orionbelt-ontology-builder

Browser ontology workbench for OWL and SKOS on Streamlit + rdflib: OWL-RL reasoning, 22 SKOS checks, SPARQL console, bulk edits, gist starters and a vis-network graph — no Java, no Protégé.

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Curator's take

For the ontology work that a knowledge-graph project actually needs — classes, properties, SKOS vocabularies, cleanup — without installing Protégé: pip install, open the browser, and every change is an undo checkpoint, every delete shows what breaks first, every import shows a diff. Validation names the orphan classes, duplicate labels and broader/narrower cycles with locations. Human-first, deliberately lighter than Protégé. NOT an agent-facing tool (no MCP, no API — Streamlit is the interface), NOT for pure RDFS vocabularies like schema.org (they don't surface in the panels), and the licence is unspecified — check before you build on it.

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README.md1 min read

OrionBelt Logo

OrionBelt Ontology Builder

A browser-based ontology workbench built with Streamlit and rdflib

Build and explore OWL ontologies directly in your browser.

✔ Visual graph editor
✔ OWL RL reasoning & consistency checks
✔ OWL + SKOS in one workbench
✔ SKOS mappings, poly-hierarchy, 22 checks
✔ Read-only SPARQL console
✔ RDF/OWL import & export
✔ Pure Python: hosted app, browser or desktop

Try it now: orionbelt.streamlit.app

OrionBelt Ontology Builder Screenshot

What is this?

OrionBelt lets you build, edit, and maintain OWL ontologies and SKOS vocabularies in your browser. No Java, no desktop install - just pip install and go.

It works with OWL ontologies (classes as owl:Class, properties as owl:ObjectProperty / owl:DatatypeProperty). Pure RDFS vocabularies like schema.org that use rdfs:Class and rdf:Property are not currently surfaced in the Classes / Properties panels.

It's not trying to be Protégé. It's meant for people who want something lighter: a workbench that's easy to pick up, hard to break things with, and good enough for real ontology work.

What it's good at

Not losing your work. Every change creates an undo checkpoint. Deletes show you what will break before you confirm. Imports show a diff so you can review before applying.

Keeping your ontology clean. Validation catches orphan classes, duplicate labels, domain/range mismatches, missing annotations, and SKOS-specific issues like broader/narrower cycles. Not just "you have warnings" but "here's what's wrong and where."

Moving fast in large ontologies. Global search across everything. Usage/backlink views for any resource. Click a node in the