Open Source · MIT · Google Apps Script

Seikyusho

Invoice automation for freelancers and accounting teams.

Built around Japan's qualified invoice and withholding tax rules. No server, no SaaS, no vendor lock-in — just Google Workspace and a single MIT-licensed Apps Script project.

View on GitHub Read the full README

How it works

  1. 1.

    The applicant

    Fills out a multilingual web form (Japanese, English, Traditional Chinese, Spanish) with their invoice details and submits. No account required.

  2. 2.

    The admin

    Gets an email with the PDF already generated. Opens a Google Sheet, picks "Approve" or "Reject". That's it.

  3. 3.

    The system

    Picks the right PDF template (overseas / domestic without withholding / domestic with withholding), assigns a monthly serial number, runs the tax math, sends the notification emails, and files the PDF into Drive.

What's inside

Four-language form

日本語 / English / 繁體中文 / Español, switched via URL parameter. Translation strings live in one file (i18n.html) and are easy to extend.

Qualified Invoice System aware

Toggle a registered invoice issuer number on or off per submission. The PDF layout adapts so a single template covers both pre- and post-October 2023 workflows.

Withholding tax, automated

Handles Japan's 10.21% / 20.42% withholding bands and the ¥1,000,000 threshold. Retroactive: flip a sheet cell from no to yes and the PDF regenerates.

Multi-currency, multi-template

JPY / TWD / USD / EUR out of the box. Three PDF templates: overseas, domestic without withholding, domestic with withholding.

Monthly serial numbering

Format: YYYYMM-NNN (e.g., 202605-001). Counter resets every month, persists in a sheet.

Templated notification emails

Three flows — receipt, approval, rejection — each with editable text and {{INVOICE_NO}} / {{APPLICANT_NAME}} placeholders. PDFs are attached automatically.

Drive-native storage

Every PDF lands in a Drive folder. Easy to share read-only with your accountant or tax filer.

No server, no SaaS

100% Google Apps Script + Sheets + Drive. No external infrastructure to host, monitor, or pay for.

Setup

Two paths in the README: a 20-minute manual copy for anyone new to Apps Script, and a one-command clasp deploy if you already have the toolchain. Either way, you'll need a Google account and one email address for notifications.

Read the full README