Mouser: Open-Source MX Master 3S Button Remapper Challenges Logitech's Software Monopoly

A new open-source project called Mouser is giving Logitech MX Master 3S owners an alternative to the company's cloud-dependent Options+ software. Developed by Tom Badash, this lightweight tool remaps every programmable button on the popular mouse without requiring a Logitech account or internet connection.

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Local Control Without the Cloud

Mouser takes a fundamentally different approach from Logitech's official software. While Options+ requires users to create accounts, accept telemetry, and maintain internet connectivity, Mouser operates entirely offline. All configuration is stored locally in a JSON file, and the application processes everything on your machine.

The tool supports both Windows and macOS, with the latter added thanks to contributor andrew-sz. The macOS version uses CGEventTap for mouse hooking, Quartz CGEvent for key simulation, and NSWorkspace for application detection.

Complete Button Customization

MX Master 3S owners can remap all six programmable buttons:

• Middle click
• Gesture button
• Back/forward buttons
• Horizontal scroll left/right

Each button can trigger one of 22 built-in actions across navigation, browser, editing, and media categories. Users can also set the mouse to "do nothing" for pass-through functionality.

Per-App Profiles for Power Users

One of Mouser's standout features is per-application profiles. The tool automatically detects when you switch between programs and applies different button mappings accordingly. For example, you might want different bindings for Chrome versus VS Code, or media controls when using VLC.

Profiles are managed through an intuitive Qt Quick interface that shows an interactive diagram of the MX Master 3S. Users click on hotspot dots representing each button to change its action.

Technical Implementation

Mouser uses a sophisticated three-tier detection system for the gesture button:

1. HID++ 2.0 (primary) - Opens Logitech's HID collection and diverts the gesture button using feature 0x1B04
2. Raw Input (fallback) - Detects extra button bits beyond standard mouse inputs
3. Middle-click fallback - Routes middle-click events when the gesture button has an assigned action

For Windows, the tool employs a low-level mouse hook using SetWindowsHookExW with WH_MOUSE_LL to intercept button presses. It also handles device reconnection automatically, detecting when the mouse is turned off or disconnected and restoring functionality without requiring a restart.

Performance and Features

Beyond button remapping, Mouser offers:

• DPI control from 200-8000 with quick presets
• Independent scroll direction inversion for vertical and horizontal scrolling
• Gesture button support over Bluetooth without Logitech software
• Auto-reconnection for power cycles
• Live connection status in the UI
• System tray operation with background running

Installation and Usage

The tool is available as a portable 44 MB download that requires no installation. Users simply extract the zip file and run Mouser.exe. For developers, the source code is available on GitHub with Python 3.10+ requirements.

Download Mouser: Mouser.zip

Source Code: GitHub Repository

The Bigger Picture

Mouser represents a growing trend of open-source alternatives to proprietary hardware software. By providing a free, local, and customizable solution, it challenges Logitech's ecosystem lock-in while maintaining full functionality for MX Master 3S owners.

The project is licensed under MIT and welcomes contributions, particularly for expanding device support beyond the MX Master 3S and improving features like scroll inversion and Linux compatibility.

For users frustrated with Logitech's cloud requirements or those who simply prefer open-source solutions, Mouser offers a compelling alternative that puts control back in the hands of the user.