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Ontonaut
Ontonaut is a modern ontology workbench. Edit OWL 2 ontologies and SKOS vocabularies in plain Turtle files, browse them as a dictionary or a knowledge graph, query with SPARQL, and let AI agents read and edit your ontology over MCP with every change marked and undoable.

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Features
Profile Features Limited 
Languages:
Interface Full Audio Subtitles
English ✔
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About This Software

Ontonaut is a workbench for OWL 2 ontologies and SKOS vocabularies. It reads and writes plain text files that live in your git repository, and it keeps the logic readable in plain English alongside the syntax. If you have used Protégé, think of Ontonaut as the modern take on the same job.

One file, five views

Your ontology stays a plain Turtle file. Ontonaut also opens RDF/XML and JSON-LD, and saves to all four formats.

  • Entities shows everything about a class, property or individual on one page, with inline editing and full undo.

  • Glossary renders SKOS vocabularies as a dictionary, with definitions, synonyms and an A to Z index.

  • Graph draws the knowledge graph. Facts are solid, rules are dashed, and every node is a click away.

  • Query runs SPARQL 1.1 with results that link back into the workbench.

  • Overview tracks metrics, imports, prefixes and reasoner findings.

Readable by design

Every axiom carries its plain English reading next to the logic, so a subclass statement also reads as "Every Woman is also a Person". Reviews go faster, and the domain experts on your team can follow the model without knowing Manchester syntax. When a spec question comes up, the built-in reference pages settle it with the W3C primers' own examples. SKOS integrity rules are checked as you type, so a vocabulary that leaves Ontonaut follows the spec.

Built for AI collaboration

Ontonaut is an MCP server. Connect any MCP client and it can search, query and edit the ontology you have open, live. Every triple an agent writes is stamped with a provenance annotation and wears an AI badge in the interface. Agent edits sit in your undo history like your own.

Honest about the details

The built-in reasoner is structural. It finds unsatisfiable classes, inconsistencies and inferred hierarchies fast, but it is not a complete DL reasoner, so keep HermiT or ELK in your pipeline for full checking. Saving defaults to Turtle because clean diffs matter. Everything runs locally and your files never leave your machine.

System Requirements

    Minimum:
    • Requires a 64-bit processor and operating system
    • OS *: Windows 8.1
    • Processor: Requires a 64-bit processor
    Recommended:
    • Requires a 64-bit processor and operating system
    • OS: Windows 10 or Windows 11
    • Processor: Requires a 64-bit processor
* Starting January 1st, 2024, the Steam Client will only support Windows 10 and later versions.
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