Japan Law MCP Server

@pipeworx/japan-law

Japanese national laws, cabinet orders, and ministerial ordinances — title search, a law's full text (paged), and a single article (including branch articles like 第二十七条の2) at its current or a point-in-time version — from e-Gov 法令検索, the Japanese government's official law portal.

Part of Pipeworx — an MCP gateway connecting AI agents to 1865+ live data sources. This is an independent, unofficial integration — not affiliated with, endorsed by, or published by the upstream provider.

Tools

• search_laws(query, limit?) — TITLE search only: finds laws whose title matches a keyword ("個人情報", "労働基準"). Does not search the body text of a law. Returns each match's law id, law number, title and type.
• japan_law_get_article(law_id, article, as_of?) — the text of a single article, by law id (from search_laws) and article number. article accepts "27", "27条の2", "27-2", "27_2", or the kanji form "第二十七条の2" — all branch-article spellings resolve to the same lookup. Returns just that article's caption, heading and text — far cheaper than paging through get_law to find one provision. Pass as_of (YYYY-MM-DD) to get the article as it stood on that date, e.g. before or after a given amendment.
• get_law(law_id, as_of?, offset?, limit?) — a law's metadata plus its full text, PAGED by character offset: has_more / next_offset say whether another page follows; a long law is never silently cut off with no way to continue. Pass as_of for the version of the law in force on a given date.

Every response carries source (publisher + dataset) and, where the law versions, revision_date (the actual effective date of the revision returned) alongside the as_of the caller asked for.

Auth

Keyless. e-Gov's law API is open to the public with no registration.

Data source

e-Gov 法令検索 (Japan's e-Government law portal), the Japanese government's official, keyless law search and text API — the same data Japan's courts, ministries and legal publishers cite. Point-in-time (as_of) support follows the portal's own revision history: each law carries every revision the portal has recorded, and as_of resolves to the revision in force on that date.

Coverage and what is not here

• Search is TITLE matching only. There is no full-text (body) search across the statute corpus — a query that only appears inside a law's articles, not its title, will not find that law.
• japan_law_get_article looks up the first article with a matching number in document order, which in every law checked during this build is the article in the main provisions (本則). A law whose supplementary provisions (附則) reuse the same article numbering is not specially disambiguated.
• Branch-article parsing covers the kanji numerals articles actually use (one to several thousand); it is not a general kanji-numeral parser for arbitrary magnitudes.

Quick Start

Add to your MCP client (Claude Desktop, Cursor, Windsurf, etc.):

{
  "mcpServers": {
    "japan-law": {
      "url": "https://gateway.pipeworx.io/japan-law/mcp"
    }
  }
}

What this endpoint actually serves

tools/list at https://gateway.pipeworx.io/japan-law/mcp returns the tools in the table above plus the shared Pipeworx meta-tools — ask_pipeworx, discover_tools, search_within, remember/recall and the rest of the gateway-wide set. So the tool count you see is larger than this table: a single-pack endpoint currently lists roughly 30 shared tools alongside the pack's own. The connection's initialize response states its exact scope, and is the authoritative answer for a given day.

This is deliberate, not multiplexing by accident. The meta-tools are what let a scoped connection answer a question this pack does not cover — via ask_pipeworx, which routes across the whole catalog — without you adding a second MCP server. There is currently no way to mount a pack endpoint without them; if the extra schemas cost you more context than the routing is worth, connect to the full gateway once rather than to several pack endpoints.

Or connect to the full Pipeworx gateway to get every pack's tools listed directly, instead of just this one's:

{
  "mcpServers": {
    "pipeworx": {
      "url": "https://gateway.pipeworx.io/mcp"
    }
  }
}

Both URLs reach the same gateway and the same 1865+ data sources. The only difference is which pack's tools are listed directly; ask_pipeworx reaches all of them from either one.

No MCP client? Call it over HTTP

curl -X POST https://gateway.pipeworx.io/v1/tools/search_laws \
  -H 'Content-Type: application/json' \
  -d '{"query":"個人情報保護"}'

No account needed for the first calls. Inspect any tool: GET https://gateway.pipeworx.io/v1/tools/search_laws. Find one: POST https://gateway.pipeworx.io/v1/tools/search_packs with {"query":"..."}.

Run it from npm

@pipeworx/mcp-japan-law is a local stdio bridge to the Pipeworx gateway: your MCP client starts it with npx, and it forwards every call to the same https://gateway.pipeworx.io/japan-law/mcp endpoint shown above. It needs network access; there is no offline mode.

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

Without a key it calls anonymously, capped at 50 calls a day. A free account raises that to 200 a day: get a key at https://pipeworx.io/signup and add "env": { "PIPEWORX_API_KEY": "<your key>" } to the server entry. The key is sent as a Bearer token, the same way a hosted connection sends it, so calls are metered and billed exactly as they are there.

It lists only this pack's tools by default. Set PIPEWORX_META_TOOLS=1 to also list ask_pipeworx and the other gateway-wide tools.

Behind an HTTPS proxy: Node's built-in fetch does not read HTTPS_PROXY by default. Newer Node releases honour it when NODE_USE_ENV_PROXY=1 is set; check your Node version's documentation.

Using with ask_pipeworx

Instead of calling tools directly, you can ask questions in plain English — this works on the pack endpoint above as well as on the full gateway:

ask_pipeworx({ question: "your question about Japan Law data" })

The gateway picks the right tool and fills the arguments automatically.

More

• Docs and guides
• pipeworx.io

License

MIT