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owl-mcp

mcp
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SUMMARY

MCP server for modifying OWL files written in Rust

README.md

OWL MCP

npm version
CI
License: MIT
Rust
Node

A high-performance Model Context Protocol (MCP) server and CLI for OWL ontology management, written in Rust.

Built as a drop-in replacement for ai4curation/owl-mcp, designed to eliminate the crashes and timeouts inherent to the Python implementation. Axioms are expressed in OWL Functional Syntax.

Features

  • 12 MCP tools — add, remove, search, and inspect axioms; manage prefixes, labels, and ontology IRIs; scan for modeling pitfalls; evaluate ontology quality; run SPARQL queries
  • CLI mode — every tool is also available as a direct CLI subcommand (owl-mcp find-axioms ...)
  • 2 transport modes — stdio (default, for Cursor/Claude Desktop) and http (Streamable HTTP + SSE)
  • Live file watching — automatically reloads ontology files modified externally
  • OFN and RDF/XML support — reads and writes both formats; format is auto-detected from file extension and content
  • Never crashes — errors are returned as MCP tool failures, not panics

Installation

via npx (recommended)

npx owl-mcp serve

via npm (global install)

npm install -g owl-mcp
owl-mcp --help

Build from source

Requires Rust 1.75+.

git clone https://github.com/Minitour/owl-mcp
cd owl-mcp
cargo build --release
./target/release/owl-mcp --help

Usage

owl-mcp has two modes: serve (MCP server) and CLI (direct commands).

MCP server mode

owl-mcp serve [OPTIONS]

Options:
  --transport <stdio|http>   Transport to use [default: stdio]
  --host <HOST>              Host to bind (HTTP only) [default: 127.0.0.1]
  --port <PORT>              Port to bind (HTTP only) [default: 8080]
  --sse-support              Enable legacy SSE endpoint [default: true]

CLI mode

Every MCP tool is available as a subcommand:

owl-mcp add-axiom --file ontology.owl --axiom "SubClassOf(:Dog :Animal)"
owl-mcp find-axioms --file ontology.owl --pattern "Dog" --limit 50
owl-mcp get-all-axioms --file ontology.owl --include-labels
owl-mcp test-pitfalls --file ontology.owl
owl-mcp test-quality --file ontology.owl
owl-mcp sparql --file ontology.owl --query "SELECT ?c WHERE { ?c a owl:Class }"
owl-mcp sparql --file schema.owl --file data.owl --query "ASK { ?i a :Plan }"

Run owl-mcp --help for a full list of commands, or owl-mcp <command> --help for details on a specific command.

Cursor / Claude Desktop integration

Add the server to your MCP client configuration.

Cursor (~/.cursor/mcp.json or .cursor/mcp.json in your project):

{
  "mcpServers": {
    "owl-mcp": {
      "command": "npx",
      "args": ["-y", "owl-mcp", "serve"]
    }
  }
}

HTTP transport (useful for remote/shared setups):

{
  "mcpServers": {
    "owl-mcp": {
      "url": "http://localhost:8080/mcp"
    }
  }
}

Start the server with:

owl-mcp serve --transport http --port 8080

Tools

All tools operate on OWL files by absolute path. The manager lazily loads files on first access and caches them for subsequent calls.

Axiom operations

Tool Description
add_axiom Add a single axiom in OWL Functional Syntax
add_axioms Add multiple axioms in one call
remove_axiom Remove an axiom
find_axioms Search axioms with a regex pattern
get_all_axioms List all axioms (up to a limit)

Metadata and labels

Tool Description
add_prefix Add a prefix mapping (ex: → http://example.org/)
ontology_metadata Return ontology-level annotation axioms
get_labels_for_iri Look up rdfs:label (or custom property) values for an IRI
set_ontology_iri Set or update the ontology IRI and version IRI

Quality checks

Tool Description
test_pitfalls Scan for 31 common modeling pitfalls (inspired by OOPS!)
test_quality Evaluate ontology quality using the OQuaRE framework (ISO/IEC 25000 SQuaRE)

find_axioms and get_all_axioms accept include_labels: true to annotate each axiom with human-readable labels appended as ## <IRI> # label comments.

test_quality uses the whelk OWL EL reasoner to compute inferred class hierarchy and returns a JSON report containing 19 raw and scaled metrics (ANOnto, AROnto, CBOOnto, CROnto, DITOnto, INROnto, LCOMOnto, NACOnto, NOCOnto, NOMOnto, RFCOnto, RROnto, TMOnto, WMCOnto, and variants), 22 subcharacteristics, 7 quality characteristics (Structural, Functional Adequacy, Maintainability, Operability, Reliability, Transferability, Compatibility), and an overall OQuaRE score on a 1–5 scale.

Querying

Tool Description
sparql_query Run a SPARQL query over one or more OWL files

sparql_query takes owl_file_paths (one or more absolute paths) and a query string. Each file is serialized to RDF and loaded together into an in-memory oxigraph store, so passing several paths merges a schema with its ABox or imports before the query runs. SELECT and ASK return the standard SPARQL 1.1 JSON results format; CONSTRUCT and DESCRIBE return a list of N-Triples. Queries run over asserted triples (no reasoning is applied).

Development

# Run tests
cargo test

# Check formatting and lints
cargo fmt --check
cargo clippy --all-targets -- -D warnings

# Build release binary
cargo build --release

License

MIT

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