OpenTax

OpenTax is a free, open-source accounting software for individual business owners in Japan.

You can connect it to AI agents that support MCP, such as Claude, ChatGPT, Claude Code, and Codex. You can pass bank statements and receipts to AI to streamline bookkeeping, organize supporting documents, and draft invoices all at once.

What You Can Do

• Register, confirm, and manage double-entry bookkeeping journal entries and their history
• Manage clients, projects, quotations, invoices, and receipts
• Store supporting documents and manage fixed assets
• Generate profit and loss statements, balance sheets, tax amount previews, and output files for e-Tax

The system works by having AI read and judge, while OpenTax verifies and records. Journal entries registered by AI enter a "pending confirmation" status, and you can finalize them after reviewing the content. Accounting and tax calculations are performed not by AI, but by code with fixed rules.

Source code is published under AGPL-3.0. You can run it in your own environment, and data can be stored in your own Firebase. OpenTax itself is free (costs for your operating environment and AI services are separate).

Currently in preview version. Please verify the contents of your ledgers and tax filings yourself.

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