Open Ontologies MCP Server: Setup for Claude, Cursor and Other Apps

• Previews what a change to an ontology would do

  Compares the loaded ontology with proposed Turtle, like a Terraform plan. It reports what is added or removed, how many triples a change touches and a risk score, before anything is applied.

  Try: “Plan this change to the ontology and tell me the blast radius.”

  Read · onto_plan

• Applies a previewed change

  Applies the plan you made earlier, the most recent one unless you name another. Use it after you have read the plan.

  Try: “Apply the plan we just reviewed.”

  Write · onto_apply

• Protects names from being removed

  Locks IRIs so that a plan or apply cannot remove them. Use it for terms other systems depend on.

  Try: “Lock the IRIs for Person and Organisation.”

  Write · onto_lock

• Spots changes between two versions

  Compares two versions of an ontology and reports what drifted between them.

  Try: “Has the ontology drifted since the last release?”

  Read · onto_drift

• Runs watchers that can block changes

  Runs the active monitoring watchers over the ontology. If one trips, applying changes is blocked until you clear it.

  Try: “Run the monitors and tell me if anything is blocked.”

  Read · onto_monitor

• Restores an earlier saved version

  Puts the in-memory ontology back to a version you saved with the snapshot tool.

  Try: “Roll back to the snapshot called before-merge.”

  Write · onto_rollback

• Saves a named snapshot

  Stores a named snapshot of the current ontology so you can return to it later.

  Try: “Save a snapshot called before-merge.”

  Write · onto_version

• Lists saved snapshots

  Shows the saved ontology versions.

  Try: “What snapshots do I have?”

  Read · onto_history

• Loads an ontology from a file or pasted Turtle

  Reads an ontology file, or Turtle text you give it, into the server's working store. Most other tools work on what is loaded.

  Try: “Load pizza.ttl.”

  Files · onto_load

• Checks that ontology syntax is valid

  Checks RDF or OWL syntax in a file or in text and reports parse errors.

  Try: “Validate this Turtle file.”

  Read · onto_validate

• Runs a SPARQL query

  Runs a SPARQL query against the loaded ontology and returns the rows.

  Try: “List every class and its parent.”

  Read · onto_query

• Counts triples, classes and properties

  Reports how many triples, classes, properties and individuals are loaded.

  Try: “Give me stats on the loaded ontology.”

  Read · onto_stats

• Finds quality problems

  Checks the ontology for missing labels, comments, domains and ranges.

  Try: “Lint the ontology and list what is missing.”

  Read · onto_lint

• Compares two ontology files

  Shows which triples were added or removed between two ontology files.

  Try: “What changed between v1.ttl and v2.ttl?”

  Files · onto_diff

• Derives what follows from the ontology

  Runs inference over the loaded ontology and adds the conclusions it can derive. It can also write a certificate that a separate checker can verify.

  Try: “Run the reasoner and write a certificate.”

  Write · onto_reason

• Checks data against SHACL shapes

  Validates the loaded data against SHACL shapes and reports the failures.

  Try: “Check the data against these shapes.”

  Read · onto_shacl

• Tests whether one class is a subclass of another

  Uses description-logic reasoning to answer whether one class is subsumed by another.

  Try: “Is Margherita a kind of Pizza?”

  Read · onto_dl_check

• Explains why a class can never have members

  Gives the reason a class is unsatisfiable under description-logic reasoning.

  Try: “Why is VeganCheesePizza unsatisfiable?”

  Read · onto_dl_explain

• Finds which asserted facts cause a conclusion

  Names the asserted triples responsible for a conclusion or a contradiction.

  Try: “Which facts make this class inconsistent?”

  Read · onto_justify

• Checks that new axioms change nothing old

  Reasons over the base ontology with and without an extension and reports new conclusions about names the base already used.

  Try: “Does adding this module change anything the base said?”

  Read · onto_conservative_check

• Turns a data file into RDF

  Parses CSV, JSON, NDJSON, XML, YAML, XLSX or Parquet into triples and loads them.

  Try: “Load customers.csv as RDF.”

  Write · onto_ingest

• Builds an ontology from one spreadsheet

  Takes one data sheet and produces an OWL class, typed properties, a SHACL shape and a loading mapping, with the evidence for each line.

  Try: “Make an ontology from this spreadsheet.”

  Files · onto_induce

• Loads database rows as RDF

  Runs a SQL query against PostgreSQL or DuckDB and loads the rows as triples. It needs a build with that option, so the standard binaries do not have it.

  Try: “Load this query's rows into the ontology.”

  Network · onto_sql_ingest

• Finds matching terms in two ontologies

  Looks for equivalent or related classes between two ontologies using labels, properties, parents and neighbours.

  Try: “Align these two vocabularies.”

  Read · onto_align

• Fetches an ontology from a URL

  Downloads an ontology from a remote URL or SPARQL endpoint and loads it.

  Try: “Pull the ontology from this URL.”

  Write · onto_pull

• Sends the ontology to a SPARQL endpoint

  Sends the whole current ontology store to a SPARQL endpoint you name, as an INSERT DATA update. The call can carry a username, password or token for that endpoint.

  Try: “Push the current ontology to the staging endpoint.”

  Write · onto_push

• Writes the ontology to a file

  Saves the current ontology store to a file you name.

  Try: “Save the ontology to out.ttl.”

  Write · onto_save

• Empties the loaded ontology

  Clears all triples from the in-memory store. The compile cache file is kept.

  Try: “Clear the loaded ontology.”

  Write · onto_clear

• Deletes a cached ontology copy

  Deletes a named entry from the compile cache. By default it also deletes the compiled N-Triples copy in the cache folder (~/.open-ontologies/cache). The original ontology file you loaded is not touched, and passing delete_file=false keeps the cache file.

  Try: “Remove the pizza ontology from the cache.”

  Delete · onto_cache_remove

• Browses and installs standard ontologies

  Browses the built-in catalogue of 33 standard ontologies and the community pack registry, which it fetches at run time, and installs one.

  Try: “Install the FOAF ontology from the marketplace.”

  Write · onto_marketplace

• Hands the problem to a theorem prover

  Runs a first-order prover, reads the derivation it prints and re-checks what can be re-checked.

  Try: “Prove this with Vampire and check the result.”

  Runs code · onto_fol_prove

• Runs a PDDL planner

  Starts Fast Downward as a separate process on a PDDL domain and problem.

  Try: “Plan these steps with Fast Downward.”

  Runs code · onto_plan_classical

• Runs a tool from an installed plugin

  Calls a tool in an installed WASM plugin. It needs a build with plugins on, so the standard binaries do not have it.

  Try: “Call the plugin's export tool.”

  Runs code · onto_plugin_call

Watch out for

• onto_push sends your ontology to a remote endpoint

  It uploads the full current store as a SPARQL INSERT DATA update to any endpoint URL in the call, and the call can carry a username, password or token for it. It adds data and does not drop graphs. Check the address before you approve it. github.com

• Some tools write files and delete cached copies

  onto_save, onto_pack and conversion tools write files you name. onto_cache_remove (and onto_unload with delete_cache) deletes the compiled N-Triples copy in ~/.open-ontologies/cache by default. It does not delete the source file you loaded, and reloading rebuilds the cache. Approve each call that names a path. github.com

• Some tools start other programs

  The planner tool starts Fast Downward and the prover tool runs a first-order prover. Both need those programs installed. github.com

• The tool list is very large

  The default profile exposes every tool. Use --tool-profile with a job name such as validation or authoring to expose fewer. github.com

Security advisories