Kassenwart

A local club I volunteer for was tracking [[180]] members and their annual dues in a spreadsheet that three people edited by hand. Every year the treasurer spent an evening cross-referencing bank statements against a members list, chasing the ones that did not match.

Kassenwart replaced that evening with about ten minutes.

Built around one job#

The tool does one thing well: it reconciles incoming payments against member dues, automatically.

Swiss invoices carry a QR-bill with a structured reference number. Banks export statements as CAMT.053 XML, which includes that reference on every transaction. Match the two and reconciliation is a lookup rather than a search.

/// Matches a bank transaction to an invoice by its structured reference.
/// Falls back to nothing on purpose — a wrong automatic match is far worse
/// than asking the treasurer to resolve it by hand.
export function matchTransaction(
  tx: BankTransaction,
  invoices: Map<string, Invoice>,
): Invoice | null {
  const reference = normaliseReference(tx.reference);
  const invoice = invoices.get(reference);
 
  if (!invoice) return null;
  if (invoice.amountCents !== tx.amountCents) return null;
 
  return invoice;
}

That deliberate refusal to guess turned out to be the most important decision in the project. An early version matched on amount plus approximate name, and the first partial-payment case assigned money to the wrong family.

Building for non-technical users#

The people using this are volunteers, not staff. Several are well past retirement age, and the tool had to survive being handed to a new treasurer every couple of years.

• No jargon anywhere. The interface says "Not yet paid", never "Unreconciled".
• Everything reversible. Every automatic match can be undone with one click.
• Printable. The committee wanted paper for the AGM, so every view prints properly.
• One page of documentation. If it needed more, I treated that as a design bug.

Why it is archived#

The club merged with a neighbouring one in [[mid-2025]] and moved to the larger club's existing platform. I handed over the data, exported everything to CSV, and shut the instance down.

That is the honest outcome, and I would rather show it than pretend otherwise. It ran in production for [[16 months]], handled [[roughly CHF 40,000]] in dues across two billing cycles, and lost nothing.

What I learned#

• Talk to the actual user, repeatedly. My first prototype solved the problem I imagined the treasurer had. Watching her work for an hour changed the design.
• Refusing to guess is a feature. The version that matched aggressively was worse than the one that asked for help.
• Handover is part of the job. Because I had planned the export path from the start, shutting it down took an afternoon instead of a crisis.