Onto MCP Server

FastMCP server for Onto platform access via a configured Onto API key.

Runtime Contract

Required environment variables:

• ONTO_API_BASE
• ONTO_API_KEY

Optional environment variables:

• ONTO_API_KEY_HEADER default: X-API-Key
• ONTO_API_KEY_PASSTHROUGH_HEADER default: X-Onto-Api-Key
• MCP_TRANSPORT values: stdio, http
• PORT
• SESSION_STATE_API_BASE
• SESSION_STATE_API_KEY

The server no longer supports login/password, OAuth code exchange, or manual user token flows.

In HTTP mode, Onto backend authentication can come from either:

• server-side ONTO_API_KEY
• incoming request header X-Onto-Api-Key (or the value of ONTO_API_KEY_PASSTHROUGH_HEADER)

SESSION_STATE_API_KEY remains optional unless you use the session-state helper tools.

Tools

• list_available_realms()
• about_onto(focus="")
• search_templates(name_part, realm_id=None, include_children=False, include_parents=False)
• search_relation_templates(realm_id, relation_type_name="", meta_ids=None)
• search_entities_by_relations(realm_id, searched_meta_ids, predicates=None, include_descendants=True, first=0, offset=100, sort=None)
• search_objects(realm_id=None, name_filter="", template_uuid="", comment_filter="", load_all=False, page_size=20)
• create_realm(name, comment="")
• update_realm(realm_id, name, comment="")
• delete_realm(realm_id)
• save_template(realm_id, name, comment="", template_id="")
• create_template(realm_id, name, comment="")
• get_template(realm_id, template_id, include_children=False, include_parents=False, name="")
• delete_template(realm_id, template_id)
• link_template_to_parents(realm_id, child_template_id, parent_template_ids)
• unlink_template_from_parents(realm_id, child_template_id, parent_template_ids)
• save_entity(realm_id, name, comment="", entity_id="", meta_entity_id="")
• save_entities_batch(realm_id, entities)
• create_entities_batch(realm_id, entities)
• get_entity(realm_id, entity_id, related_diagrams=False, related_entities=False, with_empty_stickers=False, name="")
• get_node_chat_messages(realm_id, node_id)
• create_node_chat_message(realm_id, node_id, text)
• search_entities(realm_id=None, name_filter="", meta_entity_id="", comment_filter="", include_inherited=False, offset=0, limit=20)
• search_entities_with_related_meta(realm_id=None, name_filter="", meta_entity_id="", comment_filter="", include_inherited=False, offset=0, limit=20)
• delete_entity(realm_id, entity_ids, name="")
• save_entity_fields(realm_id, entity_id, fields)
• delete_entity_fields(realm_id, entity_id, field_ids)
• save_template_fields(realm_id, template_id, fields)
• delete_template_fields(realm_id, template_id, field_ids)
• search_diagrams(realm_id, name_part="", tag_ids=None, page=1, size=20)
• search_context_tags(realm_id, name_part="", page=1, size=20)
• create_context_tag_from_object(realm_id, entity_id)
• add_diagram_tag(realm_id, diagram_id, tag_id)
• remove_diagram_tag(realm_id, diagram_id, tag_id)
• add_existing_nodes_to_diagram(realm_id, diagram_id, nodes)
• create_diagram(realm_id, name, comment="")
• get_diagram(realm_id, diagram_id)
• update_diagram(realm_id, diagram_id, name="", comment="", tag_ids=None)
• delete_diagram(realm_id, diagram_id)
• create_relation(realm_id, start_entity_id, end_entity_id, relation_type_name, start_role="", end_role="", additional_properties=None)
• update_relation(realm_id, start_entity_id, end_entity_id, relation_type_name, start_role="", end_role="", additional_properties=None)
• delete_relation(realm_id, start_entity_id, end_entity_id, relation_type_name, name="")
• create_meta_relation(realm_id, start_meta_id, end_meta_id, relation_type_name, start_min=0, start_max=1, end_min=0, end_max=1, equal=False)
• update_meta_relation(realm_id, start_meta_id, end_meta_id, relation_type_name, start_min=0, start_max=1, end_min=0, end_max=1, equal=False)
• delete_meta_relation(realm_id, start_meta_id, end_meta_id, relation_type_name)
• saveOntoAIThreadID(thread_external_id, ctx)
• getOntoAIThreadID(ctx)

Resources

• onto://spaces
• onto://user/info

Configuration Example

{
  "mcpServers": {
    "onto-mcp-server": {
      "command": "python",
      "args": ["-m", "onto_mcp.server"],
      "cwd": "/path/to/repo",
      "env": {
        "ONTO_API_BASE": "https://app.ontonet.ru/api/v2/core",
        "ONTO_API_KEY": "replace-with-onto-api-key"
      }
    }
  }
}

Running

python -m pip install -r requirements.txt
python -m onto_mcp.server

HTTP mode:

MCP_TRANSPORT=http PORT=8080 python -m onto_mcp.server

If you use HTTP mode or session-state helpers, also configure SESSION_STATE_API_KEY.