mcp-jp-corporate-id

日本語版はこちら

An MCP (Model Context Protocol) server that validates and normalizes Japanese corporate numbers (houjin bangou) and qualified invoice issuer registration numbers, and normalizes/matches company names across common notation variants.

No network access is used at all (v1 calls no external APIs). Every check is done with formulas and dictionary data embedded in the code.

Read this first

• This tool only validates the format of numbers and names. It does NOT verify that a company actually exists, or that an invoice registration is currently valid. For real-world verification, always check the official National Tax Agency sites directly:
  • Corporate Number Publication Site
  • Qualified Invoice Issuer Publication Site
• Never enter a Japanese Individual Number (My Number). A company registration number (12 digits) and an individual My Number (12 digits) have the same length, and this tool cannot distinguish which kind of number it was given. calculate_check_digit always includes a caution about this in its response.
• This server never logs request input, and validation-error messages never echo back the raw number that was submitted.

Tools (7 total)

Every tool's response includes the primary sources (sources) behind its logic.

1. validate_corporate_number

Verifies whether the check digit of a 13-digit corporate number is correct. Accepts full-width digits, hyphens, and whitespace, which are normalized before validation. If the normalized length isn't 13 digits, or the check digit doesn't match, the tool returns valid: false rather than throwing.

2. calculate_check_digit

Computes the check digit from a 12-digit company registration number (assigned based on commercial registry records) and derives the 13-digit corporate number. Throws if the normalized input isn't exactly 12 digits (no guessing or zero-padding).

Caution: a 12-digit number could just as easily be a My Number (individual number) as a company registration number. Every response includes a caution field reminding callers never to submit a My Number. If the registry office code portion falls outside the typical range (0100–5000) confirmed from primary sources, a note is added.

3. validate_invoice_number

Validates a qualified invoice registration number ("T" + 13 digits).

• For numbers held by corporations ("T" + corporate number), the check digit is verified mathematically; a match returns entityType: "corporate".
• Numbers held by sole proprietors and unincorporated associations are separate 13-digit numbers issued by the NTA that overlap with neither My Number nor any corporate number. The check-digit algorithm for this class of number could not be confirmed as publicly documented within the primary sources reviewed. When the number doesn't match the corporate-number check-digit formula, the tool returns entityType: "individual_or_other", validates format only, and explicitly states that mathematical verification isn't possible in this case.
• If the input doesn't even match the "T" + 13 digits shape, formatValid: false is returned (not an exception).

4. parse_corporate_number

Verifies the check digit of a 13-digit corporate number and then parses the structure of its 12-digit base number.

• category: national_organ_legislative / national_organ_administrative / national_organ_judicial / local_government / registered_corporation / unregistered_corporation_or_unincorporated_association / unused_range
• For registered_corporation, returns registryOfficeCode (4 digits), organizationTypeCode (raw 2 digits), and serialNumber (6 digits).
• The mapping from the 2-digit organization type code to an actual corporate form (stock company, LLC, etc.) could not be confirmed as a documented numeric code table in the primary sources reviewed (the Commercial Registration Rules define three textual categories but the reviewed article text does not spell out numeric codes for them). The tool therefore returns only the raw 2-digit code with no label — see "Items that could not be verified" below.

5. normalize_company_name

Normalizes company-name notation and separates out the "body name" with the corporate form removed.

• Converts between major corporate-form notations (株式会社/(株)/（株）/㈱, etc.).
• Detects whether the corporate form appears as a prefix (株式会社○○) or suffix (○○株式会社).
• Normalizes full-width/half-width characters and a curated set of legacy/variant kanji forms (e.g. 髙→高, 﨑→崎).

Dictionary limits: only major corporate forms and variant characters are covered. This is not exhaustive of every Japanese corporate form or notation variant; anything not in the dictionary is left unrecognized and stays in the body name as-is.

6. generate_matching_key

Uses normalize_company_name internally and strips whitespace from the body name to produce a matching key for deduplication.

7. compare_company_names

Normalizes both names and compares them, returning a verdict, a confidence level, and reasons.

Design: the verdict and the reasons are both machine-generated from the same structured evidence

Rather than hand-writing the verdict/confidence logic and the explanatory text separately, this tool derives both from a single structured object, evidence, which is included as-is in the response:

The decision logic (evidence → verdict/confidence) and the explanation logic (evidence → reasons) are two separate functions that both read only from this same evidence object. Changing the decision rules automatically keeps the explanation in sync, so it's structurally impossible to end up with a confident verdict whose reasons/notes say "cannot be determined."

Script-mismatch guard (runs before any scoring)

If the two body names differ greatly in character type — one is Latin-only while the other contains Japanese (hiragana/katakana/kanji) — comparing them as strings is meaningless in principle. For example, "日本電気株式会社" (Nippon Electric Company) and "NEC" refer to the same company, yet their body-name strings share no characters at all ("NEC" is an abbreviation that cannot be detected by string comparison). Whenever this script mismatch is detected, the tool returns unknown (confidence: "low") immediately, before attempting any scoring.

Condition for returning likely_different

likely_different is returned only when all of the following hold:

• The two body names share a common prefix or suffix ("common token") of at least 2 characters.
• The remaining, non-shared part on each side (the "distinguishing element") is at least 2 characters long on both sides, and the two distinguishing elements differ.

Example: "東京電力" (Tokyo Electric Power) vs. "東北電力" (Tohoku Electric Power) — they share the suffix "電力" ("Electric Power") as a common token, with "東京" (Tokyo) and "東北" (Tohoku) as the distinguishing elements. Because both names follow the same naming pattern but diverge on a clear, region-identifying element, this tool treats them as likely different companies.

When this condition is not met (no shared part at all, or one name simply being a substring of the other), there is no positive evidence of being different companies, so the tool always returns unknown. The mere fact that two strings don't match or overlap is never, by itself, grounds for likely_different — string non-overlap is not evidence of being different entities. The reasons text distinguishes "no shared part at all" from "only a partial match" rather than using the same wording for both.

Confidence is capped at medium, and stays consistent with the verdict by construction

confidence has only two possible values: "medium" and "low". **"high" has been removed.** Since the 2006 enactment of the Companies Act abolished the similar-trade-name restriction, two unrelated companies can be registered under the same name as long as their head-office locations differ — so a match based on trade name alone can never justify strong confidence ("high"`) in principle.

The set of valid confidence values is constrained per verdict at the TypeScript type level: unknown can only ever carry confidence: "low", and both likely_same and likely_different can only ever carry confidence: "medium". It is structurally impossible for this tool to return unknown together with confidence: "medium".

This tool never "hedges by lowering confidence." When something is inherently indeterminate — such as the prefix/suffix placement mismatch below — the tool sets verdict itself to unknown rather than downgrading likely_same to a lower confidence. This matters for callers that branch purely on verdict (e.g. a batch job that auto-merges everything marked likely_same): such a caller would silently swallow the ambiguity if it were only reflected in confidence.

reasons always states concretely why the tool reached its conclusion — or why it couldn't (script mismatch, no shared token, partial overlap only, a mismatched corporate form or prefix/suffix placement, possibility of an abbreviation/English name, etc.), generated directly from evidence. Every response also includes a fixed note on the method's limitations:

This tool only performs text comparison based on notation normalization; it cannot judge whether an abbreviation, English name, or nickname refers to the same entity. A definitive identity check requires cross-referencing corporate numbers.

What this tool can and cannot determine

The only case where this tool returns likely_same (medium) is when the body name, corporate form, and prefix/suffix placement all match. Even when the body name appears to match, a differing prefix/suffix placement or a differing corporate form leaves a real possibility of a different entity that cannot be ruled out in principle, so the tool returns unknown. likely_different is returned only when the strict "shared pattern

• clearly different identifier" condition above is met. Every other case is unknown. unknown does not mean "probably different" — it means "this method cannot determine it." When a definitive identity check is required, obtain each company's corporate number and cross-reference with validate_corporate_number or similar.

Primary sources

The number-validation logic was implemented only after retrieving and reading the following primary sources directly (last checked: 2026-07-29):

• Check-digit formula: NTA Corporate Number site, "Check Digit Calculation" https://www.houjin-bangou.nta.go.jp/documents/checkdigit.pdf
• Corporate number (13-digit) structure: NTA Corporate Number site, "Structure of the Corporate Number" https://www.houjin-bangou.nta.go.jp/documents/houjinbangounokousei.pdf
• Overview of the corporate number system (who is assigned a number; categories for national organs, local governments, registered corporations, etc.): NTA Corporate Number Management Office, "About the Corporate Number" (June 2026 edition) https://www.houjin-bangou.nta.go.jp/setsumei/pamphlet/images/houjinbangou_gaiyou.pdf
• Act on the Use of Numbers to Identify a Specific Individual in Administrative Procedures, Article 39: https://laws.e-gov.go.jp/law/425AC0000000027
• Its Cabinet Order (Cabinet Order No. 155 of 2014), Articles 35 (corporate number structure) and 36 (units for assigning numbers to national organs): https://laws.e-gov.go.jp/law/426CO0000000155
• Ordinance on the Assignment of Corporate Numbers (MOF Ordinance No. 70 of 2014), Articles 2 (check-digit formula) and 3 (base numbers for non-registered entities): https://laws.e-gov.go.jp/law/426M60000040070
• Commercial Registration Rules (Ministry of Justice Ordinance No. 23 of 1964), Article 1-2 (recording of company registration numbers): https://laws.e-gov.go.jp/law/339M50000010023
• Invoice registration number structure: NTA Qualified Invoice Issuer Publication Site, "About Registration Numbers" https://www.invoice-kohyo.nta.go.jp/about-toroku/index.html

Items that could not be verified (disclosed honestly)

• The specific numeric code table for the 2-digit "organization type" portion of the company registration number (e.g. which digits mean "stock company" vs. "LLC") could not be confirmed. Article 1-2 of the Commercial Registration Rules defines three textual categories ("stock companies"; "general/limited partnerships, LLCs, and foreign companies"; "trade-name users, etc."), but the reviewed statutory text does not spell out numeric codes for them, and secondary sources (blog posts, etc.) found online disagreed with each other. Because of this, parse_corporate_number returns only the raw 2-digit code with no interpretive label.
• What the local-government sub-codes ("20" / "30") specifically distinguish (e.g. prefectures vs. municipalities) could not be confirmed.
• The check-digit algorithm for the 13-digit invoice registration numbers issued to sole proprietors and unincorporated associations could not be confirmed as publicly documented. Numbers in this category are therefore validated for format only, with no mathematical check-digit verification.
• The corporate-form and legacy-kanji dictionaries are not an exhaustive statutory definition; they are a practical, hand-curated set of commonly seen notations.

Setup

1. Prerequisites

• Node.js (LTS recommended)

node --version

2. Install dependencies

npm install

3. Build

npm run build

On success, build/index.js is created.

Using it from Claude Desktop

Add the following to your Claude Desktop config file (claude_desktop_config.json):

{
  "mcpServers": {
    "jp-corporate-id": {
      "command": "node",
      "args": ["/absolute/path/to/mcp-jp-corporate-id/build/index.js"]
    }
  }
}

Config file locations:

• Windows: %APPDATA%\Claude\claude_desktop_config.json
• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json

Restart Claude Desktop afterward, and tools such as validate_corporate_number become available.

Running tests

npm test

All tests should show ✔.

Project layout

mcp-jp-corporate-id/
├── src/
│   ├── sources.ts          … list of cited primary sources
│   ├── errors.ts            … shared validation-error class
│   ├── normalize.ts         … full/half-width, hyphen, etc. input normalization
│   ├── checkDigit.ts        … the check-digit formula
│   ├── corporateNumber.ts   … 12-digit base-number structure parsing
│   ├── corporateIdCalc.ts   … logic for tools 1-4
│   ├── companyNameData.ts   … corporate-form dictionary, legacy-kanji map
│   ├── companyName.ts       … logic for tools 5-7
│   └── index.ts             … MCP server entry point (registers the 7 tools)
├── tests/                   … automated tests (node:test)
├── package.json
├── tsconfig.json
├── LICENSE
├── README.md                … this file
└── README.ja.md             … Japanese version

Related tools

Other servers by the same author:

• mcp-jp-paid-leave — an MCP server for calculating statutory annual paid leave under Japan's Labor Standards Act
• mcp-jp-calendar — an MCP server for Japanese business days, national holidays, gotobi settlement days, and fiscal quarters

License

MIT