ARCA
An expense platform where the books can't go out of balance.
One-click demo roles on the sign-in screen.
The problem
Most expense tools are a form glued to a spreadsheet. Money moves, but nothing proves the books still balance. One wrong approval and finance loses a week hunting for a missing cent.
I wanted a system where an unbalanced ledger isn't a bug you catch later. It's impossible.
Three decisions that made it work
The database says no
Every approval posts its journal entry in the same transaction. A deferred constraint trigger checks that each entry sums to zero at commit, so even a buggy service can't write unbalanced books.
DEFERRABLE INITIALLY DEFERRED Three roles, one truth
Employees submit with receipts. Managers approve or reject, and a rejection needs a reason. Admins get analytics, CSV export and the live trial balance. Checked on the API, guarded in Angular.
Receipts never go public
Receipt files only go out through signed links that expire after an hour. A forwarded link dies instead of exposing someone's dinner bill forever.
SELECT COALESCE(SUM(amount), 0), COUNT(*)
INTO v_sum, v_count
FROM journal_lines
WHERE entry_id = v_entry_id;
IF v_count > 0 AND v_sum <> 0 THEN
RAISE EXCEPTION 'Journal entry % is unbalanced: lines sum to % (must be 0)', v_entry_id, v_sum
USING ERRCODE = 'check_violation';
END IF;
...
CREATE CONSTRAINT TRIGGER trg_journal_lines_balanced
AFTER INSERT OR UPDATE OR DELETE ON journal_lines
DEFERRABLE INITIALLY DEFERRED
FOR EACH ROW
EXECUTE FUNCTION arca_check_entry_balanced();Debits are stored as positive amounts and credits as negative ones, so a balanced entry sums to exactly zero. The check waits until commit, which lets both lines land first.
Designed to make money readable
Credit is teal. Debit is coral. You read the state of the books before you read a single number.
Figures sit in IBM Plex Mono with tabular numbers, so columns line up to the cent. On approval, a debit and a credit slide into balance.