Feature Lab
Feature Lab shows you what a Minecraft Bedrock worldgen feature actually does. Open a
features/ or feature_rules/ JSON file and it renders the blocks that file would place in a 3D
view beside your code — or draws your whole pack as a graph you can read, search and edit.
Two commands, both in the Command Palette from the moment the extension is installed:
| Command |
Needs |
What you get |
| Feature Lab: Open Feature Graph |
The pack folder open |
Every feature in the pack, as connected cards you can edit |
| Feature Lab: Preview Feature |
A feature JSON open in the editor (Ctrl+Alt+P / Cmd+Alt+P) |
The blocks this feature places, in a rotatable 3D panel |
First run
- Open your behaviour pack folder — anything with a
features/ directory in it. Open the
pack folder itself, not the parent that holds both packs. (If you do open the parent, the
graph still finds the pack inside it.)
- Run
Feature Lab: Open Feature Graph from the Command Palette — Ctrl+Shift+P, then type
"Feature Lab". No file needs to be open: the graph is about the pack, not about one file.
- For the 3D preview instead, open a feature JSON and press
Ctrl+Alt+P. A preview is of one
feature, so this one does need a file — or click a card in the graph.
Nothing to install. The engine ships inside the extension.
The feature graph
Every feature and rule in the pack is a card; every places_feature is an edge. Cards are
colour-coded by what the delegation is — a scatter, a weighted pick, a sequence — so the shape
of a pack is visible before you read a line of it.
Select a card and the right-hand panel becomes a form for that feature, built from the type's real
schema: the fields it has, which are required, and which blocks and Molang expressions it holds.
Editing the form writes the file.
- Search (
Find a feature, top left) matches identifiers, types and filenames, and tells you
what is wrong with a hit before you click it.
- Right-click empty canvas to create a feature. The menu only offers what the engine can
actually build at your pack's
format_version.
- Groups — select several cards,
Ctrl+G, and they become one named card you can fold and
unfold. The grouping lives in the pack files, so it is yours and your team's, not a local
setting. Groups are never guessed at: a group exists because somebody made it.
- Patterns in the create menu place several features wired together in one step — a loop, a
column, a placement guard — for shapes the type list has no single entry for.
Every section of the form has a ? that opens what that field does, in plain words.
The 3D preview
Ctrl+Alt+P runs the feature into a small world generated for the purpose and shows you the
result. Saving the file re-renders it.
The sidebar controls the run:
| Section |
What it is for |
| Feature / Rule |
Which feature to place, where, and how many times. A rule preview runs the rule's own distribution across the chunks it would decorate. |
| Environment |
The world to place into: ten terrain presets, from plains to nether to an empty void, and the size of the volume. |
| Materials |
What the terrain is made of, so a feature that only attaches to one block can be tested without editing the pack. |
| Biome |
A pack biome to run under, or a hand-written tag list, for features gated on biome tags. |
| Budget |
Limits on writes, delegations and wall-clock time, so a feature that references itself truncates instead of hanging. |
| View |
Slice by height, hide the surrounding terrain, colour cells by write count, frame the camera. |
| Diagnostics |
Everything the run declined to do, and why — with the delegation chain that reached it and a button that moves the camera there. |
If the preview comes back empty, Diagnostics is where the reason is. The documentation site's
When the preview shows nothing
page lists every reason the engine can give.
Ctrl+click (Cmd+click) a places_feature or features entry in the JSON to jump to the file that
defines it.
When something goes wrong
Every command shows what step it is on and leaves a spinner in the status bar while it runs. On a
big pack the engine's own progress joins that line — the phase it is in, how many files it has
read, and a second count that keeps moving — so a long load reads as work rather than as a hang.
Every failure ends in a short message with a Show log button.
Run Feature Lab: Show Log for the whole story: which engine executable was chosen and its
version, the pack root it worked out, how long each step took, and everything the engine wrote,
verbatim. Load-time problems also appear as squiggles in the JSON and in the Problems panel.
Settings
| Setting |
Default |
What it does |
featurelab.binaryPath |
(empty) |
Path to the engine executable. Leave empty to use the bundled copy; set it to point at a local build. |
featurelab.requestTimeoutMs |
30000 |
How long the engine may go silent before a request is given up on — not how long the request may take. The engine reports progress once a second on anything slow, and each report buys another full wait, so a pack that needs a minute to load is never cut off while it is visibly working. Raising the panel's own placement time limit raises this with it. |
featurelab.env |
plains |
Which environment preset a new panel starts on. |
featurelab.blockTextures |
true |
Prepare real block textures for the preview. The first preview asks once whether to fetch Mojang's sample resource pack (about 150 MB, cached outside your pack); declining is remembered. Turning it off means nothing is fetched, built or asked about. Whether textures are actually drawn is the preview sidebar's own Block textures switch, which remembers what you choose; either one off leaves the preview in flat colours, and it says which. |
What a preview is, and is not
The preview is a bench, not the game. It places one feature into a world it generated for the
purpose, so it can show that feature in isolation and say why a placement failed. It does not
generate a real chunk: no other feature runs beside yours, and nothing here proves the same JSON
behaves identically in Minecraft.
Where the two are known to differ, the tool says so — in a diagnostic when it affects your file,
and in the documentation site otherwise. That site
carries a page per feature type and a
coverage page
listing every known gap. It is the honest place to start when a preview and the game disagree.
Requirements
VS Code 1.85 or newer. Nothing else.
