How to use text-to-CAD: a practical starter guide

Last Tuesday I had fifteen minutes before a call and a bracket I needed roughed out. Nothing fancy. A flat plate with standoffs and four countersunk holes. The kind of part I've modeled a thousand times in Fusion 360, and the kind of part that takes exactly long enough to be annoying when you're in a hurry. So I opened Zoo.dev, typed a sentence, and hit generate. Twelve seconds later I had a STEP file on my desktop. It wasn't perfect. Two of the hole positions were off by about a millimeter and the standoff height was close but not what I asked for. But it was a starting point, and that starting point got me to a finished part in about four minutes instead of twelve.

That's what using text-to-CAD actually looks like. Not magic. Not a finished part falling from the sky. A rough first draft that you clean up, the same way you'd clean up a sketch from a napkin except the napkin is three-dimensional and already has most of the features in the right place.

If you've read the text-to-CAD guide and want to know how to actually sit down and do this, here's the practical version.

Pick your tool#

There are several text-to-CAD tools out there now, and they work differently enough that the choice matters. For a full comparison, the best text-to-CAD tools post covers each one in detail. For getting started, you really only need to know about two.

Zoo.dev is the most straightforward option. It's browser-based, it outputs real B-Rep geometry as STEP files, and the free tier gives you enough generations to actually learn the tool before deciding if it's worth paying for. You type a prompt, the AI generates a solid model, and you download the result. No install, no plug-in, no API key required for basic use.

CADAgent is the other one worth trying, especially if you already live in Fusion 360. It's an open-source add-in that generates parametric models directly inside Fusion, complete with a real timeline you can roll back and edit. The catch is you need an Anthropic API key, which means setting up an account and paying per-generation. The upside is the output has actual feature history, not just an orphaned solid sitting in the browser tree.

For your first session, I'd start with Zoo. Lower friction, faster feedback loop, and you can evaluate the output in whatever CAD software you already use.

Write a prompt that's actually specific#

This is where most people fail on the first try, and honestly where I failed too. The instinct is to write something like "make me a bracket" and expect the AI to read your mind. It won't. The AI has no idea what bracket you're imagining. It's going to give you its average bracket, which will look vaguely bracket-shaped and be dimensionally wrong in ways that are hard to fix because the proportions weren't what you wanted in the first place.

Good prompts include dimensions, feature names, and constraints. Bad prompts are vague descriptions that could mean fifty different parts.

Here's a bad prompt: "A mounting bracket for a sensor."

Here's a better one: "An L-shaped mounting bracket, 3mm thick aluminum. Vertical leg 40mm tall, 30mm wide. Horizontal leg 50mm long, 30mm wide. Two 4.2mm through-holes on the vertical leg, centered horizontally, spaced 20mm apart vertically, first hole 10mm from the top. Two 4.2mm through-holes on the horizontal leg, centered across the width, spaced 30mm apart, first hole 10mm from the bend. 2mm fillet on the inside corner of the bend."

The second prompt is longer. It's also the one that produces a usable part. I've written more about this in text-to-CAD prompt engineering, but the core principle is simple: every dimension you leave out is a dimension the AI gets to guess, and it will guess wrong often enough to annoy you.

Specify dimensions in millimeters. Name standard features (counterbore, chamfer, fillet, boss, pocket) by their proper names. Describe one part at a time. If you need an assembly, generate each part separately. None of the current tools handle multi-part assemblies well, and trying to describe two mating parts in one prompt produces geometry that looks like the AI had a stroke.

Generate and wait#

This part is the easy part. In Zoo, you paste your prompt into the text field and click generate. The server does its thing for somewhere between five and thirty seconds depending on complexity, and then you get a preview of the model plus download options.

In CADAgent, you type the prompt in the add-in panel inside Fusion 360 and watch the model build itself in real time. Sketches appear, extrusions happen, fillets get applied. It's genuinely entertaining the first few times and then you start paying attention to whether the operations make sense.

Either way, you're waiting for the AI to interpret your words as CAD operations and execute them. The translation from natural language to geometry is where the interesting failures happen, and why the text-to-CAD tutorial walks through the full process with a real example.

Inspect the output before you trust it#

This is the step people skip, and it's the step that matters most.

Whatever the AI generated, do not assume it's correct. Open the file. Measure things. Check the hole diameters. Verify the overall dimensions. Look at the topology. Rotate the model and check for surfaces that shouldn't be there, internal faces, zero-thickness geometry, or features that look right from one angle and wrong from another.

I have a short checklist I run through on every text-to-CAD output:

1. Overall bounding box dimensions: are they what I asked for?
2. Hole diameters and positions: are they where I specified?
3. Feature presence: did it include everything I mentioned?
4. Feature absence: did it add things I didn't ask for?
5. Topology: is it one clean solid body, or are there extra surfaces hiding inside?
6. Edge quality: do the fillets and chamfers look clean, or are there tangency breaks?

On a simple plate with holes, maybe half of these checks catch something. On anything more complex, at least one or two will reveal a problem. The holes might be 4mm instead of 4.2mm. A fillet might be missing. The overall height might be 38mm instead of 40mm. These are the kinds of errors that text-to-CAD produces reliably, and they're also the kinds of errors that are easy to fix if you catch them and expensive to miss if you don't.

Export as STEP#

If you're working in Zoo, you'll download the result as a STEP file. This is the format you want for engineering work. STEP (ISO 10303) preserves B-Rep geometry with real faces and edges that any professional CAD software can import and edit. Avoid STL unless you're going directly to 3D printing and don't care about editing the model further.

If you're in CADAgent, the model is already in Fusion 360, so export isn't an issue. You can save it as a native Fusion file, export to STEP, or work with it directly.

The file format question matters more than people think. I've seen newcomers download an STL from a text-to-CAD tool, try to edit it in SolidWorks, and spend an hour wondering why they can't select a face. An STL is a bag of triangles. You can't fillet a bag of triangles. Get the STEP file.

Import and fix in your CAD software#

This is where the real work starts, and I mean that in a good way. The text-to-CAD tool gave you a first draft. Now you turn it into a real part.

Open your STEP file in Fusion 360, SolidWorks, or whatever you use. The geometry will appear as an imported body without parametric history (unless you used CADAgent, in which case you already have a timeline). From here, you're doing normal CAD work: adjusting dimensions, adding features, fixing things the AI got wrong.

Common fixes I end up making on text-to-CAD output:

Hole positions. Almost every part I've generated has at least one hole that's off by half a millimeter to a couple of millimeters. I measure, delete the hole, and redrill it where it should be. This takes about thirty seconds per hole.

Missing features. The AI sometimes drops features from the prompt, especially if the prompt is long. A fillet it didn't apply, a chamfer it forgot about, a counterbore that came out as a through-hole. I add these manually.

Dimensional corrections. Overall dimensions are usually close but not exact. If I asked for 80mm and got 78.5mm, I'll sketch on a face and use the move/extend body command to fix it, or just model the correct geometry and use combine/cut to clean it up.

Topology cleanup. Occasionally the imported body has internal surfaces or non-manifold edges that cause problems downstream. Running a body repair or manually deleting the offending surfaces usually handles this.

The whole import-inspect-fix cycle takes me about five to fifteen minutes on a simple part. On anything complex enough that the AI got most of it wrong, I just start over from scratch in CAD. Knowing when to fix the AI output and when to throw it away is a skill you develop after a few sessions.

The workflow in practice#

Here's what a realistic text-to-CAD session looks like for me now, after a few months of using these tools.

I have a part in my head. Something simple to moderate: a bracket, an enclosure wall, a mounting plate, a spacer, a cable clip. I open Zoo.dev. I spend about sixty seconds writing a specific prompt with all the dimensions I care about. I generate. I download the STEP. I open it in Fusion 360. I spend two minutes inspecting and three to eight minutes fixing. Total time: five to twelve minutes. Compare that to modeling from scratch, which for the same class of parts takes me eight to twenty minutes depending on complexity.

The savings are real but modest for simple geometry. Where text-to-CAD actually saves more time is when I'm exploring variations. Need to try five different bracket configurations to see which one fits best in the assembly? Five prompts in Zoo take maybe three minutes total. Five models from scratch in Fusion take thirty minutes minimum. That iteration speed is where the tool earns its keep.

For anything involving complex surfacing, tight tolerances, sheet metal with bend logic, or parts that need to mate precisely with other components, I don't bother with text-to-CAD. I model those from scratch because the cleanup time exceeds the generation time, and the AI has no concept of manufacturing constraints. Nobody's taught these models what a K-factor is, and it shows.

What to expect when you're starting out#

Your first few text-to-CAD attempts will probably produce garbage. Not because the tools are bad, but because writing good prompts is a skill and you don't have it yet. I didn't either. My first prompt was something like "a box with a hole in it" and I got back a box with a hole in it that was dimensioned like the AI had never seen a real object.

Give yourself an afternoon. Try ten or fifteen prompts. Start with the simplest parts you can think of: a rectangular plate, a cylinder with a hole, a basic L-bracket. Get a feel for how the tool interprets your words. Notice which details matter (dimensions, feature names, positions) and which ones the AI ignores (material suggestions, manufacturing intent, anything vague).

Read the text-to-CAD prompt engineering post before you sit down. It'll save you the worst of the learning curve.

The gap between "my first prompt" and "I can reliably get useful output" is about two hours of practice. After that, you'll know the tool's limits and you'll know when it's faster to type a prompt versus just modeling the thing yourself. That judgment is the real skill here, not the typing.

Where text-to-CAD fits in real work#

Text-to-CAD is a starting tool, not a finishing tool. It generates first-draft geometry that you edit into a real part. It's fastest for simple prismatic shapes with standard features. It's useless for complex assemblies, organic surfaces, or anything requiring manufacturing-specific logic.

If you're expecting it to replace knowing how to use CAD, it won't. If you're expecting it to save you ten minutes on a bracket, it probably will. That's not a revolution. It's a time saver that works when the geometry is simple and the expectations are realistic.

I keep a shortcut to Zoo.dev pinned in my browser. I use it maybe three or four times a week, almost always for the same kind of thing: a simple part I don't feel like sketching from scratch when I already know exactly what it should look like. It doesn't replace my CAD skills. It just means I spend less time on the parts that don't need my full attention, and more time on the parts that do.