One Ledger, Four Cron Jobs

Every morning at seven, my phone gets one Telegram message. It lists the bank transactions that landed overnight — a lunch here, an internet bill there — already sorted, already checked against the running balance, and already filed into a ledger I own. If something looks odd, the message asks me about it. Once. If nothing happened, my phone stays silent.

I didn’t build this to be impressive. I built it because I was tired of answering “where did the money go?” from memory.

The system is two small Python skills

The heart is Petasos Finance Vault: an append-only ledger that lives inside my Obsidian vault — one JSON line per transaction, nothing ever overwritten. Around it sits one companion: Petasos Fmarket NAV, which tracks our mutual-fund price every evening. Four cron jobs tie them together — a morning digest, a weekly reconciliation, a monthly close, and the evening price check — plus a handful of plain-text files and rules I can read and edit myself.

The design rule that matters most: the ledger is the only place where numbers live. Everything else — dashboards, monthly reviews, answers to my own questions — is generated from it. When I ask “how much did we spend on groceries?”, the answer comes from the ledger, never from memory.

07:00 — the morning digest

The day starts with the bank. My banks send alert emails for every transaction; a cron job fetches them, parses the amounts, and checks the math: does each new balance actually follow from the previous one? A batched alert, a duplicated email, or a missing credit gets flagged before anything is written. If the chain doesn’t hold, the pipeline appends nothing and tells me why.

Most mornings the digest is five lines. Lunch at the office canteen, 52,000 dong. A coffee stand near the office — 26,000, automatically recognized as coffee because I confirmed that pattern once and it never asked again. The tenant’s rent arriving on the sixth. Each row already carries its category, because a file of rules I maintain maps the merchant names to buckets: food is food, fuel is fuel, a bill payment is never an expense.

Logging life in one line

Cash is where most systems die, so cash gets the most attention. When I buy a coffee for 20,000 dong, I say so in a chat message — “coffee 20k cash” — and it becomes a ledger row immediately, with the drawer balance adjusted in the same step. No receipt-chasing at the end of the month, no “misc” bucket quietly absorbing everything.

When the drawer drifts — it always drifts, because market groceries don’t come with alerts — we count the cash on hand, and the difference becomes one honest line: unlogged cash spending, mostly market runs. Not spread invisibly across a month. One number, on the record.

Some things refuse to be automatic

Not everything can be a pattern. Cash withdrawals from the ATM are re-asked every single time, by design — the one rule that never auto-posts. My wife’s bank sends no email alerts at all, so her salary and her card statement arrive as app screenshots, read and reconciled by hand. And the mortgage is the quietest transaction of all: the bank debits it silently, so each payment is verified by arithmetic — the interest is the remaining principal times the rate times the actual days in the cycle, and if the number doesn’t come out exact, something is wrong.

That last rule has a name in my notes: the app is truth, the books are a hypothesis. When the balance on my phone disagrees with the ledger, the ledger gets investigated — never the phone. More than once this has found a real mistake: an alert that understated a transfer by 88 dong, a card payment that existed in one book but not the other, a mortgage statement that didn’t match its own history by 1.2 million. Small numbers, real errors, all caught because one side refused to be hand-waved.

20:00 — the investments check in

In the evening, a second cron reads the day’s published fund price from Fmarket, appends it to a per-fund series, and evaluates the rules I set for myself: my monthly top-up window, the price levels at which I’ve decided buying more is worth it, the cap beyond which I stop adding. Like the morning digest, it is silent unless something needs me. The alerts arrive on Telegram at dinner time — one line, one decision.

The month closes like a book

On the second of each month — the second, not the first, because stragglers land on day one — a final job checks that every gate is green and no question is unanswered, then freezes the month’s expense total and archives a full snapshot. Closed months can’t quietly change later; if a late correction is ever needed, it happens loudly, with the old total on record.

What it changed

The honest answer is: not the spending. Coffee still costs 20,000 dong. What changed is the friction. Recording money went from a chore I postponed to a sentence I type anyway. Checking it went from a spreadsheet session to a glance. And the questions — “can we afford this?”, “where did last month go?” — stopped being archaeology and started being lookups.

You don’t need my three skills to get there. You need one trusted place where the numbers live, one rule that nothing else gets to overwrite them, and the discipline to let a machine ask you things once instead of wondering about them forever. The cron jobs are just the reminder.