Open CASCADE Technology (OCCT) is an object-oriented C++ class library designed for rapid production of sophisticated domain-specific CAD/CAM/CAE applications.


A typical application developed using OCCT deals with two or three-dimensional (2D or 3D) geometric modeling in general-purpose or specialized Computer Aided Design (CAD) systems, manufacturing or analysis applications, simulation applications, or even illustration tools.

Companies choose Open CASCADE Technology because of its strong competitive advantages over other CAD kernels.


No license fees

Software vendors choose Open CASCADE Technology because it can be used free of charge, and with no limitation as to the number of installed copies, meaning a greatly reduced cost of solutions based on it. Absence of license fees reduces costs of evaluation period, prototyping and piloting projects.

Access to source code

CAD/CAM/CAE software developers who need full control over the quality, stability and robustness of their applications choose Open CASCADE Technology because they can access its high-quality code. The users of Open CASCADE Technology can freely adapt, modify and enrich its source code by necessary functionality according to their particular needs.

Product continuity

Software vendors who care about the longevity of their products use Open CASCADE Technology because its permanent evolution and continuity are ensured by OPEN CASCADE, our industrial customers maintaining their own Open CASCADE Technology based solutions, and the worldwide community of Open CASCADE Technology users.


Companies which pay significant attention to the quality of their software develop with Open CASCADE Technology because its increasing quality and robustness is ensured by the Initial Developer (OPEN CASCADE). A large community of industrial users and customers are constantly testing the software thus helping OPEN CASCADE maintain a high level of quality and robustness of Open CASCADE Technology.

Openness and interoperability

Software vendors requiring their products to provide easy connection with other CAD/CAM/CAE software used by their customers prefer Open CASCADE Technology because it provides wide data exchange possibilities, both through neutral formats and directly with CAD systems. This enables an open, long-term viability of the solutions based thereupon. Learn more about the companies that have already chosen Open CASCADE Technology to empower their projects on a page dedicated to Our Customers.

OCCT library is designed to be truly modular and extensible, providing C++ classes for:

  • Basic data structures (geometric modeling, visualization, interactive selection and application specific services);
  • Modeling algorithms;
  • Working with mesh (faceted) data;
  • Data interoperability with neutral formats (IGES, STEP);

The C++ classes and other types are grouped into packages. Packages are organized into toolkits (libraries), to which you can link your application. Finally, toolkits are grouped into seven modules.

This modular structure is illustrated in the diagram below.

  • Modeling Data module supplies data structures to represent 2D and 3D geometric primitives and their compositions into CAD models;
  • Mesh module implements tessellated representations of objects;
  • Visualization module provides complex mechanisms for graphical data representation;
  • Data Exchange module inter-operates with popular data formats and relies on Shape Healing to improve compatibility between CAD software of different vendors;
  • Application Framework module offers ready-to-use solutions for handling application-specific data (user attributes) and commonly used functionality (save/restore, undo/redo, copy/paste, tracking CAD modifications, etc.).

In addition, Open CASCADE Test Harness, also called Draw, provides an entry point to the library and can be used as a testing tool for its modules.