AI for CAD Tools
Free text to CAD tools compared on output type, free-plan limits and license terms, plus a CadQuery test of what STEP keeps and STL loses.
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6 min read
Michelle Ben-David
Michelle Ben-David is a mechanical engineer and Technion graduate. She served in an IDF elite technology and intelligence unit, where she developed multidisciplinary systems integrating mechanics, electronics, and advanced algorithms. Her engineering background spans robotics, medical devices, and automotive systems.
BOTTOM LINE
For a free text to CAD tool that returns a solid you can machine, start with Zoo Design Studio's Free plan or have a chat model write CadQuery code that exports STEP. Free mesh tools such as Meshy suit concept prints and shape reviews only. Leo fits once the parts must join a team's existing vault and assemblies.
The free text to CAD options that return a solid you can machine are Zoo Design Studio's Free plan and the code route: a chat model writes CadQuery code that exports STEP. Meshy's free plan returns meshes under a CC BY 4.0 license, which suits concept prints only.
If you are a design engineer pricing a tool before your manager signs a purchase order, the free tier has to prove 2 things: the output survives your CAD and CAM, and the limits allow a real test. This guide compares 4 free options, plus one paid option, from vendor documentation read on 2026-11-11.
Four checks decide whether a free tool is usable for parts
Run each free option through these 4 checks in order. A tool that fails the first one is out, whatever its price:
Output type. A STEP file holds a boundary-representation (B-rep) solid with true cylinders and planes. An STL, OBJ or GLB file holds flat triangles, so hole sizes and volumes come out approximate.
Editability. A feature tree or a script lets you change one dimension and rebuild. A generated mesh has no parameters to change.
Free allowance and what happens at the limit. Count what the free plan allows per month, and check whether work stops or bills you when it runs out.
License and data terms. Read what the free plan lets you do with the output. Meshy's free plan, for example, requires attribution for commercial use.
For a team, checks 3 and 4 weigh more than for one person. A free allowance sized for 1 user will not cover a trial by 10 engineers, and a design described in a prompt leaves your network.
IN PRACTICE
The geometry search has been invaluable, helping me find standard parts instead of designing new ones, saving a huge amount of time and effort. The search system is smart and CAD-aware.
- eytan s., R&D Engineer
Four free options and Leo side by side
Each row below comes from the vendor's own pages, read on 2026-11-11:
Option | What it does | Where it runs | Output | Free allowance | Data it can reach | Best for |
|---|---|---|---|---|---|---|
Zoo Design Studio, Free plan | Zookeeper agent turns text, images and sketches into parametric KCL models | Zoo Design Studio desktop app | Editable KCL model; STEP or STL export | Unlimited manual CAD modeling; Zookeeper reasoning time is metered monthly, Auto mode only | The active project only | One engineer modeling new parts from scratch |
Meshy, Free plan | Text to 3D creates a mesh, then a refine step textures it | Web app and API | GLB, OBJ, FBX, STL or USDZ mesh | 100 credits a month, up to 10 assets, 1 task at a time | The prompt or image you send | Concept visuals and display prints |
CadQuery plus a chat model | The chat model writes Python; CadQuery builds the solid on the OpenCascade kernel | Your own machine | STEP, STL, AMF or 3MF | No limit from CadQuery; the chat model's own plan applies | Whatever you paste into the prompt | Prismatic parts you can describe with dimensions |
OpenSCAD plus a chat model | The chat model writes OpenSCAD script; OpenSCAD compiles it with CSG | Your own machine | STL or OFF for 3D models | No limit from OpenSCAD (GPL version 2) | Whatever you paste into the prompt | 3D printed fixtures and spacers |
Leo | Generates parts from text, images and drawings, and finds existing parts first | Desktop and web app with a CAD add-in | Solid body with an editable feature tree in SolidWorks, Creo, Inventor or Onshape; STEP or STL export | No generic free trial; a demo runs on one of your own parts | Your CAD files and vault data through PDM and PLM integrations | Parts that join an existing assembly |
Zoo and CadQuery export STEP, and Leo builds a native solid in your CAD. Meshy and OpenSCAD return meshes, so they fail check 1 for any machined part.
How each free option scores on the four checks
Each verdict below is based on the vendor's own documentation, plus one CadQuery run on 2026-11-11 shown in the table at the end of this section.
Zoo Design Studio. The Zookeeper FAQ lists STEP or STL exports, and the model is stored as KCL code, so each dimension stays editable. Zoo's pricing page says CAD modeling is unlimited while Zookeeper reasoning time is metered, and billable usage pauses by default when it runs out. The limit is reach: Zookeeper cannot read files outside the active project.
Meshy. The Text to 3D API returns an untextured mesh first, in GLB, OBJ, FBX, STL or USDZ. The Free plan gives 100 monthly credits and licenses output under CC BY 4.0, which requires attribution; the Pro plan switches to a private license. Use it for a shape review, then model the part in CAD.
CadQuery plus a chat model. CadQuery runs on the OpenCascade kernel and writes STEP, AMF, 3MF and STL. The chat model writes the script, so the free part is only as good as the dimensions in your prompt. You still check every hole and wall yourself.
OpenSCAD plus a chat model. OpenSCAD compiles a script into a solid using constructive solid geometry and 2D extrusion. Its About page lists STL and OFF as its 3D file formats, so the export lands in the mesh column even though the script is parametric.
To see what check 1 means in numbers, we ran a CadQuery script for a 100 x 60 x 6 mm plate with 4 holes of 5.5 mm diameter, 10 mm in from each edge (CadQuery 2.8.0). We compared the exported files against the hand-calculated volume of 35,429.80 mm³:
Export | Triangles | Volume (mm³) | Error vs hand calculation |
|---|---|---|---|
STEP (B-rep) | none | 35,429.80 | 0.00 mm³ |
STL, 0.1 mm tolerance | 444 | 35,435.33 | +5.53 mm³ |
STL, 0.01 mm tolerance | 2,044 | 35,430.04 | +0.24 mm³ |
The STL error comes from the flat facets that approximate each hole. Tightening the tolerance cut it by a factor of 23, but the file grew from 22 KB to 102 KB and the holes are still polygons.
Run a two-week trial on three of your own parts
Pick 3 released parts your team knows well: one prismatic bracket, one turned part and one sheet metal part. Then run each free option through these steps:
Days 1 to 2: write one prompt per part from its drawing, with every critical dimension and tolerance in the text. The prompt guide shows how to phrase dimensions.
Days 3 to 5: generate each part and export STEP where the tool offers it. Record whether you hit the free allowance and on which part.
Days 6 to 8: import each file into your release CAD. Pass if it opens as a solid body, not a mesh or a surface set.
Days 9 to 11: measure 5 critical features per part against the drawing. Pass if all 5 fall inside the drawing tolerance.
Days 12 to 14: change one driving dimension in the tool and regenerate. Pass if the part rebuilds without a new prompt.
A tool that passes steps 3 to 5 on all 3 parts has earned a paid-plan quote. The accuracy and precision post lists more checks for production parts.
The same trial run with Leo on your own parts
Leo has no free tier to test, so the trial runs as a demo on one of your own parts instead. Send the same 3 drawings from the trial above. Leo works from each drawing and asks you for missing dimensions before it models anything. The result lands natively in SolidWorks, Creo, Inventor or Onshape as a solid body with an editable feature tree. Steps 3 and 5 of the trial then run on a native file, not an import.
Before it generates anything, Leo searches your internal library and PLM for a part with the same shape. Leo offers integrations with leading PDM and PLM platforms (SolidWorks PDM, Autodesk Vault, PTC Windchill, Siemens Teamcenter, Arena PLM, and others).
Leo indexes the newest revision of each file with no check-out, limited to the folders your admin selects. If the bracket on drawing 1 already exists as a released part, the answer is that part number, not a new model. See how shape search finds parts by geometry.
One limit: Leo needs a connected CAD system or vault to show its full value, so a demo with no files of yours shows less. The security page covers how your files are handled.
FAQ
Zookeeper text-to-CAD and FAQ, Zoo, accessed 2026-11-11
Pricing, Zoo, accessed 2026-11-11
Text to 3D API, Meshy, accessed 2026-11-11
Pricing, Meshy, accessed 2026-11-11
Introduction, CadQuery documentation, accessed 2026-11-11
About OpenSCAD, OpenSCAD, accessed 2026-11-11
FAQ, Zoo documentation, accessed 2026-11-11
Zookeeper in Zoo Design Studio, Zoo documentation, accessed 2026-11-11
FAQ, Leo AI, accessed 2026-11-11
Security, Leo AI, accessed 2026-11-11
See Leo on One of Your Own Parts
Bring a part or drawing and an applications engineer will run it live.
Send one part, drawing or text request from a current project. We show the editable model Leo builds in your CAD and any existing parts it finds first.
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