AI skills · updated 2026-10-03

Tax & payroll rule skills for AI – Japan invoice + Germany Midijob 2026

Two skills that compute 2026 rules exactly instead of letting AI guess

Japan: per-date 80%→70% input-tax credit, national ¥106,314 and −¥11,622 against all-80% on the sample. Germany: Midijob 1.000 € employee share 125,33 €, bases 854,06 € / 568,36 €, factor F 0.6619.

The same files run in Claude (claude.ai, Claude Code), ChatGPT Business, Codex and Gemini CLI.

Get it on Whop - $25 onceGet it on Gumroad

jp-invoice-transition-2026

== インボイス経過措置の計算 — 免税事業者等からの課税仕入れ 6件 · 規則 2026.10（2026-10-03 確認）
控除できる仕入税額（国税7.8%分・国税庁 問130 計算方法1）: ¥106,314
参考：消費税等相当額ベース（10/110）: ¥136,300
  80% の期間 2023-10-01〜2026-09-30: 2件 · 支払対価 ¥440,000 → 国税 ¥24,960 · 10/110ベース ¥32,000
  70% の期間 2026-10-01〜2028-09-30: 4件 · 支払対価 ¥1,649,000 → 国税 ¥81,354 · 10/110ベース ¥104,300

de-midijob-2026

== Minijob / Midijob 2026 — 5 Person(en) · Minijob-Grenze 603 € · Übergangsbereich 603,01–2.000 € · Faktor F 0,6619 · Regeln 2026.01 (geprüft 2026-10-03)
Aushilfe Kasse · Brutto 603,00 € · Minijob (gewerblich)
  Arbeitnehmer 21,71 €  (RV 21,71 €)
  Arbeitgeber 187,95 €  (KV 78,39 € · RV 90,45 € · Pauschsteuer 12,06 € · U1 4,82 € · U2 1,33 € · Insolvenzgeldumlage 0,90 €)
  Netto vor Lohnsteuer 581,29 €

What you get

• jp-invoice-transition-2026: Japan's transitional input-tax credit by purchase date, per-supplier cap, small-amount rule
• de-midijob-2026: German Minijob and Midijob social insurance with the 2026 values
• Each with a dated rule table, official sources and the real example output

Install

claude.ai: Customize → Skills → Upload skill (turn on code execution under Capabilities). ChatGPT Business: Skills → Create → Upload. Claude Code: unzip into ~/.claude/skills/. Needs Python 3.8+.

unzip <skill>.zip -d ~/.claude/skills/

What it does not do

Offline – nothing is sent anywhere. Wage-tax withholding and some fund-specific levies are out of scope (each README lists them).

Calculation aids, not tax or payroll advice – have a tax adviser or payroll office confirm.

FAQ

What is a skill?

A folder with a SKILL.md, a script and a dated rule table. Claude (claude.ai, Claude Code), ChatGPT Business, Codex and Gemini CLI load it when your question matches and run the script instead of answering from memory.

How is this different from asking the assistant directly?

Each skill carries a dated rule table and a script, so the assistant computes with the official formula instead of answering from memory.

Does it send my data anywhere?

Offline – nothing is sent anywhere. Wage-tax withholding and some fund-specific levies are out of scope (each README lists them).

How do I install it?

claude.ai: Customize → Skills → Upload skill (turn on code execution under Capabilities). ChatGPT Business: Skills → Create → Upload. Claude Code: unzip into ~/.claude/skills/. Needs Python 3.8+.

What do I get when I buy?

The two zips. On Whop it is in your library as a download lesson with the zip attached; on Gumroad it is the product file.

Is this tax or payroll advice?

Calculation aids, not tax or payroll advice – have a tax adviser or payroll office confirm.