Mission Planner is a desktop application used for planning and executing autonomous missions for unmanned systems built on ArduPilot. While functional, it requires local installation and operates independently of existing operational platforms. This thesis presents the design and implementation of a web-based mission planning interface for an Unmanned Surface Vehicle, an autonomous water surface vehicle developed by Aquality, which communicates via the Micro Air Vehicle Link protocol. The interface replaces Mission Planner with a browser-based alternative, accessible within Aquality's existing platform, and requires no local installation. The system provides interactive mission planning through a Leaflet.js map interface, supporting manual waypoint placement, automated lawnmower coverage path generation with no-go zone avoidance, shore margin configuration, and pathfinding for return navigation. Communication with the autopilot is handled via mavlink2rest, enabling mission upload, mode switching, arming and disarming, and live telemetry display. Missions can be saved, loaded, edited, and deleted as files on the onboard Raspberry Pi. The system was validated through simulation, bench testing, and field testing at a settling pond in Halmstad. Mission upload was completed in an average of 0.22 seconds for 118 waypoints, compared to approximately 31.4 seconds for Mission Planner. The developed interface demonstrated functional parity with Mission Planner for Aquality's operational requirements, eliminating the need to switch between separate systems for mission planning and data analysis.