Build from Reference

Build from Reference lets an AI assistant you connect to Creator build an object for you in the prefab workspace, out of the prefabs already in your Rust install, traced from a reference model or picture or from a description. You get an ordinary pack, made only of Rust’s own prefabs, that you place on a map like any other.

What you need

• Creator with a pack open in the prefab workspace (F4, or the PREFAB tab).
• An AI assistant connected to Creator: Claude Code or Claude Desktop. You bring your own account; Creator holds no key and calls no service.
• Something to build from: a 3D model, a picture, or only a description.

With no assistant at all, Fill Reference gives you a first draft from a 3D model on its own.

Which input works best

You give it	What the assistant works from
A 3D model (OBJ, STL, GLB or glTF)	The model’s real shape, as a reference in the workspace. This gives the closest result, because the assistant can read the shape exactly and check its work against it.
A picture (PNG or JPG)	The picture as a reference image, for its size and outline, plus its own view of the picture, which you also give it in your chat. Depth is the assistant’s estimate, so expect to correct it. A second picture from the side, stood upright and turned to face that way, gives it the depth too.
A description	No reference. The assistant takes its scale from the real sizes of Rust’s prefabs.

Whatever you give it, size the reference first: the size the reference has in the workspace is the size the object will have on a map. Size it from two points and a length you know, then tick Lock this reference so it cannot move while the assistant builds.

Start a build

1. Open the prefab workspace and open or start a pack.
2. For a model or a picture, add it under REFERENCE (Add Reference Model… or Add Reference Image…), size it and lock it.
3. In your assistant, start the Build from Reference prompt. In Claude Code, type /mcp__creator__build_from_reference, optionally followed by what you want built. Or ask in your own words: “Build the reference in the open pack out of Rust prefabs”.
4. When Creator shows the BUILD FROM REFERENCE card, read it and click ALLOW.

The assistant then reads the reference, writes a plan, places pieces, checks them, and keeps refining. A good first pass starts from cubes sized to fill the reference, then swaps them for real pieces (walls, stairs, roofs) where those read better.

The first time the assistant uses a prefab, Creator loads it from your Rust install before it can be placed, one prefab at a time. Some take longer than others. The assistant waits until Creator says the prefab is ready, then places it; you do not need to do anything.

The build session

One click lets the assistant build in this one pack until you stop it. Clicking ALLOW opens a build session: from then on its changes land without a card for each one. It can place, move, resize and remove pieces of the open pack, and nothing else: not another pack, not your map. Only modding cubes are resized; every other prefab keeps its own size.

While the session is open, the DOCUMENT panel shows a BUILD FROM REFERENCE block with how many changes the assistant has made, its plan in one line, what it assumed in planning, and the result of its last check, and a toast says when the session opens and when it ends.

The session ends when you:

• press STOP BUILDING in the DOCUMENT panel,
• save the pack,
• close the pack, or
• switch to another pack or to the map.

After that, the assistant has to ask again, with a new card.

The plan and the build check

Whatever it builds from, the assistant writes a plan before it places anything: the parts of the object, their sizes and materials, any doors and windows, and what holds each part up. Creator checks the plan and tells the assistant about a part resting on nothing, a part that does not touch what it rests on, or parts that overlap. A thin panel set flush on the side of the part that holds it, such as a window on a tower’s wall, hangs on that wall, and Creator says which face it hangs on. The plan lasts as long as the build session. It is not saved into the pack.

The plan can also list what the assistant had to guess, such as what holds the top up, how thick the walls are, or which side the door is on. Those guesses show in the DOCUMENT panel under the plan, one a line, so you can answer them. Building from a description, the assistant first pictures the plan as plain boxes, colored by material and with dark panels for the doors and windows, and lists its guesses before it places a single piece: correct the rough shape then, while it costs nothing.

After each batch, the assistant asks Creator to check the build. The check finds:

• pieces with nothing under them that reaches the floor,
• pieces barely held up, such as a wide slab balanced on one corner,
• pieces that overlap, and pieces a few centimeters apart that probably should touch,
• a build standing above the floor instead of on it,
• where the build differs from the plan.

With a 3D model reference in the pack, the check, and Creator’s reading of the model, also point out any part of the model that has nothing under it, so the assistant asks you about it instead of copying it. The DOCUMENT panel shows the plan in one line (how many parts, how tall and how wide), its guesses, and the result of the last check.

Your requirements, line by line

With the plan, the assistant writes down each thing you asked for, in your own words: how tall, how wide, how high a part stands (a deck at 12 m), how many posts, a door at the bottom, two windows on the front, what it is made of, what rests on what, hollow or solid, the same on both sides. Creator measures each one against what is actually built, not against the plan, and the DOCUMENT panel shows one line for each, your words first:

The line says	What it means
met	Creator measured it and the build has it, for example "15 m tall": met, 15 m tall.
not met	The build does not have it yet: the line says what Creator measured and how far off it is, for example "a post at each corner": not met, 3 of the 4 corners have a post.
not measurable	Creator cannot measure it yet, and the line says why, for example that nothing is built for that part yet.
not checked yet	The assistant has not checked the build since writing it down.

A line the assistant read off the reference rather than heard from you starts with From the picture: or From the model: instead of your words in quotes, so you can tell what you asked for from what it saw.

A requirement Creator cannot measure is never shown as met. The assistant keeps building until every line is met, or asks you about the one it cannot meet.

A door or a window counts whether it is open or filled: a gap you can see through, a Rust door or window prefab, a piece the plan names as a door or a window, or a panel of another material set flush into the wall, such as a wood door in a stone wall. A band of another material running the whole width of a wall is not a window.

Point at what to fix

To fix one part, select it in the workspace, then say what is wrong in your assistant’s chat: “make this wider”, “this should be wood”, “move this up a meter”. Select it the way you select anything in Creator: click it, Ctrl+click to add more pieces, or drag a box round them. There is nothing to type in Creator itself.

The assistant reads what you selected: the pieces, the part of its plan they build, the lines of your requirements they affect, and the pieces touching them or resting on them. It can also take its pictures with your selection outlined in orange, so it sees exactly what you mean; that outline is only in its picture, and your own view does not change. With nothing selected, it asks you to select the part first.

Then it changes what you pointed at, as one Ctrl+Z. Some fixes have to move something else: a door made wider narrows the wall beside it, and a part made taller lifts what rests on it. The assistant is never stopped from making that kind of fix, but nothing outside your selection changes silently: Creator tells it every piece outside your selection that the change moved, resized or removed, and how, so it can tell you.

Make it usable in Rust

By default the assistant builds from modding cubes, sized to match your reference exactly. Ask it to make the build usable in Rust (or game-ready) and it builds from the game’s own building pieces instead: foundations, walls, doorways, window walls, wall frames and floors, in the look you name (twig, wood, stone, metal or armored; stone if you name none), on Rust’s 3 m building grid. Rust builds in 3 m squares and 3 m stories, with half and low walls of 1.5 m and 1 m, and it has no pillar.

When a size you asked for does not fit the grid, the assistant asks you before it places anything. It asks once, with every size that does not fit and the grid sizes nearest to it, for example:

You asked for	You are asked
a 4 by 4 m shaft	3 by 3 m or 6 by 6 m?
a deck at 12 m, on a 1 m footing	10 m or 13 m?
four corner posts	open wall frames or full walls? (Rust has no pillar)
a 2 by 2 m cap	3 by 3 m?
a tower 15 m tall, with that deck, posts and a 1 m cap	14 m with the deck at 10 m and the cap as a 1 m course of low walls, or 17 m with the deck at 13 m and the cap as a 1 m course of low walls? (the top of the whole tower)

The whole build’s height is offered only at tops its parts can reach on the grid, each with the other answers it goes with, so the deck you choose also sets the top. If only leaving a part out would reach the height you gave, the question says so, and the part stays unless you say to leave it out.

A size you gave is never changed without asking you, whatever order you give things in. If the height you gave and the sizes you already settled disagree (say you gave the deck at 13 m first and 15 m tall later), the assistant asks again, naming both, for example “you said 15 m, but your deck at 13 m puts the top at 17 m; or 14 m with the deck at 10 m”. If they agree, nothing is asked. If you change the deck after choosing a height, you are asked the height again.

Your answer becomes the size it builds and the size your requirement line is measured against, and the line shows what you chose. A size you never gave is the assistant’s own choice, and it tells you the ones it made.

The whole build’s height is measured from the ground to its highest piece. The part of a foundation below the ground does not count, and everything above the ground does, a cap on the roof included.

A footprint is measured on the grid, by the squares the pieces fill. Rust’s walls and frames stand centered on the grid lines, so their own thickness reaches a little past the edge, and that does not count: a 6 by 6 m tower reads 6 by 6 m. A piece a whole square further out does count.

What rests on what is read the way Rust joins its pieces: a wall standing on a floor’s level rests on that floor, so a cap of low walls on the roof rests on the roof. A cap that stands past the roof’s edge, or above it, does not.

What you get in the game:

In the game	What it means
Solid and lasting	Players walk on the floors and stand behind the walls, and the pieces never decay.
Scenery, not a base	Nobody can damage it, upgrade it or build onto it with their own pieces.
Doorways open	Each doorway is left open: Creator does not place a door in a game-ready build yet.

Undo

Each batch of changes the assistant sends is one Ctrl+Z. Undo takes back the whole batch, however many pieces it placed or moved, and redo puts it back. Your own edits and the assistant’s sit in the same undo list, in the order they happened.

How the assistant checks its work

Besides the build check, the assistant checks a build two ways: by how much of the reference its pieces fill, and by pictures of the pack from the front, back, sides, top and a corner, with the reference shown or hidden. A picture shows only the pieces, the floor and walls, and the reference: never the gizmo, the origin marker or the scale post, and your selection only when the assistant asks to see it, as an orange outline. Taking those pictures does not move your view or change anything on screen. You can ask it to show you a picture, or point at a part that looks wrong.

A reference picture shows in those pictures as it does in your view: see-through, and hidden wherever a piece stands in front of it. When the build matches the picture closely, little of the picture is left to see but its background.

With a picture, Creator checks the build against what the picture shows. It finds the picture’s subject (what differs from the plain background along the picture’s edge; a drawn frame line round the edge is ignored), looks at the build the way the picture faces, and tells the assistant how much of the subject the build covers and how much of the build falls outside it, with a small picture of the difference. Both numbers allow one pixel where the picture’s edge is soft, so a build whose edges sit on the drawing’s scores 100 %; the exact numbers come with them. It also says where the picture stands and which way it faces. A build that matches a picture stands in front of it, its back on the picture: if the build is centered on the picture instead, the picture cuts through it and its back half looks faded, so Creator says how far to move it. With two pictures, a front and a side, each is checked on its own.

Creator can also picture the build from the reference’s own view, beside the reference: for a picture, square-on to it and framed exactly on it; for a 3D model, the model alone and the build alone from the front, the right, above and a corner, the same view for both. Each view comes with a picture of the difference (green where both are, red where the reference is and the build is not, blue where the build sticks out), how well the two outlines overlap, the places they differ most, and where their colors differ, such as a door that is brown in the picture and stone in the build. Lit stone and concrete come out as warm grays, often with warmer patches where single stones vary, and Creator counts them as gray, not brown. A build from a description has no reference to compare with; its requirements are what Creator measures it by.

What the assistant sees of a 3D model

Besides the model’s shape, the assistant reads what it looks like: each material’s name and color as the file gives them, the color as a plain word (such as stone gray or wood brown), and the name of any texture. It can also ask for a picture of the model alone, in its own colors, with no pieces and no see-through tint, from any of the same angles. That is how it picks pieces that look like the model, not only pieces of the right size. Creator draws the colors the file gives; a texture is named but not drawn, so a model that keeps all its look in textures shows as a plain shape.

Choosing pieces by look

Every prefab the assistant finds has a material word: stone, concrete, wood, metal, glass or other, read from its name and, once Creator has loaded it, from its materials. Each material of a 3D model reference gets the same word, so a model whose material is named stone leads the assistant to stone pieces. Asking for a material lists that material’s modding cubes first: a search for stone finds the tiled stone cubes before anything else.

The assistant can also look at up to six prefabs side by side in one picture, at their real sizes, before it chooses. That picture shows only those prefabs; nothing in your pack, your map or your view changes.

Save the pack

Nothing the assistant builds is kept until you save. Press Ctrl+S, or Save Prefab, as you would for any pack. Saving also ends the build session, so the assistant asks again before changing anything after that.

The saved .prefab holds only Rust’s prefabs. The reference is never saved into it; see what is saved, and where.

Without an assistant: Fill Reference

Fill Reference needs no AI. It fills a 3D model reference with modding cubes sized to it, in one click and one Ctrl+Z, so every user gets a usable first draft. You can stop there, refine it by hand, or ask an assistant to start from those cubes and replace them with real pieces.