Writing Prompts
How to write prompts that produce predictable results — good and bad examples, beginner-friendly recipes, and material vocabulary.
You don't need any 3D background to write good prompts, but a few wording patterns swing the result dramatically. This page is a cookbook of recipes that work — same rules whether you're describing something new or editing an existing model.
Type a rough draft, optionally drop a screenshot of your current model (and a reference image of what you want), and a refined version comes back that you can copy straight into Thrixel. The widget applies the same rules described below.
Five rules that apply everywhere
1. Numbers beat adjectives. "Decimate to 50,000 triangles" works; "make it simpler" gambles. "Scale to 2 meters tall" works; "make it bigger" doesn't say how. If you can put a number on it, do.
2. Name the part, don't describe it. Once a model is generated, open the Scene Hierarchy panel — every named group (Body, Wheels, Chimney) is a handle you can refer to. Prompts that reference part names ("scale up the Wheels group by 1.5x") behave dramatically better than spatial guesses ("make the round things at the bottom bigger").
In the SPA, you can also click a part in the 3D viewer to scope an edit
to that part. A chip appears above the Edit prompt ("Apply to: Wheels"), and
when you Apply Edit, the LLM is told to leave every other part bit-identical.
Same applies to the Refine button — it'll rewrite your draft to stay within
that scope rather than expanding to the whole model. Via the API, pass
focus_on_node_names: ["Wheels"] on POST /api/v1/phase3/submit or
POST /api/v1/prompts/refine to get the same behaviour.
3. Anchor scale and direction to known things, not axes. "The size of a coffee mug" is unambiguous. "Facing the camera" beats "rotated 90° on Y" — forward / left / front / behind gets re-projected correctly more reliably than raw axes.
4. One change per edit. The single biggest mistake. If you say "make the wheels red AND raise the body AND add a roof", at least one of those three will silently revert or interact badly. Split into three sequential edits; editing is iterative by design.
5. "Keep X unchanged" is a real instruction. Without it, a small change can pull other parts along with it. Adding "keep the body, smokestack, and tender exactly as they are" ties everything else down.
Creating a model
A new-from-scratch prompt has to invent everything — geometry, proportions, materials, parts — so specifics buy you a lot. A useful prompt usually has three components:
- Subject — what the object actually is.
- Style — visual aesthetic (low-poly, stylized, realistic, voxel, cartoon).
- Scale anchor — a reference for size, if it matters.
Good
"A wooden barrel with iron rings, low-poly stylized, the size of a person."
Bad
"A cool barrel."
The bad version leaves style, materials, scale, and detail level entirely unconstrained. Each of those guesses will surprise you.
When you have a reference image
If you upload an image, the prompt's job changes — it describes intent, not appearance. Use the prompt to call out:
- The focus in the image (e.g. "model the dragon, ignore the background rocks").
- Anything the image doesn't show (e.g. "the back side has a tail similar to the front legs").
- Style overrides ("the image shows a real dog, but model it low-poly").
Good
"Model the central character only. Stylized hand-painted look. The arms not visible in the image should match the legs."
Bad
"Make this." (prompt is empty, image attached)
The empty-prompt case actually works okay most of the time, but framing is guessed and the entire scene sometimes gets modelled rather than the subject you cared about.
Style vocabulary
| What you want | What works in the prompt |
|---|---|
| Cartoon look | "stylized", "exaggerated proportions", "no surface detail", "flat colors" |
| Realistic look | "PBR materials", "photoreal", "fine surface detail" |
| Game-asset look | "low-poly", "stylized PBR", "clean topology" |
| Toy / blocky look | "voxel-style", "blocky geometry" |
| Specific colors | Hex codes (#a83232) or named colors ("dark forest green") |
Editing a model
Edit prompts are imperative — they describe what to change on top of the existing model. The structure is already known, so you can refer to specific named parts and they'll be matched.
Geometry edits
| Goal | Recipe |
|---|---|
| Reduce triangle count | Decimate the mesh so that there are 50000 triangles. |
| Uniform resize | Scale the entire model up by 1.5x. |
| Anisotropic resize | Scale only the height by 2x. Keep width and depth the same. |
| Move a part | Move the Chimney 0.3 units forward. Keep everything else unchanged. |
| Rotate a part | Rotate the Wheels group by 30 degrees. |
| Add a part | Add a small handle on the right side of the Body, near the top. |
| Remove a part | Remove the Antenna group entirely. |
| Smooth surfaces | Apply smooth shading to the Body and Roof groups. |
Color and material edits
| Goal | Recipe |
|---|---|
| Change one part's color | Make the Wheels red (#cc2222). Keep the Body color unchanged. |
| Change material type | Change the Body material from matte plastic to polished chrome. |
| Add an accent color | Add a thin gold trim around the rim of the Hat. |
Good
"Reduce the polygon count of the Body group to 8000 triangles. Keep the Wheels and Chimney unchanged."
Bad
"Make it less complex. Also bigger. And the wheels should be black."
The bad version mashes three unrelated edits into one prompt. Run them as three separate edits and you'll keep all three.
Common phrases that misfire
- "Make it look better" — there's no signal for what's wrong. Tell it.
- "Add more detail" — where? On which part? At what scale?
- "More realistic" — name the material instead ("rough cast iron", "polished chrome", "weathered painted wood").
- "A bit bigger" — give a number or a multiplier.
- "Like a [thing] but cooler" — describe the cool part directly.
Texturing — material vocabulary
When you're dialing in surface appearance (the Texture / Detailer steps), prompts are usually shorter — 2 to 6 words — and a reference image does most of the work.
Workflow tip
For texture work, paste or drop a screenshot of what you want before typing a prompt. The reference image dominates appearance; the prompt is a tiebreaker on material vocabulary. Long prompts without a reference image rarely beat short prompts with one.
These short phrases work better than full sentences:
| Surface | Phrase that works |
|---|---|
| Old / aged | weathered, oxidized, peeling paint, green patina |
| Smooth metal | polished chrome, brushed steel, gold leaf |
| Rough metal | cast iron, rusted steel, corroded bronze |
| Wood | rough wood grain, dark walnut, whitewashed pine |
| Stone | polished marble, weathered sandstone, mossy granite |
| Plastic / paint | matte plastic, glossy enamel paint, flat acrylic |
| Cloth / leather | worn leather, faded denim, quilted cotton |
| Glass / glow | frosted glass, tinted glass, glowing emissive panel |
Good
"Weathered bronze with green patina, especially in the recessed details."
Bad
"Make it look real and old."
Putting it together
A typical newbie-friendly flow:
- Create with a subject + style + scale anchor. Don't sweat materials yet.
- Auto-refine (no prompt) to clean up obvious geometry issues.
- Edit in one or more passes — one focused change per prompt, referencing part names from the Scene Hierarchy panel, with explicit "keep X unchanged" for everything you're not touching.
- Texture with a short material descriptor and (ideally) a reference image.
If something misfires, the fastest fix is almost always to shrink the prompt, not lengthen it.