When two AI agents pay each other, who audits the money? I gave them a 500-year-old answer.

When two AI agents pay each other, who audits the money? I gave them a 500-year-old answer: double-entry bookkeeping.

Agentic payments are coming fast, and the hype skips the boring question. How do you know the books are right when no human is in the loop? An agent that moves value needs the same accounting rigor as a bank, minus the human who used to catch the mistakes.

So my account-to-account payments engine records every movement as a balanced double-entry ledger entry in integer minor units. Debits equal credits, or the entry doesn't exist. Reconciliation stops being a nightly batch job that hopes the numbers agree. It becomes a property the write path enforces on every transaction.

On top of that sits a rail-agnostic design. The same core drives a real settlement rail and a simulated one for testing, and webhooks are signed so a forged "you got paid" message can't fool the ledger.

Here's the lesson I keep coming back to. New technology doesn't excuse you from old correctness. Agents are new. The requirement that money balances is as old as commerce.

If you're building anything where software moves value on its own, ask me how I structured the ledger. It's the part that keeps you solvent.