How to write prompts that print

1. Describe the parts, not the name

A name tells the image model what category you mean. A parts list tells it what the object should actually look like.

Text jobs first make a reference picture, then turn that picture into a mesh. If the picture is wrong, the model will be wrong too.

2. Think like a printer

Ask for geometry that can survive slicing, supports, removal from the bed, and real-world handling.

• Chunky limbs and sturdy connections
• No thin spikes or floating parts
• A flat base that touches the bed
• Sitting or perched poses
• One clear object
• A plain background

3. Pick the right engine

4. Pro move — make the picture first

Generate your reference picture in any image tool you like, such as ChatGPT, Gemini, Grok, or Midjourney. Check that the front view looks right, then bring it into the Image tab for 10 or 25 credits.

This gives you more control and usually means fewer re-rolls. Text prompts also include one free re-roll per model if the first result isn't right — image uploads don't, since the model is built straight from your photo. You can even discuss and refine the prompt with an AI assistant before making the picture.

5. Ultra move — show all four sides

Prepare front, back, left, and right views of the same reference. Upload all four so the engine does not have to guess what the hidden sides should look like.

Ultra also runs Detail Forge on our premium engine, which brings out sharper detail on complex models — same credit cost as Pro.

6. Set your size before download

Use the Target size box in Prepare print before downloading. STL files do not carry units, and slicers assume the numbers are millimeters. Forge STL scales the longest edge to your chosen size, turns the model Z-up, and seats it flat on the bed.

Getting the size right

Proportions belong in the prompt — say a foot is roughly 1.3x wider than it is tall, or that limbs are chunky. Do not put millimeters in the prompt.

Real-world size is set once, in Target size, just before you download. Pick your printer there and Forge STL keeps the longest edge inside your bed.

What you can't prompt

Every prompt is checked before it runs. Not allowed: nudity or sexual content, gore and torture imagery, hate symbols, real identifiable people, illegal items, and mockery or defacement of religious figures or symbols of any faith. Respectful religious and devotional pieces — crosses, Buddha statues, menorahs, nativity scenes — are welcome, and so is ordinary fantasy and horror like dragons, skulls and monsters.

Full details are in the Prohibited content section of our Terms. Blocked prompts never cost credits.