OntoLive
Every ontology tool needs a Java install. This one needs a browser tab.
OntoLive is an OWL ontology viewer that runs entirely in the browser. Drop in a .owl (RDF/XML) or .ttl (Turtle) file and browse its class hierarchy as a live diagram. Click a class to centre on it, then drag the depth slider: the diagram redraws on every step of the slider, even for a hundred-class neighbourhood.
It also has a second mode. A small language model running on your GPU reads a paragraph and writes an ontology one line at a time, and the diagram grows with every token. Guardrails check each partial answer and turn a class red when the model puts it in a subclass cycle, makes it its own parent, or invents a near-duplicate.
Live demo: https://vishalmysore.github.io/ontolive/
Why it is fast enough to be live
The diagrams are Mermaid classDiagram text drawn by Pele, a synchronous Mermaid renderer with no dependencies. Because Pele returns SVG in a few milliseconds, the page can redraw on every slider tick and on every streamed token. A toggle switches the same text to Mermaid.js so you can see the difference, and the Race button times both renderers on the current view, in your browser. On a 59-class Pizza neighbourhood we measured a median of 1.2 ms for Pele and 476 ms for Mermaid.js. Measure it on your own machine; numbers vary by hardware.
Mapping OWL to a class diagram
| OWL | Drawn as |
|---|
rdfs:subClassOf a named class | inheritance arrow |
named conjunct of an owl:equivalentClass definition | inheritance arrow, dashed box (a defined class) |
object property domain → range | association, labelled with the property |
someValuesFrom / allValuesFrom / hasValue restriction | dashed dependency (toggle "Restrictions") |
datatype property with a domain | attribute inside the class box |
| cardinalities, unions, complements, disjointness | listed in the side panel in Manchester syntax |
A class diagram cannot express every OWL axiom, so the side panel shows them as text, the way Protégé does.
Features
- RDF/XML (including internal DTD entities such as
&owl;), Turtle, N-Triples. Files are read locally and never uploaded.
- Overview mode (levels below the roots) and focus mode (hops out from a class along every visible edge).
- Searchable class list, details panel, shareable links (
#src=pizza&focus=Margherita&depth=2).
- Sweep depth animates the slider for screen recordings; Download SVG keeps the current theme.
- Colours come from CSS variables, so the diagram follows light and dark mode without being re-rendered.
- LLM mode: WebLLM (Qwen2.5, Llama 3.2, Phi-3.5; q4f32 builds first), streaming extraction, guardrails, export to Turtle or open the result in the explorer.
Run it
npm install
npm run dev
npm test
The tests parse the bundled Turtle sample and, when tests/fixtures/pizza.owl exists, the canonical Pizza ontology. Fetch it from owlcs/pizza-ontology. The site loads Pizza from that repository at runtime; it is not redistributed here.
Credits
Pele by Obsidian, N3.js, WebLLM, Mermaid for the comparison, and the Pizza ontology from the University of Manchester.
License
MIT
