View and test Minecraft jigsaw structures without launching the game

Every jigsaw block, drawn where it actually points

Blockwright reads the jigsaw connectors out of a structure’s block-entity NBT — name, target, pool, final_state and joint — and draws each one in the scene as an anchor cube with an arrow cone pointing along its front face. Colours are assigned per pool and stay stable, so two connectors that belong together look like they belong together.

There is an x-ray pass as well, so a connector buried inside the build is still visible from outside, and hovering a row in the panel puts a focus shell around that marker in 3D. After an assembly runs, markers are built for every placed piece, not just the one you opened.

Template pools, resolved instead of assumed

The pool inspector lists every distinct pool your connectors point at and tells you what is actually behind the name: whether the pool file exists, how many elements it resolves and which ones are missing, what its fallback is, and whether that fallback resolves either. The colour chips match the arrows in the scene, so a broken pool is a colour you can go and look at.

It re-reads whenever the Worldgen Studio saves, which makes the authoring loop edit → save → re-simulate → look at it in 3D, with the game closed the whole time.

Simulate the assembly across seeds

One seed proves nothing: a jigsaw structure that assembles beautifully on the seed you tested is exactly how a pool with one bad weight ships. Simulate seeds plans a batch of random seeds in one go and keeps every plan, so you can click through the runs and see the spread — how far the assembly expanded, which pieces got picked, where it terminated.

Clicking a run re-shows it from the piece cache rather than replanning it, and the seed field follows your selection so a re-roll continues from the run you were looking at. The panel lists the placed pieces of the assembly, and clicking a piece opens that piece’s own file.

The failures Minecraft never reports

When a jigsaw structure generates wrong in-game, the game does not explain itself: you get a village with a hole in it, or nothing at all. The assembler here emits the rejections by name instead.

• overlap

  A slot stayed empty because every aligned candidate partially crossed bounds already placed — vanilla’s "boxes may only touch or be contained" rule, which is the usual reason a piece is simply absent.

• unsupported-orientation

  Pieces with a matching target name exist, but none of them can face that connector: Y-only rotation cannot fix a vertical/horizontal axis mismatch.

• fallback-expansion

  A fallback pool contains pieces that themselves expand — the standard way an assembly blows straight past the size declared on the structure def.

• waterlog risk & mob equipment

  An aquatic-biome def with a waterloggable start pool (vanilla force-waterlogs below the surface), and saved mob gear that natural generation will re-roll.

Structure Lint: the per-file checks

Alongside the assembly, a linter reads the file itself and reports what will bite later: explicit air on the boundary of a dense capture (which clears the terrain it is pasted into), blocks the target Minecraft version does not know — with the curated same-shape stand-in named — orphaned palette entries, and data markers with empty metadata.

Every finding carries a position, so clicking a row focuses that exact cell in the 3D scene. The Workspace Check-Up runs the same rules across the whole data pack.

Worldgen Studio: the four files that decide whether it spawns

The structure def, the template pool, the structure set and the biome tag are the four JSONs standing between a finished build and a structure that appears in a world. The Worldgen Studio puts validated forms over all of them: terrain adaptation, size, max distance from center, biomes, spacing and separation, start-pool element weights and fallback.

Writes are surgical. Each file is re-read and only the modelled fields are patched, so spawn_overrides, processors, salt and empty elements survive byte-for-byte — hand-authored worldgen is not rewritten by an editor that only understood part of it. Validation gates the save on the things that fail silently in-game: an empty biome list, separation greater than or equal to spacing, a size outside 1–7, and a max_distance_from_center over 116 when terrain adaptation is on (vanilla adds 12 and rejects anything over 128).

Workspace Check-Up: the audit before you launch the game

The Worldgen Doctor scans an entire data pack for the failures that produce no error message at all — a jigsaw structure def with no spawn_overrides (the codec requires the field even as an empty object, or the pack refuses to load), an empty biome tag, a dead pool reference, an .nbt past the Structure Block limit, a structure folder using the pre-1.21 name. The safe ones have Fix it buttons.

Watch mode keeps the viewer and the project panel in sync while external tools — a datapack build, an Axiom export, VS Code — edit the same files underneath you.