[jrgv]

YNAB is double-entry but not the way you would normally do it (note, I have no idea how it is implemented under the hood, I'm just referring to how I explain YNAB's system to myself). YNAB essentially puts your accounts (assets and liabilities) on one side of the balance sheet and the budgets on the other. It is double-entry in the sense that every transaction is either between two accounts, or between an account and a category (a budget account), so there are two sides to every transaction.

However, in "normal" double-entry accounting, you would not have assets and liabilities on the same side of the balance sheet, and the way YNAB does this leads to some strange behavior. For example, if your net wealth (assets and liabilities) is negative, you need a negative budget ("pre-YNAB debt"). So now you have in your budget both money you plan to spend on actual expenses, and debt.

You could, in principle, design a YNAB-like double-entry accounting system where your assets balance against equity and debt, and where the money that is "available to budget" matches the actual money you have available, regardless of whether that money originates from equity or debt. That would be closer to the normal understanding of double-entry accounting.