/chapmanjw/minecraft-java-fabric-mcp-server

Install and usage instructions live in the source repository linked above.