OpenCascade
CAD kernel in Developer tools
Free open-source B-rep CAD kernel that people recommend for STEP export and solid modeling. Critics say it trails commercial kernels like Parasolid in robustness and features.
Free open-source B-rep CAD kernel that people recommend for STEP export and solid modeling. Critics say it trails commercial kernels like Parasolid in robustness and features.
29 people gave an opinion
- recommend it
- 15
- criticize it
- 14
- approval share
- 52%
Recommended in 6 of 13 months
- November 2025: recommended
- December 2025: not recommended
- January 2026: recommended
- February 2026: not recommended
- March 2026: recommended
- April 2026: recommended
- May 2026: recommended
- June 2026: not recommended
- July 2026: not recommended
- August 2026: not recommended
- September 2026: not recommended
- October 2026: recommended
- November 2026: not recommended (month in progress)
Why it doesn’t carry the badge
- 15 people recommend itNeeds 10 or more, met.
- 1 recommender for every criticNeeds 2 to 1 or better, not met.
- Recommended in 6 of 13 monthsNeeds 4 or more, met.
The same three rules apply to every product, and the badge can’t be bought. How the badge works
What people say about it
The reasons people give, with the number of comments that give each one. Open a reason to read what they said.
Why people recommend it
Each mark is one comment
Capable B-rep modeling kernel
“one of the only B-Rep CAD kernels available which is free and open source”
Comment from 18 May 2026 in “GenCAD” “OpenCascade's (fickle but otherwise lovely) BREP modeling”
Comment from 24 Mar 2026 in “Dune3d: A parametric 3D CAD application” “OCCT is more than capable for what FreeCAD is offering”
Comment from 26 Mar 2026 in “FreeCAD Version 1.1 Released” - Comment from 31 Mar 2026 in “Open source CAD in the browser (Solvespace)”
Broad range of operations
“for boolean operations I didn't find it to be a decade behind at all”
Comment from 28 Oct 2026 in “Show HN: Nasscad – local-first 3D CAD for browser and Windows” “pretty good range of operations supported”
Comment from 10 Apr 2026 in “Show HN: FluidCAD – Parametric CAD with JavaScript” Lovable despite fickle behavior
“OpenCascade's (fickle but otherwise lovely) BREP modeling”
Comment from 24 Mar 2026 in “Dune3d: A parametric 3D CAD application” “fickle but otherwise lovely”
Comment from 23 Mar 2026 in “Dune3d: A parametric 3D CAD application”
What people warn about
Each mark is one comment
Behind commercial kernels like Parasolid
“Which I really appreciate, but let's be real, it is far behind eg. parasolid.”
Comment from 31 Mar 2026 in “Open source CAD in the browser (Solvespace)” “is both less sophisticated today and is slower to gain new features than Parasolid”
Comment from 20 Feb 2026 in “FreeCAD is an open-source parametric 3D modeler” “OCCT's boolean/blend engines aren't really as robust as the commercial kernels”
Comment from 13 Oct 2026 in “Show HN: SolidCraft – Open-Source Parametric CAD in Rust (With MCP Support)” - Comment from 18 May 2026 in “GenCAD”
- Comment from 20 Feb 2026 in “FreeCAD is an open-source parametric 3D modeler”
- Comment from 22 Feb 2026 in “FreeCAD is an open-source parametric 3D modeler”
Fails on fillets and complex geometry
“as your geometry gets more complicated you start running into the kernel limitations”
Comment from 31 Mar 2026 in “Open source CAD in the browser (Solvespace)” “fillets cannot consume connected faces and may fail for a number of other reasons”
Comment from 18 Nov 2025 in “Blender 5.0” “OCC will fail on cases that Parasolid handles without complaint”
Comment from 20 Feb 2026 in “FreeCAD is an open-source parametric 3D modeler” - Comment from 25 Mar 2026 in “Dune3d: A parametric 3D CAD application”
Architecture limits and integration difficulty
“Freecad is limited by Open Cascade which is the modeling kernel at the heart of the program.”
Comment from 26 Mar 2026 in “FreeCAD Version 1.1 Released” “It just sucks that they are stuck with the OpenCasacade kernel”
Comment from 25 Mar 2026 in “FreeCAD Version 1.1 Released” “known for being notoriously difficult to integrate”
Comment from 11 Oct 2026 in “OpenSCAD the Programmers Solid 3D CAD Modeller” - Comment from 28 Oct 2026 in “Show HN: Nasscad – local-first 3D CAD for browser and Windows”
Topological naming problem worsened by design
“the design of its API is part of why the topological naming problem was so difficult to mitigate”
Comment from 22 Nov 2025 in “Blender 5.0” “the Topological Naming Problem (as I understand it) is made quite bad due to OpenCASCADE design”
Comment from 30 Jan 2026 in “Netflix Animation Studios Joins the Blender Development Fund as Corporate Patron” “OpenCascade doesn't maintain any naming across its interfaces at all”
Comment from 24 Nov 2025 in “µcad: New open source programming language that can generate 2D sketches and 3D”
What people recommend instead
The same counts for each, so you can compare like for like. The tick on each bar marks the 2 to 1 line the badge needs.
| Product | Recommend | Criticize | Approval | Months | Owned | Badge |
|---|---|---|---|---|---|---|
| OpenCascadeThis page | 15 | 14 | 52% | 6 | — | — |
| Parasolid | 8 | 2 | 80% | 5 | — | — |
What people said
33 of the 35 comments that mention it, newest first. Each links to the original comment.
“for boolean operations I didn't find it to be a decade behind at all”
“they are limited by OpenCascade's architecture”
“OCCT's boolean/blend engines aren't really as robust as the commercial kernels”
“known for being notoriously difficult to integrate”
“of a bRep kernel better than Opencascade”
“OpenCASCADE is less capable than Parasolid”
“all significantly worse than commercial kernels like Parasolid or ACIS”
“one of the only B-Rep CAD kernels available which is free and open source”
“There's a lot of alpha to be had in experimenting with LLMS and writing OCCT kernel cad code imo”
“pretty good range of operations supported”
“as your geometry gets more complicated you start running into the kernel limitations”
“Which I really appreciate, but let's be real, it is far behind eg. parasolid.”
“the engine is not as capable as OpenCascade.”
“OCCT is more than capable for what FreeCAD is offering”
“Compared to say OpenSCAD, Open CASCADE is leagues ahead.”
“the OpenCASCADE 8.0 release is very promising”
“Freecad is limited by Open Cascade which is the modeling kernel at the heart of the program.”
“It just sucks that they are stuck with the OpenCasacade kernel”
“OpenCascade causes its own geom issues too”
“OpenCascade's (fickle but otherwise lovely) BREP modeling”
“fickle but otherwise lovely”
“OpenCASCADE is less refined than parasolid”
“is both less sophisticated today and is slower to gain new features than Parasolid”
“OCC will fail on cases that Parasolid handles without complaint”
“the Topological Naming Problem (as I understand it) is made quite bad due to OpenCASCADE design”
“the Open CASCADE CAD kernel is a huge mess”
“OpenCascade doesn't maintain any naming across its interfaces at all”
“the design of its API is part of why the topological naming problem was so difficult to mitigate”
“If one wants to export STEP then definetly use OpenCASCADE”
“You can totally start with OpenCascade.”
“OpenCascade's kernel forces you to deal with periodicity in topology”
“Some of these issues are long standing and really hard to solve”
“fillets cannot consume connected faces and may fail for a number of other reasons”
Counts come from 1,795,640 Hacker News comments, November 2025 to November 2026. How we count. Report a mistake.