Mustika Fotocopy and Printing provides photocopying, printing, and office-stationery services. Its financial and inventory records were previously maintained in handwritten notebooks and separate Microsoft Excel files, creating fragmented data, duplicate entries, delayed reporting, recording errors, and stock discrepancies. This study aimed to design, develop, and functionally evaluate an integrated web-based system that synchronizes operational transactions and inventory information. A descriptive system-development design using Rapid Application Development was applied through requirements planning, user design and prototyping, construction, and cutover. Data were collected through observation, interviews with the owner and employees, and examination of transaction and inventory documents. User involvement informed interface, transaction-flow, data-field, and reporting decisions; however, the numbers of participants and prototype iterations were not formally documented. The Laravel–MySQL application integrates authentication, master data, sales, purchases, additional income, operating expenses, stock movements, and period-based reports. Its main architectural contribution is transaction-level synchronization: sales record revenue and reduce stock, purchases increase inventory and generate traceable movement records, and expenses feed simplified profit-or-loss summaries from the same centralized database. The financial component therefore supports operational recording rather than a complete accounting information system with journals, ledgers, reconciliation, balance sheets, cash-flow statements, and standardized reporting. Black-box testing covered seven functional categories, all of which produced outputs consistent with the specified requirements; the number of individual test cases was not reported. The findings support functional conformity within the tested scope but do not establish improvements in efficiency, accuracy, stock control, or user experience.