OWL MCP

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

• 11 MCP tools — add, remove, search, and inspect axioms; manage prefixes, labels, and ontology IRIs; scan for modeling pitfalls; evaluate ontology quality
• 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

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.

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