NF525: What a Till Must Guarantee, and Why AI Should Care

When people ask me what a real audit trail looks like, I bring up a French fiscal standard. It usually gets a strange look.

NF525 is the certification that applies to point-of-sale software in France. Working under it was not glamorous, and it was the best training I know for what I do now.

Four words

The standard exists to prevent VAT fraud, and it rests on four requirements: inalterability, security, retention and archiving. In practice they reshape the whole product.

You cannot edit a recorded sale. A correction is a new event, visible next to the original, and it leaves no gap in the numbering. Each action records who did it, when, on what, and why. The history is not a convenience for the support team. It is the product's contract with the outside world.

The details that decide

The rules become very concrete. The till checks that past closures were done before it allows a new sale. A cancellation requires a reason. A reprint has to say so, with a copy number. A discount on a whole receipt has to be spread across items and VAT rates, and a rule has to decide where the last rounding cent goes.

Once you have designed software under those constraints, you stop thinking of logs as a developer tool.

Why this goes beyond tills

Look at how most software records what happened. It is good for debugging, and it does not help when someone asks a harder question: who changed this, on whose authority, and what did it say before?

That question is coming to every company putting automated systems to work. The fiscal mindset adds one more thing: an unrecorded failure is worse than a failure. A till that loses a transaction and shows nothing is far more dangerous than one that shows an error.

Design the record for the person who will question it, not for the person who debugs it.