# Double Entry Ledger

> Double-Entry Ledger Architecture

- Skill: `j4flmao/double-entry-ledger` (Agent Skill)
- Install (CLI): `npx skillmds@latest add j4flmao/double-entry-ledger`
- Raw SKILL.md: https://api.skillmd.com/api/skills/j4flmao/double-entry-ledger/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: j4flmao (https://skillmd.com/u/j4flmao)
- Updated: 2026-09-21
- Page: https://skillmd.com/skills/j4flmao/double-entry-ledger

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# Double-Entry Ledger Architecture

## Core Mechanics

At the heart of any core banking or FinTech system lies the Double-Entry Ledger. It ensures absolute mathematical consistency: every transaction requires at least two ledger entries (a Debit and a Credit) that must perfectly balance.

### 1. The Accounting Equation
`Assets = Liabilities + Equity`
- **Debit (DR):** Increases an Asset or Expense account. Decreases Liability or Equity.
- **Credit (CR):** Increases a Liability or Equity account. Decreases an Asset.
- **Rule of Zero:** Sum of all Debits - Sum of all Credits MUST equal 0 for every transaction.

### 2. Immutability & Event Sourcing
Ledger entries are Append-Only. You can NEVER update or delete a ledger row. If a mistake is made, a compensating transaction (reversal) must be appended. This guarantees an unforgeable audit trail.

### Double-Entry Flow Map

```mermaid
%%{init: {"theme": "default", "flowchart": {"useMaxWidth": true}}}%%
flowchart TD
    subgraph Transaction ["Transfer $100 from Alice to Bob"]
        A["Validate Sufficient Balance"]
    end
    
    subgraph Ledger ["Immutable Ledger DB"]
        B["Entry 1: DR Alice_Liability $100"]
        C["Entry 2: CR Bob_Liability $100"]
    end
    
    subgraph Validation ["Consistency Check"]
        D{"Sum(DR) == Sum(CR)?"}
    end
    
    A -->|"Begin Tx"| B
    B --> C
    C --> D
    D -->|"Yes (0)"| E["Commit Transaction"]
    D -->|"No (!=0)"| F["Rollback Transaction"]
```