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PopNx MCPAIを使う人のためのMCPサーバー · やさしい言葉で解説

日本の給与・社会保険・労働法

作者:kishida-devilバージョン 0.4.5i★ 3iパソコンでもクラウドでも
レジストリ名io.github.kishida-devil/jp-payroll-mcp

インストール

概要

作者による説明(英語の原文)

Japan payroll & social insurance. 日本の給与計算・社会保険。47都道府県の料率、源泉所得税、割増賃金、有給、標準報酬月額の改定、最低賃金。根拠の条文つき。

PopNx MCPの3つの柱

この3つを1つのスコアにまとめることはしません。意見、測定、人気はそれぞれ別のものだからです。

できること

このサーバーのやさしい解説はまだ書いていません。以下はレジストリから読み取った事実です。

  • 接続方法: パソコンでもクラウドでも
  • トランスポート: stdio, Streamable HTTP
  • カテゴリ: 会計・財務・税務

インストール

使っているAIアプリを選んで、設定をコピーしてください。

インストールの前に

必要なもの

  • クラウドで動くインストール不要。インターネット経由でつながります
  • npmNode.jsのインストール(npxコマンドに必要)

どのアプリを使っていますか?

上でアプリを選んでください。選んだアプリを覚えておくので、次からはボタンに「…にインストール」と表示されます。

ウェブ、デスクトップ、モバイルのClaudeで使えます:

  1. Settings → Connectors を開く
  2. Add custom connector を押す
  3. 下のアドレスを貼り付けて Add を押す
  4. サインインを求められたら、作者のサービスにサインインする
SettingsConnectors1+ Add2https://…3Connect4
https://japan-payroll-api.tsumugi.workers.dev/mcp

または、パソコンで動かす

Claude Desktop → Settings → Developer → Edit Config を開き、claude_desktop_config.json にこれを貼り付けます

{
  "mcpServers": {
    "jp-payroll": {
      "command": "npx",
      "args": [
        "-y",
        "jp-payroll-mcp"
      ]
    }
  }
}

ターミナルでこれを実行します

claude mcp add --transport http jp-payroll https://japan-payroll-api.tsumugi.workers.dev/mcp

または、パソコンで動かす

claude mcp add jp-payroll -- npx -y jp-payroll-mcp

Cursorで開く

または、設定を自分でコピーする

プロジェクトの .cursor/mcp.json、または ~/.cursor/mcp.json に貼り付けます

{
  "mcpServers": {
    "jp-payroll": {
      "url": "https://japan-payroll-api.tsumugi.workers.dev/mcp"
    }
  }
}

または、パソコンで動かす

Cursorで開く

または、設定を自分でコピーする

プロジェクトの .cursor/mcp.json、または ~/.cursor/mcp.json に貼り付けます

{
  "mcpServers": {
    "jp-payroll": {
      "command": "npx",
      "args": [
        "-y",
        "jp-payroll-mcp"
      ]
    }
  }
}

ブラウザがアプリを開いてよいか確認し、そのあとアプリが設定を表示して確認を求めます。キーの値は空欄のままなので、自分で入力してください。

VS Codeで開く

または、設定を自分でコピーする

プロジェクトの .vscode/mcp.json に貼り付けます

{
  "servers": {
    "jp-payroll": {
      "type": "http",
      "url": "https://japan-payroll-api.tsumugi.workers.dev/mcp"
    }
  }
}

または、パソコンで動かす

VS Codeで開く

または、設定を自分でコピーする

プロジェクトの .vscode/mcp.json に貼り付けます

{
  "servers": {
    "jp-payroll": {
      "type": "stdio",
      "command": "npx",
      "args": [
        "-y",
        "jp-payroll-mcp"
      ]
    }
  }
}

ブラウザがアプリを開いてよいか確認し、そのあとアプリが設定を表示して確認を求めます。キーの値は空欄のままなので、自分で入力してください。

ChatGPTがつなげるのは、インターネット上のサーバーだけです:

  1. ウェブ版のChatGPTを開き → Settings → Connectors (Apps)
  2. Create または Add を押す(プランによっては、先に Advanced で Developer mode をオンにする必要があります)
  3. 下のアドレスを貼り付け、名前を付けて保存する
  4. サインインを求められたら、作者のサービスにサインインする
SettingsConnectors1+ Create2https://…3Connect4
https://japan-payroll-api.tsumugi.workers.dev/mcp

メニューの名前は、プランや時期によって少し違うことがあります。

選んだアプリは、この端末のCookieに保存されます。アカウントは不要です。

この設定は、作者のレジストリ登録情報から作成しています。READMEと違う場合は、READMEに従ってください。

使えるアプリ

このサーバーのつなぎ方と、各アプリの公式ドキュメントに基づきます。2026年11月10日に確認。

インターネット経由でつなげるアプリ

ClaudeChatGPTGooseLM StudioMsty StudioCherry StudioCursorVS Code + GitHub CopilotVisual StudioWindsurf (Devin Desktop)ZedKiroClineContinueJetBrains AI AssistantClaude CodeCodex CLIGemini CLIOpenCodenodecodeWarpLibreChatOpen WebUIRaycast

パソコン上で動かせるアプリ

ClaudeGooseLM StudioMsty StudioCherry StudioCursorVS Code + GitHub CopilotVisual StudioWindsurf (Devin Desktop)ZedKiroClineContinueJetBrains AI AssistantClaude CodeCodex CLIGemini CLIOpenCodenodecodeWarpLibreChatRaycast

すべてのアプリと長所・短所 →

できること

ツールの名前と説明は、サーバーが2026年11月10日に返したそのままの内容です。書いたのは作者で、私たちではありません。プレーンテキストとして表示しています。

  • calculate_payslip

    Full monthly deduction breakdown for one employee: health insurance, long-term care, pension, child support, employment insurance, withholding income tax and net pay, with the employer share as well. Use this rather than computing it yourself. Premiums are charged on 標準報酬月額 — a 5

  • list_workers_compensation_rates

    Workers compensation (労災保険) rates by business type, and the employer premium on a given 賃金総額. The whole premium falls on the employer — nothing is deducted from the employee, unlike every other statutory premium. Rates run from 2.5/1000 to 88/1000 depending on the industry, a 35-

  • calculate_bonus

    Premiums and income tax on a 賞与. Both work differently from monthly pay and are routinely got wrong. Premiums are charged on 標準賞与額 (the bonus truncated to the thousand yen) under two caps that behave differently: health, long-term care and child support cap at 5,730,000 yen CUMUL

  • calculate_withholding_tax

    Income tax to withhold from a payment, from the National Tax Agency tables. The taxable amount is pay AFTER social insurance has been deducted, not gross. Pick the table with `period`: "monthly" for 月額表, "daily" for 日額表. The daily table has a third column, 丙, which applies to wor

  • judge_monthly_revision

    Decides whether a pay change forces the standard remuneration to be revised, and answers SEPARATELY for health insurance and pension — the tables differ, so a change routinely moves one and not the other. Above roughly 665,000 yen the pension table is exhausted, so a large raise

  • decide_regular_remuneration

    The yearly redetermination of standard remuneration, effective each September through the following August. Months below the payment-basis-day threshold drop OUT of the average entirely — they are not counted as zero, which is the usual mistake. If no month qualifies, the previou

  • judge_leave_end_revision

    A separate route with a lower bar than 随時改定, and the one people forget. ONE grade of movement is enough, and fixed pay need not have changed at all — which matters because returning to shorter hours usually cuts pay without changing any rate, so 随時改定 would not fire and the employ

  • calculate_payroll_batch

    Runs calculate_payslip for many employees in one call and returns the run totals: gross, employee deductions, net, and employer cost. Reach for this the moment more than two or three people are in play. A monthly payroll is not a sequence of unrelated questions — the employer sha

  • decide_regular_remuneration_batch

    Runs the annual 定時決定 for a whole payroll in one call, and reports which employees moved grade. 健康保険法第41条 puts every insured employee on the same schedule — the average of April, May and June pay, over the months with at least seventeen payment-basis days, applied from September t

  • judge_annual_average

    For work whose April-June happens to be its busiest or quietest quarter, where the ordinary calculation would fix a grade that is wrong for eleven months of the year. Available for 定時決定 (since April 2011) and 随時改定 (since October 2018). The 随時改定 figure is NOT a plain twelve-month

  • lookup_standard_remuneration

    Maps a monthly amount to its health grade (1-50) and pension grade (1-32), with the standard remuneration each resolves to and whether the pension grade was clamped. Use it to check a grade, not to compute premiums — calculate_payslip does that.

  • national_insurance

    For anyone outside employee cover: the self-employed, freelancers, people between jobs. Use this instead of calculate_payslip when the person is not an employee. Running a freelancer through the payslip returns a figure computed under a different scheme entirely, with nothing in

  • calculate_annual_cost

    What one employee costs an employer over a year, bonuses included. Reach for this rather than multiplying a payslip by twelve, because the two do not agree once a bonus is paid. 健康保険法第45条 caps the standard bonus cumulatively across the year — 5,730,000 from 1 April to 31 March —

  • judge_annual_leave

    Works out how many days of paid leave someone has been granted, and whether the employer still owes the five days it must direct. 労働基準法第39条 grants ten working days once six months of service are complete and attendance reaches eighty per cent of all working days, then adds one, t

  • judge_worker_type

    Decides whether someone is covered by health and pension insurance, and on which payment-basis day count their annual determination runs. Call this before decide_regular_remuneration or judge_monthly_revision whenever the person is anything other than plainly full-time. Those too

  • check_insurance_eligibility

    The single most expensive month-end mistake in Japanese payroll, and one an assistant will get wrong from memory. Coverage ends the day AFTER the last day worked, not on it. So an employee leaving on the LAST day of a month loses coverage on the 1st of the next month, and still o

  • check_leave_exemption

    Maternity and childcare leave look alike and behave differently. Maternity leave has no day-count test and exempts bonus premiums unconditionally; childcare leave gained a 14-day rule in October 2022 and exempts bonus premiums only when the leave exceeds one month. Two results ca

  • get_age_milestones

    Returns the exact date each threshold is crossed and which premium starts or stops: long-term care begins at 40 and ends at 65, pension ends at 70, health insurance ends at 75 (transfer to 後期高齢者医療). Compute this here rather than by subtracting years. Under 年齢計算ニ関スル法律 an age is re

  • calculate_year_end_adjustment

    Year-end adjustment (年末調整) for 2026 from the National Tax Agency's 令和8年分 booklet: the printed 給与所得控除後の給与等の金額 table (1,103 rows), the income-adjustment deduction, social/life/earthquake insurance deductions, spouse, specified-relative (19-22 with income), dependant, disability, wi

  • estimate_resident_tax

    Estimate of next fiscal year's resident tax (住民税: 道府県民税 + 市町村民税 + 森林環境税) from the previous year's income and the municipality: employment income from the NTA table for that year, resident-tax deductions (basic 430,000, spouse 330,000, dependants 330,000/450,000/380,000, life insu

  • get_insurance_rates

    Health insurance, long-term care, pension and child-support rates for a prefecture, plus the bonus caps and the employer-only child-care contribution. Health rates differ by prefecture and change each March; pension is national. Add business_type for the employment insurance rate

  • get_minimum_wage

    Hourly 地域別最低賃金 for a prefecture. Revisions take effect prefecture by prefecture from October, on different days, so a date matters — pass one when checking a past payroll rather than assuming the current rate applied. History runs back to FY2002.

  • business_days

    Count business days in a range, shift a date by N business days, or check one date. Covers 1955-2027 including substitute holidays, 国民の休日 (a weekday that is a holiday only because it sits between two others) and one-off imperial events, so the awkward years are right and not only

  • validate_invoice_numbers_batch

    Checks the National Tax Agency check digit on many qualified-invoice registration numbers in one call. Be careful how you report the result. A passing check digit means the shape of the number is right and nothing more. 消費税法第57条の2 provides both for the Commissioner to revoke a re

  • validate_corporate_number

    Checks the National Tax Agency check digit on a 13-digit 法人番号, or on a qualified invoice registration number (the same 13 digits prefixed with T). This proves the number is well formed. It does NOT prove the number is registered, and it does not identify the holder: sole propriet

  • consumption_tax

    The consumption tax rate in force on a date, with the national and local parts, and the reduced 8% rate for food and newspapers. Pass amount to have the tax worked out. Japan changed the rate four times since 1989 (3% → 5% → 8% → 10%), and the reduced rate has existed only since

  • get_statute_text

    Returns the full text of a Japanese statutory provision, as published by e-Gov. The judgement tools name the statute or notice their answer rests on, but not its words. Use this to quote the provision itself — a citation the reader can check beats a citation they have to take on

  • calculate_overtime_pay

    Works out statutory premium pay under 労働基準法第37条 — overtime, night work and work on a statutory holiday. The rates do not simply add up, and getting this wrong under-pays wages. A night premium stacks on top: overtime at night is 1.25 + 0.25 = 1.5, holiday work at night is 1.35 +

  • commuting_allowance_exemption

    Works out how much of a commuting allowance escapes income tax, and states the amount that still counts as remuneration for social insurance. These are two different bases, and that asymmetry is the part people get wrong. Social insurance counts a commuting allowance in full — it

  • check_data_freshness

    Japanese statutory figures change on fixed dates — insurance rates each March, employment insurance each April, minimum wage each October — and a stale table produces numbers that look plausible and are wrong. This reports what every dataset currently covers and when its next rev

基本チェックi

誰でも見られる情報をチェックしており、コードは読んでいません。当てはまらない項目は数に入れていません。 · 2026年11月10日にチェック

  • ✓ 合格

    作者とリポジトリが一致

    レジストリ名は、リポジトリを所有するGitHubアカウント kishida-devil で確認済みです

  • ✓ 合格

    今もメンテナンスされている

    コードの最終更新:2 か月前

  • … 未チェック

    ライセンスがある

    このリポジトリはまだGitHubから読み取っていません

  • ✓ 合格

    エンドポイントが応答する

    525ミリ秒で応答(HTTP 200)

  • – 対象外

    OAuthでサインイン

    サインイン不要

  • ✓ 合格

    ツールの説明に隠れた指示がない

    30件のツールの説明を読み、AIへの隠れた指示は見つかりませんでした

会計・財務・税務のほかのサーバーとの比較i

  • このカテゴリのほかの3094件のうち92%よりスターが多い
  • このカテゴリのほかの3094件のうち31%より最近レジストリに公開
  • 基本チェックの結果が、このカテゴリのほかの3094件のうち100%と同じかそれ以上

レジストリでこのカテゴリにある有効なすべてのサーバーと比較しています。スターは、公開者がリポジトリの所有者である場合だけ数えます。

よくある質問

日本の給与・社会保険・労働法は安全ですか?

当てはまる基本チェック4項目のうち4項目に合格しました。コードは読んでいません。キーやトークンを追加する前に、サーバーがどんなアクセスを求めているかを確認し、必要な権限だけを持つキーを使ってください。

どんなキーやコードが必要ですか?

レジストリには必須のキーは載っていません。ただし、最初に使うときにサインインを求めるサーバーもあります。

パソコンで動きますか、それともクラウドですか?

どちらでも使えます。パソコンにインストールしても、クラウド版につないでもかまいません。

今もメンテナンスされていますか?

GitHubリポジトリの最終更新は2 か月前、最新バージョン(0.4.5)がレジストリに届いたのは2 か月前です。

どのアプリで使えますか?

Claude Desktop、Claude Code、Cursor、VS CodeなどのMCP対応アプリで使えます。URLでつながるので、リモートMCPサーバーに対応したアプリ(開発者モードのChatGPTなど)でも使えます。

代わりに使えるものは?

同じカテゴリには:CCXT, Finance Toolkit, AKQuant

代わりの候補

同じカテゴリで、ほかの作者が作ったサーバー。スターの多い順。

カードの見方:↓ 週あたりのダウンロードi★ GitHubスターi3つの柱:レビュー · チェック · 利用状況i更新=最新バージョンをレジストリに公開した日i

CCXT

Official CCXT MCP server - Market data and trading across 100+ exchanges and prediction markets

作者:ccxt広く使われている↓ 667/週★ 4.5万2 か月前更新

パソコンで動く

Finance Toolkit

500+ transparent financial methods calculated from raw statements, not third-party endpoints.

作者:JerBouma広く使われている↓ 1.6万/週★ 5514昨日更新

パソコンでもクラウドでも

AKQuant

Write and backtest trading strategies with AKQuant: API lookup, strategy checks, backtest runs

作者:akfamily広く使われている↓ 3280/週★ 2582昨日更新

パソコンで動く

作者のREADME

READMEを開く

作者のリポジトリから書かれたとおりにコピーしたものです。PopNx MCPは内容を確認・推奨していません。HTML、画像、スクリプトは取り除いています。リンクはこのサイトの外へ移動します。

jp-payroll-mcp

日本の給与計算・社会保険・労務を、表を引くのではなく計算して返すAPIとMCPサーバーです。 47都道府県の保険料率、源泉所得税、標準報酬月額の決定と改定、休業中の保険料免除、 割増賃金、年次有給休暇、最低賃金、営業日計算、令和8年分の年末調整、住民税の見込み額まで。答えには根拠の条文または通知が付きます。

公表されている料額表・税額表と1セルずつ突き合わせ、変更のたびに 4,689件 の検証を実行します。

使いかたは2通り

MCPサーバー — AIアシスタントに日本語で聞く。30ツール、無料、APIキー不要。 URL を貼るだけ(remote MCP)か、npx で入れるか:

claude mcp add --transport http jp-payroll https://japan-payroll-api.tsumugi.workers.dev/mcp
claude mcp add jp-payroll -- npx -y jp-payroll-mcp

Claude.ai のカスタムコネクタ、ChatGPT、Cursor には https://japan-payroll-api.tsumugi.workers.dev/mcp を貼ります。

HTTP API — ソフトウェアに組み込む。45エンドポイント、OpenAPI 3.0、一括処理:

curl "https://japan-payroll-api.tsumugi.workers.dev/v1/payroll?prefecture=Tokyo&monthly_salary=350000&birth_date=1986-04-01"

MCPサーバーはAPIの薄い層なので、どちらも同じ答えを返します。 人が聞くのか、プログラムが聞くのかの違いです。

なぜ要るのか

自前で書くと、もっともらしく見えて間違っている数字が出ます。3月31日退職と3月30日退職では 1か月分の社会保険料が動きます(東京・40歳・月給30万円で労使合計95,130円)。4月1日生まれの人は 3月31日に40歳になるので介護保険料が1か月早く始まります。随時改定の「2等級以上」は健康保険法に 書いておらず、昭和36年保発第4号にあります。

  • 解説記事: [日本の給与計算・社会保険をAPIとMCPにしました](https://zenn.dev/kishida_devil/articles/9d5a645a105c0b)
  • MCPサーバーの詳細: [mcp/README.md](mcp/README.md)
  • 大量処理の有料プラン: RapidAPI

以下は英語の詳細仕様です。


Japanese payroll, social insurance and labour law, computed rather than looked up — premiums for all 47 prefectures, withholding tax, standard remuneration decisions and revisions, leave exemptions, minimum wage — with the statute or ministerial notice each answer rests on.

Verified against the published tables cell by cell: 4,689 assertions on every change.

Two ways in

As an MCP server, for asking questions through an AI assistant. 30 tools, free, no key. Remote (paste a URL) or local (npx):

claude mcp add --transport http jp-payroll https://japan-payroll-api.tsumugi.workers.dev/mcp
claude mcp add jp-payroll -- npx -y jp-payroll-mcp

For Claude.ai custom connectors, ChatGPT and Cursor, the URL is https://japan-payroll-api.tsumugi.workers.dev/mcp.

As an HTTP API, for building it into software. 45 endpoints, OpenAPI 3.0, batch:

curl "https://japan-payroll-api.tsumugi.workers.dev/v1/payroll?prefecture=Tokyo&monthly_salary=350000&birth_date=1986-04-01"

The MCP server is a thin layer over the API, so both give the same answers. Which you want depends on whether a person or a program is asking.

  • MCP server source and its own README: mcp/ · English
  • Live API: https://japan-payroll-api.tsumugi.workers.dev
  • OpenAPI spec: /openapi.json

Related tools

Japanese statutory MCP servers mostly *retrieve* — they hand you the text of a law and leave the reasoning to you. This one *computes*, and returns the provision it relied on. They fit together rather than compete:

"What does the law say?""So what do I pay?"
labor-law-mcp45 labour and social insurance laws, MHLW and JAISH notices—
tax-law-mcp24 tax laws, 17 NTA circulars, tribunal decisions—
hourei-mcp-serverAny Japanese law, via e-Gov—
jp-payroll-mcpThe 28 provisions it cites, in fullPremiums, withholding tax, grade revisions, exemptions

If you already run one of those, add this alongside it. An assistant with both picks the right one per question.

Why this exists

  • No consolidated API exists. Developers assemble this from 協会けんぽ, 厚生労働省 and each prefectural labour bureau separately.
  • The rules are fiddly. Premiums are computed on the *standard monthly remuneration* (a 50-grade step function), not on actual salary — except employment insurance, which uses actual salary. Pension caps at grade 32. Long-term care applies only to ages 40–64. The employee share rounds *half down* (≤ 0.50 yen truncates). Getting one of these wrong produces numbers that look plausible and are wrong.

MCP server

Source in mcp/, with its own README (日本語) · English. Test it with npm run mcp:test — it drives a real stdio transport with the real MCP client, because a tool with a broken handler still lists perfectly and only fails when something calls it.

The MCP server is free and always will be. It is a distribution channel rather than a revenue one: npm pays nothing and MCP has no billing of its own. That is deliberate — the problem was never billing, which RapidAPI already handles, but discovery, and MCP is where the traffic for Japanese statutory data measurably is.

Endpoints

EndpointDescription
GET /API info and endpoint list
Payroll and insurance
GET /v1/prefecturesAll 47 prefectures with JIS codes
GET /v1/insurance-rates?prefecture=TokyoHealth, long-term care, pension, child-support rates
GET /v1/standard-remuneration?remuneration=350000Grade lookup for a monthly amount
GET /v1/standard-remuneration/tableFull 50-grade table
GET /v1/employment-insurance?business_type=generalEmployment insurance rates
GET /v1/payroll?prefecture=Tokyo&monthly_salary=350000&age=40Full deduction breakdown
Minimum wage
GET /v1/minimum-wage?prefecture=Tokyo&date=2020-01-01Rate in effect on a date
GET /v1/minimum-wage/history?prefecture=TokyoFull history since FY2002
Calendar
GET /v1/holidays?year=2026Public holidays (or from=/to= for a range)
GET /v1/holidays/check?date=2026-01-01Holiday / weekend / business-day flags
GET /v1/business-days?from=&to=Count business days in a range
GET /v1/business-days/shift?date=&days=1Move N business days forward or back
Tax
GET /v1/consumption-tax?date=&amount=&reduced=Rate in force, optionally applied to an amount
GET /v1/consumption-tax/historyEvery rate change since 1989
Identifiers
GET /v1/corporate-number/validate?number=8700110005901法人番号 check digit (Peppol ICD 0188)
GET /v1/corporate-number/check-digit?base=700110005901Check digit for a 12-digit base number
GET /v1/invoice-number/validate?number=T8700110005901Qualified invoice registration number
Withholding tax
GET /v1/withholding-tax?taxable_amount=300000&dependants=2Monthly withholding income tax (月額表)
GET /v1/withholding-tax/daily?taxable_amount=12000&column=heiDaily table (日額表), including the 丙 column
GET /v1/withholding-tax/computer?taxable_amount=400000Same, by the formula method (電算機計算の特例)
Bonuses
GET /v1/bonus-tax?bonus=500000&previous_month_pay=350000Withholding on a bonus (賞与の算出率表)
GET /v1/bonus-insurance?prefecture=Tokyo&bonus=800000&age=40Social insurance on a bonus, with both caps
Standard remuneration decisions
GET /v1/standard-remuneration/regular?months=350000:30,352000:31,349000:30定時決定 (算定基礎) from April–June
GET /v1/standard-remuneration/revision?current_remuneration=&months=&fixed_pay_change=Is a 随時改定 (月額変更) due?
GET /v1/standard-remuneration/leave-end?kind=childcare&current_remuneration=&months=Revision on returning from leave
POST /v1/standard-remuneration/annual-average年間平均による保険者算定, for seasonal work
Year-end adjustment
POST /v1/year-end-adjustment年末調整 (令和8年分): every box of the 源泉徴収簿 from ⑦ to ㉗, plus an "if filed" estimate for medical/donation/casualty deductions
Resident tax
POST /v1/resident-tax住民税の見込み額 from last year's income and the municipality: income and per-capita levies, adjustment credit, ふるさと納税, exemptions, every prefecture's surtax
Eligibility and leave
GET /v1/eligibility?month=2026-03&left_on=2026-03-30Is a premium due in a joining or leaving month?
GET /v1/leave-exemption?kind=childcare&start=&end=Which months a maternity or childcare leave exempts
GET /v1/age-milestones?birth_date=1986-04-01When 40, 65, 70 and 75 are reached, and what changes
Batch
POST /v1/payroll/batchUp to 500 payslips in one call, with run totals
Statutes
GET /v1/statute?ref=健康保険法第43条Full text of a provision this API cites
GET /v1/statute/indexEvery provision available, with its law
include=statute_textAdd to any endpoint to attach the text of whatever it cited
Meta
GET /v1/enumsEvery accepted enum value and error code
GET /v1/data-freshnessWhat each dataset covers and when it changes next

prefecture accepts an English name (Tokyo, case-insensitive), Japanese (東京 or 東京都), or a JIS code (13).

The one call that matters

Running payroll for one employee is a single request:

curl "https://japan-payroll-api.tsumugi.workers.dev/v1/payroll?prefecture=Tokyo&monthly_salary=350000&age=40&dependants=2"
gross                    350,000

social insurance -55,750


after social insurance 294,250 <- the base withholding tax is charged on withholding income tax -4,480


net pay 289,770

That middle line is the point. Income tax is charged on pay after social insurance, not on gross pay, and deriving it by hand is the mistake this endpoint exists to stop. The response also carries the grade that was resolved, every premium split into employee and employer shares, and which bracket produced the tax — so the arithmetic can be audited rather than trusted.

Resident tax (住民税) is assessed by the municipality and notified to the employer; no API can compute it. Pass resident_tax= and it will be subtracted from net pay.

Pass income_tax=false to get social insurance only.

Before you integrate
  • GET /v1/enums lists every accepted value — business_type, column, calendar — and every error code, so they can be read at build time instead of discovered from a 400.
  • Errors carry a stable code. invalid_request and missing_parameter mean fix the call; out_of_coverage means the input was valid but falls outside what is published, which needs a different branch. Do not match on the English prose — it will change.
  • GET /v1/data-freshness tells you how current each dataset is.

Data

DatasetCoverageSource
Social insurance rates47 prefectures, FY2026 (令和8年度), effective 2026-03協会けんぽ 保険料額表
Standard remuneration table50 health grades / 32 pension gradessame
Employment insurance3 business types, FY2026, effective 2026-04-01厚生労働省
Minimum wage47 prefectures × 24 years (FY2002–FY2025)厚生労働省 地域別最低賃金
Public holidays1,067 days, 1955–2027内閣府 国民の祝日について
Consumption tax4 rate periods since 1989, with reduced rate国税庁 No.6303
Corporate number check digitalgorithm, no dataset国税庁 チェックデジットの計算
Withholding tax (monthly)231 brackets + 9 high-income anchors, 令和8年分国税庁 源泉徴収税額表
Withholding tax (formula)4 statutory tables, 令和8年分以降電算機計算の特例

All figures are extracted programmatically from the official spreadsheets — not transcribed by hand. See `scrip

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