All case studies / Custom Products & SaaS

Excel profitability model became a server calculator: one link for managers, PIN-protected admin

Industry: Coffee and tea supplier for businessesScale: sales department, managers using phones and PCsService: End-to-end products and SaaS

4 of 4test cases matched Excel within 0.1%

1 linkphone or PC, nothing to install

3 signalstraffic lights for profitability, profit, and payback

I need something similar

Before

The calculation had to match the client's Excel exactly, which was the main reference
A manager opens one link on a phone or PC and sees traffic lights, profit, and payback
An admin uses a PIN to change cost, leasing, and thresholds, while managers cannot see the cost

What we built

Excel formulas were moved to a Python server engine, each calculation reads the current settings
Matched against Excel with an automated test on four test vectors
PIN-protected admin: cost, leasing, traffic-light thresholds; admin token uses HMAC
The API does not expose cost, equipment prices, or leasing without a token
Mobile-friendly interface in the client's brand colors with their logo, calculation history stored in SQLite

How it works

Managervolumes and sale price

→

Calculation APIFastAPI

→

Engineformulas from Excel

→

Settingscost, leasing, thresholds

→

Resulttraffic lights, profit, payback

Result

Work accepted July 1, 2026
The client approved the look: "visually, I like everything"
Admin changes appear in the next calculation on any device, verified in the browser
The client returned with a new order

Technology

PythonFastAPIuvicornJavaScriptSQLiteCaddysystemd

What matters in a project like this. While settings lived in each device's browser, admin changes did not reach managers. Team-wide values are now stored on the server and read for every calculation.