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