🇨🇭 Part of the Swiss Public Data MCP Portfolio

⚖️ openlex-mcp

MCP Server for Canton Zurich legislation (ZH-Lex) — full-text search, article extraction, and education law tools for ~970 cantonal laws

🇩🇪 Deutsche Version

Overview

openlex-mcp provides AI-native access to the entire legal collection of Canton Zurich (Zürcher Gesetzessammlung). It combines full-text data from HuggingFace with live metadata from the official zh.ch website, storing everything in a local SQLite database with FTS5 full-text indexing for sub-50ms search performance.

Built for the Schulamt (school department) of the City of Zurich, but covers all areas of cantonal law — from tax law to building regulations.

Anchor demo query: "What does the Volksschulgesetz say about parental involvement? Show me Art. 55 VSG and find all articles that mention 'Elternrat'."

Features

• ⚖️ 8 tools covering search, retrieval, article extraction, and cache management
• 🔍 FTS5 full-text search across ~970 cantonal laws with BM25 ranking
• 📑 Article extraction — parse individual articles (Art. / §) with paragraph detection
• 🏫 Education law shortcuts — specialized search for LS 412.x series (Volksschulgesetz, Lehrpersonalverordnung, etc.)
• 🌐 Live metadata from zh.ch for current validity status and PDF links
• 💾 Hybrid architecture — cached full-text (HuggingFace) + live metadata (zh.ch)
• 🔓 No API key required — all data under open licenses (CC-BY-SA 4.0)
• ☁️ Dual transport — stdio (Claude Desktop) + Streamable HTTP (cloud)

Development Phase

Current phase: Phase 1 — Read-Only. All tools are read-only (readOnlyHint: true); no writes to external systems. See ROADMAP.md for the phase plan and transition gates before any write or multi-agent capability is added.

Prerequisites

• Python 3.11+
• uv (recommended) or pip
• Internet connection (for initial data download and live metadata)

Installation

# Clone the repository
git clone https://github.com/malkreide/openlex-mcp.git
cd openlex-mcp

# Install
pip install -e .
# or with uv:
uv pip install -e .

Quickstart

# stdio (for Claude Desktop)
python -m openlex_mcp.server

# Streamable HTTP — binds to 127.0.0.1:8000 by default (localhost only)
python -m openlex_mcp.server --http --port 8000

Network binding

By default the HTTP transport binds to 127.0.0.1 (localhost only). The host and port are configurable via the MCP_HOST / MCP_PORT environment variables (or the --host / --port CLI flags, which take precedence).

Never bind to 0.0.0.0 outside a container — it exposes the server to your local network (NeighborJack risk). For containerized/cloud deployments set MCP_HOST=0.0.0.0 explicitly; when that happens outside a detected container the server logs a warning.

Try it immediately in Claude Desktop:

"What is the Volksschulgesetz (VSG)?" "Find all Zurich laws about data protection" "Show me Art. 1 of the Volksschulgesetz" "Which education laws mention 'Schulleitung'?"

Configuration

Claude Desktop

Edit ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):

{
  "mcpServers": {
    "openlex": {
      "command": "python",
      "args": ["-m", "openlex_mcp.server"]
    }
  }
}

Or with the installed entry point:

{
  "mcpServers": {
    "openlex": {
      "command": "openlex-mcp"
    }
  }
}

Config file locations:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

Cloud Deployment (SSE for browser access)

For use via claude.ai in the browser (e.g. on managed workstations without local software):

Render.com (recommended):

1. Push/fork the repository to GitHub
2. On render.com: New Web Service → connect GitHub repo
3. Set start command: python -m openlex_mcp.server --http --port 8000
4. Set environment variable MCP_HOST=0.0.0.0 so the container is reachable (the code default is 127.0.0.1; Render sets the RENDER env var, so no NeighborJack warning is logged)
5. Set MCP_CORS_ORIGINS=https://claude.ai so the browser can read the Mcp-Session-Id header (comma-separated list; no wildcard — defaults to empty, i.e. no cross-origin access)
6. In claude.ai under Settings → MCP Servers, add: https://your-app.onrender.com/sse

💡 "stdio for the developer laptop, SSE for the browser."

Available Tools

Search & Browse

Article Extraction

Metadata & Cache

Key Legal Area Prefixes (LS Numbers)

Example Use Cases

Architecture

┌─────────────────┐     ┌──────────────────────────────┐     ┌──────────────────────────┐
│   Claude / AI   │────▶│  OpenLex MCP                 │────▶│  HuggingFace             │
│   (MCP Host)    │◀────│  (MCP Server)                │◀────│  rcds/swiss_legislation   │
└─────────────────┘     │                              │     │  (974 ZH laws, cached)   │
                        │  8 Tools                     │     ├──────────────────────────┤
                        │  SQLite + FTS5 Cache         │────▶│  zh.ch ZH-Lex            │
                        │  Stdio | HTTP                │◀────│  (live metadata + PDFs)  │
                        │                              │     ├──────────────────────────┤
                        │  No authentication required  │     │  LexFind.ch              │
                        └──────────────────────────────┘     │  (links only)            │
                                                             └──────────────────────────┘

Data Source Characteristics

Design Decision: Tools-only (no MCP Resources)

All 8 endpoints are exposed as Tools rather than MCP Resources. Rationale:

• Every lookup is parametric — queries, abbreviations, article numbers vary per call. Static Resources (one URI per document) don't capture this naturally.
• The corpus is 974 laws × many articles — registering each as a Resource URI would create an impractically large resource list.
• MCP Resource templates (zhlex://laws/{sr_number}) are a future consideration for Phase 2 if clients benefit from resource-level caching or subscriptions.

Scaling Constraints

The Streamable-HTTP transport keeps session state in-process (FastMCP default). This has two implications:

• Single-instance only — horizontal scaling (multiple replicas) breaks active sessions because there is no shared session store (Redis, Durable Objects, etc.).
• No sticky-session LB needed today — a single-replica Render deployment naturally routes all requests to one process.

Before scaling beyond one instance: either add a shared session store or configure your edge load balancer to route on the Mcp-Session-Id header with a stick-table and an appropriate TTL.

MCP Protocol Version

Update policy

1. When mcp is upgraded (via Dependabot PR), verify the protocol version in the SDK release notes.
2. If the protocol version changes, update MCP_PROTOCOL_VERSION in server.py, regenerate docs/tool-hashes.json (PYTHONPATH=src python scripts/gen_tool_hashes.py --write), and note the change in CHANGELOG.md.
3. Run pytest tests/ -m "not live" to confirm compatibility before merging.

Project Structure

openlex-mcp/
├── src/openlex_mcp/
│   ├── __init__.py              # Package
│   ├── __main__.py              # Entry point for python -m
│   ├── server.py                # 8 MCP tool definitions (FastMCP) + Settings
│   ├── responses.py             # Typed structured response envelopes (SDK-002)
│   ├── logging_config.py        # structlog JSON logging setup (OBS-003)
│   ├── net.py                   # SSRF/egress-hardened outbound HTTP
│   ├── api_client.py            # zh.ch HTTP client + metadata extraction
│   ├── data_cache.py            # SQLite + FTS5 cache management
│   └── law_parser.py            # Article extraction from law texts
├── tests/                       # 89 unit tests (parser, cache, net, tools…)
├── scripts/gen_tool_hashes.py   # Tool-definition hash snapshot (SEC-022)
├── docs/                        # network-egress, secret-management, tool-hashes
├── .github/workflows/ci.yml     # GitHub Actions (Python 3.11/3.12/3.13)
├── .github/dependabot.yml       # Weekly dependency PRs (ARCH-012)
├── Dockerfile                   # Hardened multi-stage build (SEC-007/SCALE-004)
├── compose.yml                  # Resource limits for local testing (SCALE-006)
├── pyproject.toml
├── claude_desktop_config.json   # Example config for Claude Desktop
├── CHANGELOG.md
├── ROADMAP.md                   # Phase plan + accepted-risk register
├── CONTRIBUTING.md              # Contribution guide (English)
├── CONTRIBUTING.de.md           # Contribution guide (German)
├── SECURITY.md                  # Security policy (English)
├── SECURITY.de.md               # Security policy (German)
├── LICENSE
├── README.md                    # This file (English)
└── README.de.md                 # German version

Tool output format

All tools return a structured response envelope (not Markdown text), so MCP clients receive structuredContent they can parse directly:

{
  "source": "Kanton Zürich Rechtssammlung — HuggingFace … & zh.ch",
  "provenance": "cache",          // cache | live | parser | cache+parser | none
  "result_type": "law_summaries", // law_summaries | law_detail | articles | metadata | cache_status
  "count": 2,
  "message": null,                // human-readable guidance for empty/edge results
  "results": [ /* typed items */ ]
}

Known Limitations

• HuggingFace dataset: The html_content field is unreliable (cross-contaminated between laws); the server uses pdf_content instead, which is correct but has PDF extraction artefacts (hyphenation, layout artefacts)
• Article parser: PDF text extraction sometimes merges article boundaries; complex nested articles may not parse perfectly
• Initial load: First start requires ~25s to download and index 974 laws from HuggingFace (~38 MB SQLite database)
• zh.ch metadata: No official API; metadata extraction relies on HTML patterns that may change
• Offline mode: Full-text search works offline after initial load; live metadata requires internet
• The corpus is frozen at 2023-01-01. This is the limitation that matters most for a legal server, and it was the one not stated. The newest version in the entire dataset carries version_active_since = 2023-01-01; the HuggingFace dataset itself was last touched 2024-10-10. The 24-hour cache TTL and provenance="cache" describe where an answer came from, not how old the laws in it are. Every response now carries corpus_as_of and corpus_note alongside provenance.
• Repeals after the cut-off are invisible. All 974 entries carry is_active = True and not one has a version_inactive_since. That is not a server bug — the source lists only the statutes in force at snapshot time. The consequence is what matters: a law repealed since then still appears to be in force. Consult the ZH-Lex permalink for the operative text.
• zhlaw_update_cache does not make the laws newer. It re-downloads the same frozen dataset. Its docstring previously read "only call when law search results seem outdated", which suggested exactly the effect it does not have.

Safety & Limits

To report a vulnerability, see the Security Policy.

Testing

# Unit + contract tests (no network) — this is what CI runs
PYTHONPATH=src pytest tests/ -m "not live"

# Live tests against zh.ch and HuggingFace
PYTHONPATH=src pytest tests/ -m "live"

# Re-measure the corpus date and the live hosts
PYTHONPATH=src python scripts/record_fixtures.py

150 tests — 142 offline, 8 live. Eight tools, eight live tests: the best coverage in this portfolio, which is why the finding here is not about mechanics but about a confusion between two questions. provenance="cache" answers where an answer came from; corpus_as_of answers how old the laws in it are. Only the first was ever answered, and the second is the one a user means when they ask "is this current?".

A measurement limit, deliberately not resolved by editing a test

test_live_get_law_metadata fails in the recording environment: zhlex.zh.ch is not reachable from it. Nothing follows from that. Public DNS resolves the host (NOERROR, 194.247.8.174) and an NXDOMAIN control shows the query discriminates — so the limit is the environment's, not the source's.

The test was therefore left untouched. A test you see red because your own network cannot get out is not a test to rewrite; rewriting it would leave you measuring your own environment instead of the source. PROVENANCE.md records this as open.

Changelog

See CHANGELOG.md

Roadmap

See ROADMAP.md

Contributing

See CONTRIBUTING.md

Security

See SECURITY.md

License

MIT License — see LICENSE

Author

Hayal Oezkan · malkreide

Credits & Related Projects

• Data: rcds/swiss_legislation — HuggingFace dataset (CC-BY-SA 4.0)
• ZH-Lex: zh.ch Gesetzessammlung — Official Canton Zurich legal collection
• LexFind: lexfind.ch — Cross-cantonal legislation database
• Protocol: Model Context Protocol — Anthropic / Linux Foundation
• Related: swiss-courts-mcp — Law text + case law = complete legal research
• Related: zurich-opendata-mcp — Law text + city council decisions = full context
• Portfolio: Swiss Public Data MCP Portfolio

Installation

Run via uv's uvx — no clone or manual install needed. Add to your MCP client config (mcpServers for Claude Desktop, Cursor and Windsurf; use a top-level servers key for VS Code in .vscode/mcp.json):

{
  "mcpServers": {
    "openlex-mcp": {
      "command": "uvx",
      "args": [
        "openlex-mcp"
      ]
    }
  }
}