japan-utils-mcp

MCP server exposing Japan-specific utilities to AI agents (Claude, Cursor, Cline, Continue, etc.). Hand your agent the small bag of JP-specific functions every Japan-related task needs but no generic LLM gets right reliably:

• 🗓️ Era ↔ Western year — 令和8年 ↔ 2026

• 🔤 Kanji → Hepburn romaji — 山田太郎 → yamada tarou

• 📮 Postal code lookup — 150-0001 → 東京都 渋谷区 神宮前

• 🎌 National holiday calendar — is 2026-05-03 a holiday? what about all of 2026?

• 🅰️ Kana conversion — hiragana ↔ katakana ↔ half-width katakana

• 📏 Width normalization — full-width (全角) ↔ half-width (半角) for ASCII, digits, kana

• 👤 Name splitting — 山田太郎 → surname 山田 + given 太郎 (statistical model)

Built on top of well-maintained Japanese libraries (jpholiday, posuto, pykakasi, jaconv, namedivider-python) — wrapped as MCP tools so any AI agent can call them without re-implementing reading rules, era arithmetic, postal data, or name-splitting heuristics.

Why this exists

Generic LLMs hallucinate on JP-specific data:

• "What year is 令和8年?" — often wrong

• "Convert 山田太郎 to romaji" — gets the surname wrong half the time

• "What's the address for postal code 150-0001?" — fabricates plausible-looking nonsense

• "Is May 3rd a Japanese holiday?" — guesses

This MCP gives them a deterministic answer.

Tools

All tools return structured JSON. See tool docstrings in src/japan_utils_mcp/server.py for full schemas and examples.

Installation

Run with uvx (no install — recommended)

uvx japan-utils-mcp

That's it. uvx (from uv) handles install + run in one shot, isolated from your global Python.

From source

git clone https://github.com/vivek081166/japan-utils-mcp.git
cd japan-utils-mcp
uv sync
uv run japan-utils-mcp

Configuration

Claude Desktop

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

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

Claude Code

claude mcp add japan-utils -- uvx japan-utils-mcp

Cursor / Cline / Continue

Same JSON snippet as Claude Desktop, in their respective MCP config files.

Examples

Once connected, ask your agent things like:

What year is 令和8年? → era_to_western("令和8年") → 2026

What's the address for postal code 150-0001? → lookup_postal_code("150-0001") → 東京都 渋谷区 神宮前

Convert 山田太郎 to romaji. → kanji_to_romaji("山田太郎") → yamada tarou

Is May 3rd 2026 a Japanese holiday? → is_holiday("2026-05-03") → 憲法記念日 (Constitution Memorial Day)

List all Japanese holidays in 2026. → list_holidays(2026) → 18 holidays with names and dates

Convert ヤマダタロウ to hiragana. → convert_kana("ヤマダタロウ", "hiragana") → やまだたろう

Normalize ＡＢＣ１２３ to half-width. → normalize_width("ＡＢＣ１２３", "to_half") → ABC123

Split 長谷川健太 into surname and given name. → split_japanese_name("長谷川健太") → 長谷川 / 健太

Caveats

• Romaji of personal names uses the most common reading — proper nouns with unusual readings will be wrong. This is a fundamental limitation of any kanji-to-romaji conversion without disambiguation context.

• Postal code dataset ships via the posuto library, refreshed against Japan Post's monthly KEN_ALL. If you need ultra-fresh data, refresh posuto periodically.

• Holidays covers national holidays (国民の祝日) only — not company-specific or regional observances.

• Era conversion supports Meiji (明治) through Reiwa (令和). Earlier eras are not supported.

Development

git clone https://github.com/vivek081166/japan-utils-mcp.git
cd japan-utils-mcp
uv sync
uv run python -c "from japan_utils_mcp.server import era_to_western; print(era_to_western('令和8年'))"

License

MIT