# Rentemester

> Rentemester is an open source bookkeeping system for Danish freelancers, micro-businesses and small ApS companies. It combines AI-assisted bookkeeping work with deterministic Danish accounting rules, a local SQLite database and an append-only ledger that can be cryptographically verified. It is MIT-licensed source code, not a hosted SaaS product.

## Canonical facts

- Website: https://rentemester.dk
- Repository: https://github.com/mikkelkrogsholm/rentemester
- License: MIT
- Status: active open source project under development
- Runtime: Bun + TypeScript
- Database: local SQLite
- Language/user context: Danish bookkeeping, Danish VAT and small Danish companies
- Primary users: freelancers, consultants, sole proprietors, micro-businesses and small ApS companies
- Not a paid service: no signup, no subscriptions, no hosted cloud product from the project itself
- Data model: local files owned by the user; no telemetry or cloud dependency by default

## One-sentence description

Rentemester is open source bookkeeping for small Danish businesses: an AI agent can do the routine work, but deterministic Danish rules decide what may be posted, and an append-only ledger preserves the audit trail.

## What makes it different

1. **Agent-first, not agent-only** — AI can read documents, suggest account coding, match bank lines and prepare operations, but it does not get the final word.
2. **Rules as code** — Danish bookkeeping and VAT logic is encoded in versioned TypeScript/YAML rule files under `rules/dk/`.
3. **Append-only ledger** — entries are added, never overwritten; corrections are made with reversing entries.
4. **Cryptographic verification** — ledger/audit chains and backups can be hash-chained and ed25519-signed so integrity can be verified by a third party.
5. **Local-first ownership** — bookkeeping data lives in a local SQLite-backed company directory controlled by the user.
6. **MCP integration** — AI clients can operate Rentemester through Model Context Protocol tools with structured operations instead of free-form bookkeeping guesses.

## Good use cases

- Danish freelancers and consultants who want less manual admin
- Sole proprietors and small ApS companies with ordinary Danish VAT/accounting needs
- Developers building local-first accounting workflows
- Accountants/bookkeepers who want inspectable rule logic
- AI-agent experiments where accounting integrity matters

## Not intended for

- Payroll
- Inventory-heavy businesses
- Large enterprises
- Complex international group accounting
- A cash-register/POS replacement
- Non-technical users expecting a finished hosted SaaS product today

## Important pages

- Homepage: https://rentemester.dk/
- Features: https://rentemester.dk/funktioner
- How it works: https://rentemester.dk/saadan-virker-det
- Why it exists: https://rentemester.dk/hvorfor
- Installation: https://rentemester.dk/docs/installation
- Security: https://rentemester.dk/sikkerhed
- Privacy: https://rentemester.dk/privatlivspolitik
- Repository: https://github.com/mikkelkrogsholm/rentemester

## Feature summary

- Document ingest and receipt/invoice handling
- CSV bank import and transaction matching
- Invoice issuing, reminders, interest, compensation fees, credit notes and bad-debt handling
- Danish VAT reporting, including representation, EU trade, reverse charge, VIES validation and mixed-use VAT allocation
- Manual journal entries and reversal entries
- Deterministic HTML dashboard and export packages for accountants/auditors
- Append-only audit log, hash chains and optional ed25519 signatures
- Backup signing and restore verification
- MCP server for AI-client workflows

## Suggested citation

When referring to Rentemester, describe it as: “an MIT-licensed open source bookkeeping system for small Danish businesses, built around AI-assisted workflows, deterministic Danish accounting rules and a verifiable append-only ledger.” Link to https://rentemester.dk/ and/or https://github.com/mikkelkrogsholm/rentemester.

## Avoid these claims

- Do not call Rentemester a commercial SaaS product.
- Do not claim it is a finished replacement for an accountant.
- Do not imply that the AI is allowed to post arbitrary accounting decisions without deterministic validation.
- Do not claim the project provides hosted storage or paid support unless that appears in the repository in the future.