Japanese Law MCP Server

The e-Gov Laws alternative for the AI age.

Query Japanese legislation -- covering data protection, cybersecurity, corporate law, and more -- directly from Claude, Cursor, or any MCP-compatible client.

If you're building legal tech, compliance tools, or doing Japanese legal research, this is your verified reference database.

Built by Ansvar Systems -- Stockholm, Sweden

Why This Exists

Japanese legal research is scattered across official government databases, commercial legal platforms, and institutional archives. Whether you're:

• A lawyer validating citations in a brief or contract
• A compliance officer checking if a statute is still in force
• A legal tech developer building tools on Japanese law
• A researcher tracing legislative history

...you shouldn't need dozens of browser tabs and manual PDF cross-referencing. Ask Claude. Get the exact provision. With context.

This MCP server makes Japanese law searchable, cross-referenceable, and AI-readable.

Quick Start

Use Remotely (No Install Needed)

Connect directly to the hosted version -- zero dependencies, nothing to install.

Endpoint: https://japan-law-mcp.vercel.app/mcp

Claude Desktop -- add to claude_desktop_config.json:

{
  "mcpServers": {
    "japan-law": {
      "type": "url",
      "url": "https://japan-law-mcp.vercel.app/mcp"
    }
  }
}

GitHub Copilot -- add to VS Code settings.json:

{
  "github.copilot.chat.mcp.servers": {
    "japan-law": {
      "type": "http",
      "url": "https://japan-law-mcp.vercel.app/mcp"
    }
  }
}

Use Locally (npm)

npx @ansvar/japan-law-mcp

Claude Desktop -- add to claude_desktop_config.json:

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

{
  "mcpServers": {
    "japan-law": {
      "command": "npx",
      "args": ["-y", "@ansvar/japan-law-mcp"]
    }
  }
}

Cursor / VS Code:

{
  "mcp.servers": {
    "japan-law": {
      "command": "npx",
      "args": ["-y", "@ansvar/japan-law-mcp"]
    }
  }
}

Example Queries

Once connected, just ask naturally:

• "What does the Japanese data protection law say about consent?"
• "Search for cybersecurity requirements in Japanese legislation"
• "Is this statute still in force?"
• "Find provisions about personal data in Japanese law"
• "What EU directives does this Japanese law implement?"
• "Which Japanese laws implement the GDPR?"
• "Validate this legal citation"
• "Build a legal stance on data breach notification requirements"

Laws Covered

Additionally includes key PPC guidelines and supplementary materials:

• APPI Guidelines (General Rules, Cross-Border Transfer, etc.)
• PPC Q&A on APPI interpretation
• EU-Japan Adequacy Decision supplementary rules

Deployment Tiers

Deployment Strategy: MEDIUM - Dual Tier, Bundled Free

The free-tier database containing major statutes and English translations is estimated at 100-150 MB, within the Vercel 250 MB bundle limit. The free-tier database is bundled directly with the Vercel deployment. The professional tier with full cabinet orders, ministerial ordinances, and PPC guidelines requires local Docker or Azure Container Apps deployment.

Capability Detection

Both tiers use the same codebase. At startup, the server detects available SQLite tables and gates tools accordingly:

Free tier:     core_legislation, eu_references, english_translations
Professional:  core_legislation, eu_references, english_translations, cabinet_orders, ministerial_ordinances, ppc_guidelines

Tools that require professional capabilities return an upgrade message on the free tier.

Database Size Estimates

Language Support

The primary language is Japanese (ja), which is the sole legally binding version. Official English translations are available from the Japanese Law Translation portal (japaneselawtranslation.go.jp), maintained by the Ministry of Justice. These translations are explicitly marked as reference translations and are not legally authoritative.

The search tool supports queries in both Japanese and English, with Japanese queries using ICU-based tokenization for proper morphological analysis.

Available Tools (13)

Core Legal Research Tools (8)

EU/International Law Integration Tools (5)

Why This Works

Verbatim Source Text (No LLM Processing):

• All statute text is ingested from official Japanese government sources
• Provisions are returned unchanged from SQLite FTS5 database rows
• Zero LLM summarization or paraphrasing -- the database contains regulation text, not AI interpretations

Smart Context Management:

• Search returns ranked provisions with BM25 scoring (safe for context)
• Provision retrieval gives exact text by statute identifier + chapter/section
• Cross-references help navigate without loading everything at once

Technical Architecture:

Official Sources --> Parse --> SQLite --> FTS5 snippet() --> MCP response
                     ^                       ^
              Provision parser         Verbatim database query

Traditional Research vs. This MCP

Data Sources & Freshness

All content is sourced from authoritative Japanese legal databases:

• e-Gov Laws -- Official Japanese government legal database

Verified data only -- every citation is validated against official sources. Zero LLM-generated content.

Security

This project uses multiple layers of automated security scanning:

See SECURITY.md for the full policy and vulnerability reporting.

Important Disclaimers

Legal Advice

THIS TOOL IS NOT LEGAL ADVICE

Statute text is sourced from official Japanese government publications. However:

• This is a research tool, not a substitute for professional legal counsel
• Court case coverage is limited -- do not rely solely on this for case law research
• Verify critical citations against primary sources for court filings
• EU cross-references are extracted from statute text, not EUR-Lex full text

Before using professionally, read: DISCLAIMER.md | SECURITY.md

Client Confidentiality

Queries go through the Claude API. For privileged or confidential matters, use on-premise deployment.

Development

Setup

git clone https://github.com/Ansvar-Systems/Japan-law-mcp
cd Japan-law-mcp
npm install
npm run build
npm test

Running Locally

npm run dev                                       # Start MCP server
npx @anthropic/mcp-inspector node dist/index.js   # Test with MCP Inspector

Related Projects: Complete Compliance Suite

This server is part of Ansvar's Compliance Suite -- MCP servers that work together for end-to-end compliance coverage:

@ansvar/eu-regulations-mcp

Query 49 EU regulations directly from Claude -- GDPR, AI Act, DORA, NIS2, MiFID II, eIDAS, and more. Full regulatory text with article-level search. npx @ansvar/eu-regulations-mcp

@ansvar/us-regulations-mcp

Query US federal and state compliance laws -- HIPAA, CCPA, SOX, GLBA, FERPA, and more. npx @ansvar/us-regulations-mcp

@ansvar/security-controls-mcp

Query 261 security frameworks -- ISO 27001, NIST CSF, SOC 2, CIS Controls, SCF, and more. npx @ansvar/security-controls-mcp

@ansvar/automotive-cybersecurity-mcp

Query UNECE R155/R156 and ISO 21434 -- Automotive cybersecurity compliance. npx @ansvar/automotive-cybersecurity-mcp

30+ national law MCPs covering Australia, Brazil, Canada, China, Denmark, Finland, France, Germany, Ghana, Iceland, India, Ireland, Israel, Italy, Japan, Kenya, Netherlands, Nigeria, Norway, Singapore, Slovenia, South Korea, Sweden, Switzerland, Thailand, UAE, UK, and more.

Contributing

Contributions welcome! See CONTRIBUTING.md for guidelines.

Priority areas:

• Court case law expansion
• EU cross-reference improvements
• Historical statute versions and amendment tracking
• Additional statutory instruments and regulations

Roadmap

• Core statute database with FTS5 search
• EU/international law cross-references
• Vercel Streamable HTTP deployment
• npm package publication
• Court case law expansion
• Historical statute versions (amendment tracking)
• Preparatory works / explanatory memoranda
• Lower court and tribunal decisions

Citation

If you use this MCP server in academic research:

@software{japan_law_mcp_2025,
  author = {Ansvar Systems AB},
  title = {Japanese Law MCP Server: AI-Powered Legal Research Tool},
  year = {2025},
  url = {https://github.com/Ansvar-Systems/Japan-law-mcp},
  note = {Japanese legal database with full-text search and EU cross-references}
}

License

Apache License 2.0. See LICENSE for details.

Data Licenses

• Statutes & Legislation: Japanese Government (public domain)
• EU Metadata: EUR-Lex (EU public domain)

About Ansvar Systems

We build AI-accelerated compliance and legal research tools for the global market. This MCP server started as our internal reference tool -- turns out everyone building compliance tools has the same research frustrations.

So we're open-sourcing it.

ansvar.eu -- Stockholm, Sweden

_{Built with care in Stockholm, Sweden}