open-zeimu-mcp

open-zeimu-mcp is an OSS MCP server for Japanese tax primary sources. The current repo ships lexical search, tax-answer category/retrieval tools, tsutatsu retrieval/search, qa-case retrieval/search, written-answer retrieval/search, e-Gov law lookup, and a tax-answer crawler that writes normalized Markdown data into data/tax_answer/.

What is open-zeimu-mcp?

Zero-setup MCP server for Japanese tax primary-source retrieval
Designed for npm install @zeimu-ai/open-zeimu-mcp
Built on the official Model Context Protocol TypeScript SDK
Intended to grow toward circulars, rulings, and optional semantic search

Quick Start

npm install @zeimu-ai/open-zeimu-mcp

Example MCP client configuration:

{
  "mcpServers": {
    "open-zeimu-mcp": {
      "command": "npx",
      "args": ["-y", "@zeimu-ai/open-zeimu-mcp"],
      "env": {
        "EMBEDDING_BACKEND": "none",
        "LOG_LEVEL": "info",
        "DATA_DIR": "./data"
      }
    }
  }
}

Features

health: reports runtime health, uptime, and directory readiness
stats: reports per-source document counts and lexical index readiness
lexical_search: searches packaged Markdown tax documents in memory
list_tax_answer_categories: lists packaged Tax Answer categories
get_tax_answer: returns packaged Tax Answer content by ID
search_tax_answer: searches packaged Tax Answer content only
list_tsutatsu_categories: lists packaged tsutatsu categories
get_tsutatsu: returns packaged tsutatsu content by ID
search_tsutatsu: searches packaged tsutatsu content only
list_qa_case_categories: lists packaged QA-case categories
get_qa_case: returns packaged QA-case content by ID
search_qa_case: searches packaged QA-case content only
get_written_answer: returns packaged written-answer content by ID
search_written_answer: searches packaged written-answer content only
get_law: fetches law text from e-Gov Law API v2 by law name (24h cache)
search_law: searches laws by keyword via e-Gov Law API v2 (24h cache)
crawl:tax-answer: crawls NTA Tax Answer pages into Markdown + metadata
Structured output schemas for MCP clients that support typed tool responses
No API key required (e-Gov Law API v2 is free and open)

Configuration

| Variable | Default | Description | | --- | --- | --- | | EMBEDDING_BACKEND | none | none, local, or supabase | | LOG_LEVEL | info | Pino log level | | DATA_DIR | ./data | Root directory for packaged dataset files | | VECTORS_CACHE_DIR | ~/.cache/open-zeimu-mcp/vectors | Local vector cache path |

This package reads configuration from process.env only. It does not load a .env file.

e-Gov Law Tool Example

Fetch a law by name:

{
  "name": "get_law",
  "arguments": {
    "law_name": "印紙税法",
    "format": "markdown"
  }
}

Search laws by keyword:

{
  "name": "search_law",
  "arguments": {
    "query": "印紙税",
    "limit": 5
  }
}

Results are cached in memory for 24 hours. No API key is required.

Tax Answer Tool Examples

Fetch a tax answer by ID:

{
  "name": "get_tax_answer",
  "arguments": {
    "id": "1200"
  }
}

Search only within packaged tax answers:

{
  "name": "search_tax_answer",
  "arguments": {
    "query": "基礎控除",
    "limit": 5
  }
}

List packaged tax-answer categories:

{
  "name": "list_tax_answer_categories",
  "arguments": {}
}

Written Answer Tool Examples

Fetch a written answer by ID:

{
  "name": "get_written_answer",
  "arguments": {
    "id": "202401"
  }
}

Tsutatsu Tool Examples

Fetch a tsutatsu document by ID:

{
  "name": "get_tsutatsu",
  "arguments": {
    "id": "tsu-001"
  }
}

Search only within packaged tsutatsu documents:

{
  "name": "search_tsutatsu",
  "arguments": {
    "query": "仕入税額控除",
    "limit": 5
  }
}

List packaged tsutatsu categories:

{
  "name": "list_tsutatsu_categories",
  "arguments": {}
}

QA Case Tool Examples

Fetch a QA case by ID:

{
  "name": "get_qa_case",
  "arguments": {
    "id": "qa-001"
  }
}

Search only within packaged QA cases:

{
  "name": "search_qa_case",
  "arguments": {
    "query": "交際費",
    "limit": 5
  }
}

List packaged QA-case categories:

{
  "name": "list_qa_case_categories",
  "arguments": {}
}

Search only within packaged written answers:

{
  "name": "search_written_answer",
  "arguments": {
    "query": "第2ページ",
    "limit": 5
  }
}

Tax Answer Crawler

The crawler fetches NTA Tax Answer pages from www.nta.go.jp, respects robots.txt, enforces 1 req/sec, and writes only parsed Markdown / JSON metadata. Raw HTML is never persisted.

Dry run against specific IDs:

npm run crawl:tax-answer -- --ids 1200,3105 --data-dir ./data --repo-dir .

Apply changes and push a bot commit:

npm run crawl:tax-answer -- --apply --limit 50 --data-dir ./data --repo-dir .

Generated files follow:

data/tax_answer/<id>/<id>.md
data/tax_answer/<id>/<id>.meta.json

The metadata file includes content_hash, aliases, headings, etag, last_modified, and version.

Status

Under active development. The current implemented surface covers PR-2 lexical search, PR-3 tax-answer crawling, PR-4 packaged retrieval/search across tax-answer, tsutatsu, qa-case, and written-answer, plus PR-5 e-Gov law retrieval on the path to v0.1.0.

Lexical Search Example

Tool call:

{
  "name": "lexical_search",
  "arguments": {
    "query": "基礎控除",
    "source_types": ["tax_answer"],
    "limit": 5
  }
}

Example response:

{
  "hits": [
    {
      "id": "1200",
      "source_type": "tax_answer",
      "title": "所得税の基礎控除",
      "score": 42.1,
      "snippet": "所得税の基礎控除は、一定額を所得から差し引く制度です。"
    }
  ]
}

Development

npm install --include=dev
npm run typecheck
npm test
npm run build
npm start

More details:

Architecture: docs/architecture.md
Tool API examples: docs/api.md
Testing notes: docs/TESTING.md

Data Sources and Licenses

Source-specific attribution and downstream license notices will be expanded as data loaders land. See NOTICE.

License

MIT

MCP Servers