Quiddity is a knowledge engineering tool that leverages IDEF5 for creating and modeling ontologies. I've been working with ontologies for many years and I always wanted a tool that could create models that used IDEF5. I created a Visio stencil back in 2018, but I always wanted something lightweight that ran in the browser. Ergo, Quiddity was born.

There are two ways you can access Quiddity:

• Try the hosted version in desktop browsers and iOS
• Clone the repo and load up index.html in your browser

The ✦ AI button opens an AI assistant powered by Claude — describe what you want to model in plain English and it builds the diagram directly on the canvas. Bring your own Anthropic API key; it's stored in your browser and never sent to a server.

Documentation for how to use Quiddity is in the Help menu on the toolbar.

There are some example ontologies in the Examples submenu under Help.

In philosophy, quiddity is "the inherent nature or essence of someone or something." It refers to the essence of an object, describing properties that the thing shares with others of its kind. You can define, and discover, what makes something what it is through ontology.

If you are unfamiliar with IDEF5, learn more about it and be sure to check out the other Integrated DEFinition Methods while you're there.

Issues and contributions are always welcome!