> Usage terms: public: the docs, the `.proto` contract and the example clients; the engine is used under a license and its code is private: build the screens on it, do not recreate it (free licenses for developers, schools and nonprofits: https://stilldeeppos.com/free-program). Full terms and index: https://stilldeeppos.com/llms.txt

# Why StillDeep instead of an AI-generated point of sale

> An AI writes a register screen in an afternoon. StillDeep brings the rest: offline, taxes, security, and 20 years of software, 7 of them in POS.

Source: https://stilldeeppos.com/why-stilldeep

You build the screen, under your brand and with the AI of your choice. StillDeep takes on the risk underneath: the money, the data and the security.

The screen belongs to whoever builds it, the business keeps its server and its data, and the checkout line keeps moving when the Internet goes down because the register keeps selling offline.

## A small error, multiplied by thousands of sales

A demo shows a cart, a total and a receipt. A business lives with what a demo does not show. One rounding error is enough:
- **2 ¢** off per sale
- **300** sales a day
- **$6** missing every day
- **$2,160** a year, for a single register

Add the hours spent finding out why the register does not balance. The same goes for a tax calculated on the wrong amount, a refund counted twice, or a sale lost when the Internet drops in the middle of a payment.

Each of these cases is handled in the StillDeep engine, tested, then rechecked by the business's server: Canadian sales taxes, rounding to 5 ¢ only when everything is paid in cash, shifts that balance to the cent. Registers sell offline and resynchronize without losing or duplicating a sale.

## What an attacker looks for, in the age of AI and bots

A register handles money in a place open to the public, and attackers have AI too now. Bots try every address, every field and every combination of requests, day and night. A rule that only exists in the screen eventually gets bypassed. In StillDeep, the rules live in the engine and the server:

| The attack | What StillDeep does |
|---|---|
| Lowering a price or adding a discount with a forged request | No screen is trusted: the server rechecks quantities, prices, totals and taxes |
| Altering or erasing a sale already made | Every sale leaves the register sealed and chained to the previous one; an altered document is refused |
| Replaying a refund | The server never records the same document twice |
| Reading the database from a stolen register | Registers hold no database password; a lost register is revoked along with its keys |
| Slipping code into an extension | Extensions are signed and verified before they load; if a fingerprint changes, nothing loads |
| Intercepting card numbers | Cards go from the terminal to the processor, never through StillDeep |

Your screen, generated by an AI or written by hand, can change as often as you want: a flaw in the screen gives no access to the database or the sale rules. The details are on the [security page](https://stilldeeppos.com/security.md).

## Three ways to get a register
| | AI screen alone | Closed POS | StillDeep |
|---|---|---|---|
| Offline sales without loss or duplicates | To build | Varies | Included |
| Canadian taxes and cash rounding | To build | Included | Included |
| Rules rechecked by the server | To build | Varies | Included |
| Screen under your brand, in your language | Yes | The vendor's | Yes |
| Data on the business's own server | To build | Varies | Yes |

## What you get

- A proven engine for sales, offline mode, synchronization, Admin, receipts and extensions, built and tested on Windows, Linux and macOS. The [architecture page](https://stilldeeppos.com/architecture.md) shows how it all fits together.
- Dozens of complete, working, production-ready applications (registers, web back offices, online booking and ticketing), grouped by [example business](https://stilldeeppos.com/businesses.md) and provided with their source code to adapt to your business.
- Eleven [modules](https://stilldeeppos.com/modules.md) to combine according to each business's trade.
- A stable contract: your screen connects to the public `stilldeep.v1` contract, in the language of your choice, and stays connected from one version to the next. See [build your screen](https://stilldeeppos.com/developers.md).
- Your data on your own server: the business's server keeps sales and customers, and everything is available in French and English.
- Your time back: you deliver the screen under your brand, fitted to your customer's trade, instead of spending months on taxes, offline mode and security.

## Built by someone who has seen registers in production

StillDeep is designed and built in Quebec by a software engineering graduate who has been programming for over 20 years, including more than 7 building a point of sale before generative AI. [Who builds StillDeep](https://stilldeeppos.com/about.md).
## See it in action
Open an example and make a sale, or start your own screen. [See the example businesses](https://stilldeeppos.com/businesses.md) or [build a register screen](https://stilldeeppos.com/docs/build-a-client.md).