A thin MCP server that delegates all business logic to the OrionBelt® Semantic Layer REST API via HTTP. No embedded engine — pure API pass-through.
Architecture
The OrionBelt® Semantic Layer platform has two deployment modes. This MCP server supports both:
- Standalone — Deploy the OrionBelt® Semantic Layer API anywhere (Cloud Run, Docker, localhost) and point this MCP server at it via
API_BASE_URL.
- Hosted — Connect to the public Cloud Run deployment with zero local setup (see Hosted MCP Server below).
┌────────────┐ ┌──────────────────────────────────────────────────────┐
│ LLM Client │ │ OrionBelt® Platform │
│ │ │ │
│ Claude, │──MCP──│──> server.py ──HTTP /v1──> Semantic Layer REST API │
│ Cursor, │ │ (FastMCP (FastAPI: parse OBML, │
│ any MCP │ │ + httpx) validate, compile │
│ client │ │ to SQL) │
└────────────┘ └──────────────────────────────────────────────────────┘
- No business logic — all tool calls delegate to the REST API (v1 endpoints)
- Dual-mode — auto-detects single-model or multi-model API mode at startup
- Auto-session management — creates an API session on first tool call, caches the ID (multi-model mode)
- 27 tools (single-model mode) or 31 tools (multi-model mode) for querying (QueryObject), execution, batch, discovery, dimension-value search, composability (ACR), examples, diagrams, RDF/SPARQL, lineage of artefacts and queries, business rules (list, explain, evaluate), ontology links (concept mappings, namespaces, unmapped artefacts), OSI export, model validation (offline or against the live datasource), and OBML reference + function catalog + JSON schemas + configured data sources. (32 distinct tools exist in total; the API mode selects which subset is active — they overlap in 26 — and no client ever sees all 32 at once.) The visible surface is narrowed further in the design-time phase and when query execution is disabled (see Design-time vs run-time tool switching)
- 5 prompts + 2 resources for OBML / OBSQL reference, business rules, and usage guidance
Live Demo
A public demo of the OrionBelt® Semantic Layer API is available at:
API endpoint: https://orionbelt.ralforion.com — Swagger UI | ReDoc | Gradio UI
Set API_BASE_URL=https://orionbelt.ralforion.com in your .env file to use it (see .env.example).
Installation
uv sync
For development (includes pytest, respx, ruff):
uv sync --all-groups
Usage
stdio (default)
uv run server.py
HTTP transport
MCP_TRANSPORT=http uv run python server.py
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