Navigation: OWL ontology checker · OWL ontology publishing guide · API docs

Ask Wol Beta OWL Ontology Checker & Reviewer

Your friendly owl (Wollie, to friends) for free online OWL ontology checks during modelling and before publication. Enter a URL or upload a file to get a class diagram and a review report.

Preparing to publish? Follow the OWL ontology publishing guide.

Ontology URL

Examples

Ontology file

Accepts Turtle, RDF/XML, JSON-LD, N-Triples, or N3.

Advanced options

RDF format Base IRI for relative identifiers

If your file uses relative identifiers, supply its intended base IRI or declare @base (Turtle) or xml:base (RDF/XML) in the file. This setting does not download a URL. Learn more.

What do you get?

An interactive class diagram and an HTML report (or JSON via the API). The checks below link to the relevant sections of the publishing guide.

1. Ontology basics

1.1 Ontology metadata: SHACL validation of the ontology header against Ask Wol's built-in shapes: title, description, creator, and version are the core properties; created and modified dates and publisher are additional. Every missing property is reported as a recommendation.
1.2 Imports: fetches directly declared owl:imports targets and checks that they provide parseable RDF. Nested imports are not followed.
1.3 IRI strategy: the ontology's own defined terms should consistently use either hash (#Term) or slash (/Term), not both.
1.4 IRI scheme: each namespace (the base IRI, not just the host) should be referenced under a single URI scheme. http://example.org/X and https://example.org/X are different IRIs.
1.5 Open licence: checks ontology-header dcterms:license or schema:license values against known licences. Missing, unrecognised, non-open, non-preferred or multiple licences are recommendations; CC0 and CC BY are preferred.

2. Namespaces & reuse

2.1 Namespaces: fetches namespaces with subject-position terms, checks HTTP status, and tries to parse RDF (Turtle, RDF/XML, JSON-LD, N-Triples). Falls back to scanning HTML pages for RDF links.
2.2 Unused prefixes: flags detected prefix bindings whose namespace has no matching IRI use, including header and literal datatype IRIs.
2.3 External term definitions: checks whether external subject IRIs occur in the retrieved vocabulary RDF. Terms not found there and upstream deprecation are warnings. Predicate-only and object-only references are excluded.

3. Term structure

3.1 Internal term definitions: flags terms in the ontology's own namespace that are referenced but never defined. Usually a typo or a forgotten declaration.
3.2 Term inventory & naming: categorises every internal term and checks capitalisation: classes start uppercase, properties lowercase. Coded identifiers are exempt.
3.3 Domains & ranges: checks directly declared domains and ranges of internal object and datatype properties. Missing declarations are recommendations; selected named class/datatype mismatches are errors. Anonymous expressions are not evaluated.
3.4 Datatypes: Checks datatype IRIs against recognised built-ins and local declarations. Literal values and OWL profile conformance are not validated.
3.5 Non-ontology terms: lists internal skos:Concept instances with a TDCC recommendation to consider separate management of concept schemes. This is an organisation preference, not an OWL validity requirement.

4. Term documentation

4.1 Labels: a SHACL check for missing rdfs:label values on internal classes and properties. Deprecated terms are exempt.
4.2 Comments: a SHACL check for missing rdfs:comment values on internal classes and properties. Comments on inverse properties count; deprecated terms are exempt.
4.3 Language tag consistency: labels and definitions (rdfs:label, rdfs:comment, skos:prefLabel, skos:definition, ...) on internally defined terms should use language tags consistently.

5. Logic

5.1 Reasoner checks: Selected OWL RL/RDF checks for contradictory class memberships of named individuals and unsatisfiable internal classes in the current document; imports excluded. Passing these checks does not establish consistency or OWL 2 DL conformance.

Automatic checks cannot assess whether your ontology faithfully models its intended domain.

Other resources

Protégé: a free, open-source ontology editor.
The Pizza Tutorial: a revised Protégé 5 version of the classic hands-on OWL tutorial.
Linked Open Vocabularies (LOV): a catalogue of reusable RDF vocabularies.
OntoChoice: an initiative on choosing ontologies and terms.
OOPS!: an online scanner for common ontology pitfalls.
FOOPS!: an online tool for assessing the FAIRness of ontologies and vocabularies.
ROBOT: a command-line tool for automating ontology engineering workflows.

Why “askwol”?

The W3C working group used the name WOL during OWL’s development. Tim Finin proposed rearranging it to OWL because “owls are associated with wisdom.” In Milne’s Winnie-the-Pooh, Owl spells his own name WOL, as Dave de Roure pointed out to the working group.

About

askwol is developed and maintained by the TDCC-NES Ontology Engineers (Kathrin Füllenbach and Dani Metilli), funded by Open Science NL. We help with ontology selection and reuse, co-development, knowledge graph design, and training.

askwol is free and open source under the MIT licence. It is currently in beta: some checks may be incomplete or produce false positives. Found a bug or have an idea? Open an issue on GitHub or reach us at nes@tdcc.nl.