What iLogic is
iLogic is Inventor's built-in rules engine. Rules are written in a VB.NET-based syntax with shortcuts for parameters, iProperties, features and components. Rules can live inside a part or assembly, or as external rules shared across files, and can run on events such as parameter changes or saves. Forms give users a simple interface.
If Parameter("Length") > 1000 Then
Feature.IsActive("Stiffener") = True
Else
Feature.IsActive("Stiffener") = False
End If
iProperties.Value("Project", "Part Number") = "BR-" & Parameter("Length")What the Inventor API is
The Inventor API is the full object model behind Inventor, available to add-ins written in C#, VB.NET or C++. Add-ins load with Inventor, add ribbon buttons and dialogs, respond to events, and can do everything iLogic can and much more: complex geometry, custom interaction, background processing and integration with other systems.
PartDocument part = (PartDocument)invApp.ActiveDocument;
Parameter length = part.ComponentDefinition.Parameters["Length"];
length.Expression = "1200 mm";
part.Update();In fact, iLogic rules can call the API directly through ThisApplication, so the boundary is not strict. The real difference is how the code is written, stored, deployed and maintained.
Side-by-side comparison
| Aspect | iLogic | Inventor API add-in |
|---|---|---|
| Who writes it | Engineers and designers | Software developers |
| Language | VB.NET-based rules | C#, VB.NET or C++ |
| Where code lives | In the model or external rule files | Compiled add-in installed on each PC |
| User interface | iLogic forms | Ribbon, dialogs, dockable panels |
| Debugging | Basic | Full Visual Studio debugging |
| Version control | Harder for embedded rules | Standard source control |
| Scale | Small to medium rule sets | Large applications and integrations |
| Integration | Limited | Databases, ERP, web services |
When iLogic is the right choice
- Configurable parts and assemblies driven by a few parameters
- Rules owned by the engineering team, who need to change them
- Simple forms for choosing options
- Quick wins such as filling iProperties or suppressing features
When to move to the API
- Rules have grown into thousands of lines copied across many files
- You need a proper user interface or background processing
- You need to connect Inventor to ERP, PLM, databases or web services
- Performance matters on large assemblies
- You need reliable deployment and version control across a team
Start with iLogic for speed. Move to the API when rules become software.
Using both together
Many companies combine the two: iLogic keeps model-level rules close to the design, while an add-in handles the user interface, integration and heavy processing, and calls iLogic rules where useful.
Inventor automation services
See iLogic automation, Inventor API development and Inventor add-in development, and read Inventor automation using the Inventor API.