Openlex

🇨🇭 Part of the Swiss Public Data MCP Portfolio

⚖️ openlex-mcp

License: MIT Python 3.11+ MCP No Auth Required

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

🇩🇪 Deutsche Version

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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.

Source	Data	Access
HuggingFace	974 ZH laws — full text (PDF extracts)	Cached locally as SQLite + FTS5
zh.ch ZH-Lex	Current metadata, PDF links, validity status	Live HTTP requests

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'."

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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)

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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.

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Prerequisites

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

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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 .

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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'?"

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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."

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Available Tools

Search & Browse

Tool	Description
openlex__zhlaw_search_laws	Full-text search across all ~970 ZH laws (FTS5 + BM25 ranking)
openlex__zhlaw_get_law	Retrieve a law by LS number (e.g. 412.100) or abbreviation (e.g. VSG)
openlex__zhlaw_list_laws	List and filter laws by legal area prefix
openlex__zhlaw_find_education_laws	Specialized search in education law (LS 412.x series)

Article Extraction

Tool	Description
openlex__zhlaw_get_article	Extract a specific article from a law (e.g. Art. 28 VSG)
openlex__zhlaw_search_articles	Search within all articles of a specific law

Metadata & Cache

Tool	Description
openlex__zhlaw_get_law_metadata	Get live metadata from zh.ch (PDF links, validity status)
openlex__zhlaw_update_cache	Refresh the local data cache from HuggingFace

Key Legal Area Prefixes (LS Numbers)

Prefix	Legal Area	Example
131	Constitution and popular rights	Kantonsverfassung
170	Administrative procedure	Datenschutzgesetz
331	Tax law	Steuergesetz
412	Education and schools	Volksschulgesetz (VSG)
700	Spatial planning and building	Planungs- und Baugesetz
810	Health	Gesundheitsgesetz

Example Use Cases

Query	Tool
"What is the Volksschulgesetz?"	openlex__zhlaw_get_law
"Find laws about data protection"	openlex__zhlaw_search_laws
"Show me Art. 55 VSG"	openlex__zhlaw_get_article
"Which education laws mention Schulleitung?"	openlex__zhlaw_find_education_laws
"Find all articles about Elternrat in the VSG"	openlex__zhlaw_search_articles
"Is LS 412.100 still in force?"	openlex__zhlaw_get_law_metadata

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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

Source	Protocol	Coverage	Auth	License
HuggingFace rcds/swiss_legislation	Datasets API	974 ZH laws (full text)	None	CC-BY-SA 4.0
zh.ch ZH-Lex	HTTP/HTML	Current metadata, PDFs	None	Public
LexFind.ch	HTTP	Cross-cantonal links	None	Public

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.

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MCP Protocol Version

Item	Value
Served via the initialize handshake	2024-11-05 … 2025-11-25 — the handshake ceiling
Served via the per-request envelope	2026-07-28
Who picks	The client's first request, once per connection. A request carrying the 2026-07-28 _meta envelope opens a modern connection; anything else opens a handshake connection.
SDK	mcp[cli]>=2.0.0,<3
Cache hints	tools/list and server/discover: ttlMs 300000, cacheScope public
Pinned in	src/openlex_mcp/server.py — MCP_PROTOCOL_VERSION constant

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.

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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 */ ]
}

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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.

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Safety & Limits

Aspect	Details
Access	Read-only (readOnlyHint: true) — the server cannot modify or delete any data
Personal data	No personal data — all sources are aggregated, public legal texts
Rate limits	Built-in per-query caps (max 50 search results, 5000 chars content preview)
Timeout	30 seconds per HTTP call to zh.ch
Egress	Outbound requests are restricted to an allow-list (www.zh.ch over HTTPS, plus the HTTP-only legacy permalink host www.zhlex.zh.ch), with SSRF IP-blocking and DNS-pinning — see docs/network-egress.md
Authentication	No API keys required — HuggingFace dataset is public, zh.ch is open
Security posture (Lethal Trifecta)	Score 1 / 3: public data only (no private/sensitive data) ✓ · GET-only egress to *.zh.ch — no POST, no webhooks, no email ✓ · no code execution ✓. Structurally safe by design.
Session handling	Mcp-Session-Id generated and managed by the MCP SDK (cryptographically secure UUIDs). No user-identity binding — auth_model=none is correct for public read-only data. If authentication is ever added, bind sessions to the validated OAuth sub claim before deployment.
Secrets	No secrets held — all data sources are public. See docs/secret-management.md.
Licenses	Law data: CC-BY-SA 4.0 (rcds/swiss_legislation); zh.ch metadata: public
Terms of Service	Subject to ToS of HuggingFace and Canton Zurich
Disclaimer	This server provides legal texts for informational purposes only — it does not constitute legal advice

To report a vulnerability, see the Security Policy.

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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.

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Changelog

See CHANGELOG.md

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Roadmap

See ROADMAP.md

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Contributing

See CONTRIBUTING.md

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Security

See SECURITY.md

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License

MIT License — see LICENSE

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Author

Hayal Oezkan · malkreide

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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"
      ]
    }
  }
}