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

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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.

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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

Client	How to Connect
Claude.ai	Settings > Connectors > Add Integration > paste URL
Claude Code	claude mcp add japan-law --transport http https://japan-law-mcp.vercel.app/mcp
Claude Desktop	Add to config (see below)
GitHub Copilot	Add to VS Code settings (see below)

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"]
    }
  }
}

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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"

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Laws Covered

Law	Japanese Name	Act Number	Key Topic
Act on Protection of Personal Information (APPI)	個人情報の保護に関する法律	Act No. 57 of 2003 (amended 2020)	Personal data protection (EU adequacy)
Cybersecurity Basic Act	サイバーセキュリティ基本法	Act No. 104 of 2014	National cybersecurity framework
Telecommunications Business Act	電気通信事業法	Act No. 86 of 1984	Telecom regulation, communications secrecy
Companies Act	会社法	Act No. 86 of 2005	Corporate governance, shareholder rights
Act on Prohibition of Unauthorized Computer Access	不正アクセス行為の禁止等に関する法律	Act No. 128 of 1999	Anti-hacking, unauthorized access
My Number Act	行政手続における特定の個人を識別するための番号の利用等に関する法律	Act No. 27 of 2013	National ID number system
Constitution (selected provisions)	日本国憲法	1946	Fundamental rights, Article 13 (privacy basis)

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

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Deployment Tiers

Tier	Content	Database Size	Platform
Free	All major statutes + English translations + EU cross-references	~100-150 MB	Vercel (bundled) or local
Professional	+ Cabinet orders + ministerial ordinances + PPC guidelines + full regulatory corpus	~500 MB-800 MB	Azure Container Apps / Docker / local

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.

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Database Size Estimates

Component	Estimated Size	Notes
Major statutes (laws / 法律)	~40-50 MB	~200 key statutes, full Japanese text
English translations (JLT)	~30-40 MB	Official MOJ translations of major laws
EU cross-references	~5-10 MB	APPI-GDPR adequacy mapping tables
FTS5 indexes	~30-50 MB	Full-text search indexes for Japanese text (ICU tokenization)
Free tier total	~100-150 MB
Cabinet orders (政令)	~100-200 MB	Government orders implementing statutes
Ministerial ordinances (省令)	~150-250 MB	Ministry-level regulations
PPC guidelines	~20-50 MB	APPI interpretive guidelines
Professional tier total	~500 MB-800 MB

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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.

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Available Tools (13)

Core Legal Research Tools (8)

Tool	Description
search_legislation	FTS5 full-text search across all provisions with BM25 ranking
get_provision	Retrieve specific provision by statute + chapter/section
check_currency	Check if statute is in force, amended, or repealed
validate_citation	Validate citation against database (zero-hallucination check)
build_legal_stance	Aggregate citations from statutes for a legal topic
format_citation	Format citations per Japanese conventions (full/short/pinpoint)
list_sources	List all available statutes with metadata
about	Server info, capabilities, and coverage summary

EU/International Law Integration Tools (5)

Tool	Description
get_eu_basis	Get EU directives/regulations for Japanese statute
get_japanese_implementations	Find Japanese laws implementing EU act
search_eu_implementations	Search EU documents with Japanese implementation counts
get_provision_eu_basis	Get EU law references for specific provision
validate_eu_compliance	Check implementation status of EU directives

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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

Traditional Approach	This MCP Server
Search official databases by statute number	Search by plain language
Navigate multi-chapter statutes manually	Get the exact provision with context
Manual cross-referencing between laws	build_legal_stance aggregates across sources
"Is this statute still in force?" --> check manually	check_currency tool --> answer in seconds
Find EU basis --> dig through EUR-Lex	get_eu_basis --> linked EU directives instantly
No API, no integration	MCP protocol --> AI-native

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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.

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Security

This project uses multiple layers of automated security scanning:

Scanner	What It Does	Schedule
CodeQL	Static analysis for security vulnerabilities	Weekly + PRs
Semgrep	SAST scanning (OWASP top 10, secrets, TypeScript)	Every push
Gitleaks	Secret detection across git history	Every push
Trivy	CVE scanning on filesystem and npm dependencies	Daily
Socket.dev	Supply chain attack detection	PRs
Dependabot	Automated dependency updates	Weekly

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

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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.

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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

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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.

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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

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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

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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}
}

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License

Apache License 2.0. See LICENSE for details.

Data Licenses

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

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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

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_{Built with care in Stockholm, Sweden}