MCP server

Gengō-kun's API is also available as a Model Context Protocol (MCP) server. Install it into Claude Desktop, Claude Code, or any other MCP-compatible host to query Japanese calendar and holiday data in natural language.

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Package

`@matsubokkuri/seireki-mcp` is published on npm. Node.js 20 or later is required.

@matsubokkuri/seireki-mcp

terminal

Install

Install globally or invoke on demand with `npx`.

npm install -g @matsubokkuri/seireki-mcp
# or run on demand
npx -y @matsubokkuri/seireki-mcp

Client configuration

Add the following to Claude Desktop's `claude_desktop_config.json` or Claude Code's `.mcp.json`.

{
  "mcpServers": {
    "seireki": {
      "command": "npx",
      "args": ["-y", "@matsubokkuri/seireki-mcp"]
    }
  }
}

Override the base URL

Point the server at a staging deployment by setting the `SEIREKI_API_BASE_URL` environment variable.

{
  "mcpServers": {
    "seireki": {
      "command": "npx",
      "args": ["-y", "@matsubokkuri/seireki-mcp"],
      "env": {
        "SEIREKI_API_BASE_URL": "https://staging.seireki.example.com"
      }
    }
  }
}

Tools

The server exposes the following seven tools. Arguments are advertised to the host as JSON-Schema.

Tool	Description
`convert_seireki_to_wareki`	Convert a Western year to its Japanese era, age, and zodiac sign.
`convert_wareki_to_seireki`	Convert a year interpreted as Wareki to its Western counterpart.
`list_seireki_years`	Full Western-to-Japanese conversion table (1–3000).
`list_wareki_years`	Full Japanese-to-Western conversion table.
`get_holidays`	Public holidays for one Western year (1970 onward).
`list_holiday_years`	Per-year summary of holiday counts plus canonical URLs.
`get_holidays_ics`	Raw iCalendar (.ics) feed for one year.

Source & development

The implementation lives in this repository under `packages/mcp/`.

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