OpenCrab

MetaOntology OS MCP Server Plugin

Carcinization is the evolutionary tendency for crustaceans to converge on a crab-like body plan.OpenCrab applies the same principle to agent environments:all sufficiently advanced AI systems eventually evolve toward ontology-structured forms.

OpenCrab is an MCP (Model Context Protocol) server that exposes the MetaOntology OS grammarto any OpenClaw-compatible agent environment — Claude Code, n8n, LangGraph, and beyond.

Architecture

                        ┌─────────────────────────────────────────────┐
                        │           OpenCrab MCP Server               │
                        │              (stdio JSON-RPC)               │
                        └──────────────────┬──────────────────────────┘
                                           │
              ┌────────────────────────────┼────────────────────────────┐
              │                           │                            │
      ┌───────▼──────┐           ┌────────▼───────┐          ┌────────▼───────┐
      │  grammar/    │           │   ontology/    │          │    stores/     │
      │  manifest.py │           │   builder.py   │          │                │
      │  validator.py│           │   rebac.py     │          │  neo4j_store   │
      │  glossary.py │           │   impact.py    │          │  chroma_store  │
      └──────────────┘           │   query.py     │          │  mongo_store   │
                                 └────────────────┘          │  sql_store     │
                                                             └───────┬────────┘
                                                                     │
                              ┌──────────────────────────────────────┤
                              │              Data Layer              │
              ┌───────────────┼───────────────┬──────────────────────┤
              │               │               │                      │
      ┌───────▼──────┐ ┌──────▼──────┐ ┌─────▼──────┐ ┌────────────▼───┐
      │    Neo4j     │ │  ChromaDB   │ │  MongoDB   │ │  PostgreSQL    │
      │  (graph)     │ │  (vectors)  │ │ (documents)│ │  (registry +   │
      │  Cypher      │ │  semantic   │ │  audit log │ │   ReBAC policy)│
      │  traversal   │ │  search     │ │            │ │                │
      └──────────────┘ └─────────────┘ └────────────┘ └────────────────┘

MetaOntology OS — 9 Spaces

Space	Node Types	Role
subject	User, Team, Org, Agent	Actors with identity and agency
resource	Project, Document, File, Dataset, Tool, API	Artifacts that subjects act upon
evidence	TextUnit, LogEntry, Evidence	Raw empirical observations
concept	Entity, Concept, Topic, Class	Abstract knowledge
claim	Claim, Covariate	Derived assertions
community	Community, CommunityReport	Concept clusters
outcome	Outcome, KPI, Risk	Measurable results
lever	Lever	Tunable control variables
policy	Policy, Sensitivity, ApprovalRule	Governance rules

MetaEdge Relationship Grammar

subject    ──[owns, manages, can_view, can_edit, can_execute, can_approve]──► resource
resource   ──[contains, derived_from, logged_as]──────────────────────────► evidence
evidence   ──[mentions, describes, exemplifies]────────────────────────────► concept
evidence   ──[supports, contradicts, timestamps]───────────────────────────► claim
concept    ──[related_to, subclass_of, part_of, influences, depends_on]────► concept
concept    ──[contributes_to, constrains, predicts, degrades]──────────────► outcome
lever      ──[raises, lowers, stabilizes, optimizes]───────────────────────► outcome
lever      ──[affects]─────────────────────────────────────────────────────► concept
community  ──[clusters, summarizes]────────────────────────────────────────► concept
policy     ──[protects, classifies, restricts]─────────────────────────────► resource
policy     ──[permits, denies, requires_approval]──────────────────────────► subject

Quick Start

1. Start the data services

docker-compose up -d

This starts Neo4j, MongoDB, PostgreSQL, and ChromaDB.

2. Install OpenCrab

pip install -e ".[dev]"

3. Configure environment

opencrab init          # creates .env from template
# Edit .env if your credentials differ from defaults

4. Seed example data

python scripts/seed_ontology.py

5. Verify connectivity

opencrab status

6. Add to Claude Code MCP

claude mcp add opencrab -- opencrab serve

Or add to your .claude/mcp.json manually (see below).

7. Run a query

opencrab query "system performance and error rates"
opencrab manifest    # see the full grammar

Claude Code MCP Configuration

Add to ~/.claude/mcp.json (or project-level .mcp.json):

{
  "mcpServers": {
    "opencrab": {
      "command": "opencrab",
      "args": ["serve"],
      "env": {
        "NEO4J_URI": "bolt://localhost:7687",
        "NEO4J_USER": "neo4j",
        "NEO4J_PASSWORD": "opencrab",
        "MONGODB_URI": "mongodb://root:opencrab@localhost:27017",
        "MONGODB_DB": "opencrab",
        "POSTGRES_URL": "postgresql://opencrab:opencrab@localhost:5432/opencrab",
        "CHROMA_HOST": "localhost",
        "CHROMA_PORT": "8000"
      }
    }
  }
}

Alternatively, with uvx (no install required):

{
  "mcpServers": {
    "opencrab": {
      "command": "uvx",
      "args": ["--from", "opencrab", "opencrab", "serve"]
    }
  }
}

MCP Tool Reference

`ontology_manifest`

Returns the full MetaOntology grammar: spaces, meta-edges, impact categories,active metadata layers, and ReBAC configuration.

{}

`ontology_add_node`

Add or update a node in the ontology.

{
  "space": "subject",
  "node_type": "User",
  "node_id": "user-alice",
  "properties": {
    "name": "Alice Chen",
    "role": "analyst"
  }
}

`ontology_add_edge`

Add a directed edge (grammar-validated before write).

{
  "from_space": "subject",
  "from_id": "user-alice",
  "relation": "owns",
  "to_space": "resource",
  "to_id": "doc-spec"
}

Returns a validation error if the relation is not valid for the given space pair.

`ontology_query`

Hybrid vector + graph search.

{
  "question": "What factors degrade system performance?",
  "spaces": ["concept", "outcome"],
  "limit": 10
}

`ontology_impact`

Impact analysis: which I1–I7 categories are triggered by a change?

{
  "node_id": "lever-cache-ttl",
  "change_type": "update"
}

Returns triggered impact categories, affected neighbouring nodes, and a summary.

`ontology_rebac_check`

Relationship-based access control check.

{
  "subject_id": "user-alice",
  "permission": "edit",
  "resource_id": "ds-events"
}

Returns { "granted": true/false, "reason": "...", "path": [...] }.

`ontology_lever_simulate`

Predict downstream outcome changes from a lever movement.

{
  "lever_id": "lever-cache-ttl",
  "direction": "lowers",
  "magnitude": 0.7
}

`ontology_ingest`

Ingest text into the vector and document stores.

{
  "text": "The Q4 incident report shows error rates increased by 40%...",
  "source_id": "incident-2026-01",
  "metadata": {
    "space": "evidence",
    "type": "incident_report"
  }
}

CLI Reference

opencrab init              Create .env from template
opencrab serve             Start MCP server (stdio)
opencrab status            Check store connections
opencrab ingest <path>     Ingest files into vector store
opencrab query <question>  Run a hybrid query
opencrab manifest          Print MetaOntology grammar

Global flags:

opencrab --version         Show version
opencrab query --json-output <q>   Raw JSON output
opencrab manifest --json-output    Raw JSON grammar
opencrab ingest -r <dir>   Recursive ingestion
opencrab ingest -e .txt,.md <dir>  Filter by extension

Impact Categories (I1–I7)

ID	Name	Question
I1	Data impact	What data values or records change?
I2	Relation impact	What graph edges are affected?
I3	Space impact	Which ontology spaces are touched?
I4	Permission impact	Which access permissions change?
I5	Logic impact	Which business rules are invalidated?
I6	Cache/index impact	Which caches or indexes must be refreshed?
I7	Downstream system impact	Which external systems or APIs are affected?

Active Metadata Layers

Every node and edge can carry orthogonal metadata attributes:

Layer	Attributes
existence	identity, provenance, lineage
quality	confidence, freshness, completeness
relational	dependency, sensitivity, maturity
behavioral	usage, mutation, effect

Development

make dev-install    # install with dev extras
make up             # start docker services
make seed           # seed example data
make test           # run test suite
make coverage       # test + coverage report
make lint           # ruff linter
make format         # black + isort
make status         # check store connections

Running integration tests

Integration tests require live services:

OPENCRAB_INTEGRATION=1 pytest tests/ -v

Project structure

opencrab/
├── grammar/          # MetaOntology grammar (manifest, validator, glossary)
├── stores/           # Store adapters (Neo4j, ChromaDB, MongoDB, PostgreSQL)
├── ontology/         # Ontology engine (builder, ReBAC, impact, query)
└── mcp/              # MCP server (stdio JSON-RPC) and tool definitions
tests/                # Test suite (grammar, stores, MCP tools)
scripts/              # Seed script
docker-compose.yml    # All data services

License

MIT — see LICENSE.

OpenCrab: resistance is futile. Your agent will become an ontology.