Jp Invoice Check — Development skill for Claude Code

JP Invoice Check

**An Agent Skill, CLI and MCP server that checks a Japanese qualified invoice (適格請求書): the six required items, reduced-rate marks, totals per rate, and the rule that consumption tax is rounded once per invoice per rate.**

Japan's invoice system requires six items on every qualified invoice, and the tax must be rounded once per invoice for each rate, not line by line ([NTA pamphlet](https://www.nta.go.jp/publication/pamph/shohi/shohizei_11.pdf): 「端数処理は一請求書当たり、税率ごとに1回ずつ」). A language model that writes an invoice tends to compute tax per line and add it up. On the example below that gives 597 yen instead of 599 for the 10% items and 285 instead of 286 for the 8% items.

This package computes instead of guessing:

• checks the six items and returns each as true/false (required_items)
• recomputes tax per rate for floor, half-up and ceil rounding (the method is the issuer's choice) and tells you which one the invoice used
• names the per-line rounding mistake (E_TAX_LINE_ROUNDING) separately from other wrong tax
• flags 8% items without a reduced-rate mark, and reduced marks on 10% items
• normalizes the registration number (full-width, hyphens) and checks T + 13 digits and the corporate-number check digit
• reads ISO dates, 2026年10月28日, 令和8年10月28日, and periods

Every message comes in English and Japanese. Python standard library only. No network. MIT.

Use as an Agent Skill

Copy this folder into your skills folder (for Claude: `~/.claude/skills/jp-invoice-check/`). `SKILL.md` tells the agent to put the invoice into JSON and run the checker instead of computing tax itself.

CLI

python -m jpinvoice examples/ok.json                    # exit 0
python -m jpinvoice examples/line_rounding_mistake.json # exit 1, lists the errors
python -m jpinvoice invoice.json --rounding floor       # require one rounding method

from jpinvoice import check_invoice, expected_t