ModSwitchIME

Instantly switch IMEs with 8 modifier keys - A macOS app for multilingual users

Overview

ModSwitchIME is a macOS menu bar application that allows you to instantly switch to any IME by simply pressing a modifier key (Command, Shift, Control, Option) alone.

Perfect for

• 🌐 Multilingual developers - Code in English, comment in your native language
• 📝 Translators & Writers - Quick switching between source and target languages
• 🎯 Anyone seeking a simple, IME-switching focused tool

Features

1. IME Switching with Modifier Keys

Freely assign any IME to all 8 modifier keys

• Left/Right Command ⌘
• Left/Right Shift ⇧
• Left/Right Control ⌃
• Left/Right Option ⌥

Assign your preferred IME to each key. For example:

• Left Command → English
• Right Command → Japanese
• Left Shift → Chinese
• Any system-registered IME can be configured

How it works

• Single key press: Press and release modifier key alone → Switch to assigned IME
• Multi-key press: Press multiple modifier keys → Switch to the IME of the last pressed key
• Normal shortcuts: Modifier key + other keys → Standard shortcuts work as usual (Cmd+C, Cmd+V, etc.)
• Left/Right distinction: Treats left and right modifier keys as separate keys
• Instant switching: IME switches immediately upon key release (no delay needed)

2. Advanced IME Switching Features

Multi-Key Press

When multiple modifier keys are configured with IMEs:

• Switches to the IME of the last pressed key during simultaneous press
• Example: Left Cmd (English) + Right Cmd (Japanese) → Switches to Japanese

Smart Detection

• Distinguishes between single key press and key combinations
• Helps prevent accidental switching during shortcuts (Cmd+W, Ctrl+Tab, etc.)
• Designed to work with your existing keyboard shortcuts
• Note: Detection is based on modifier key events only

3. Auto-Switch on Idle

Settings

• Enable/Disable: Toggle switch
• Idle detection time: 1-300 seconds (1-second increments)
• Target IME:
  • Default: English (ABC)
  • Customizable: Any system-enabled IME

Behavior

• Counts time without keyboard activity
• Automatically switches to specified IME when idle time is reached
• Does not detect mouse activity (keyboard only)
• Returns to normal operation on key input

4. Real-time Settings Update

• Most settings apply instantly without app restart
• Real-time changeable settings:
  • IME assignments to modifier keys
  • Auto-switch on idle toggle
  • Idle time modification
  • Target IME selection
• Note: Some system-level changes may require menu bar icon click to refresh

5. Performance Characteristics

• Startup time: Fast application launch
• IME switch speed: Fast switching with 50ms duplicate prevention
• CPU usage: Low resource usage when idle
• Memory usage: Lightweight memory footprint
• Battery impact: Minimal

6. Enhanced Stability & Recovery

Automatic System Recovery

• Event tap health monitoring: Monitors system-level key detection capability
• Automatic recovery: Attempts to restore functionality when macOS disables key monitoring
• Duplicate prevention: 50ms throttling prevents accidental duplicate switches
• Application focus tracking: Detects IME state changes when switching between applications
• Background resilience: Designed for stable operation during system activity

Reliability Features

• Automatic recovery: Attempts to restore functionality without user intervention
• System integration: Handles macOS updates and permission changes gracefully
• Performance optimization: Reduces redundant operations while maintaining responsiveness

Security & Privacy

ModSwitchIME is designed with privacy and security as core principles:

• Privacy-first design: Detects key presses to distinguish shortcuts from single modifier keys, never captures text content
• No data collection: All processing happens locally on your Mac
• Open source: Complete source code available for inspection
• Code signed: Official releases are signed with Developer ID and notarized by Apple

📋 View detailed Security Policy

Installation

System Requirements

• macOS 13.0 (Ventura) or later
• Accessibility permission required

Installation Steps

1. Download the latest DMG from Releases
2. If updating: Quit ModSwitchIME first (click 🌐 icon → Quit)
3. Mount the DMG and drag ModSwitchIME.app to Applications folder
4. Grant accessibility permission on first launch

Note: When updating, you must quit the app first to avoid "Item is in use" error. This is a macOS security feature.

Usage

Basic Setup

1. Click the "🌐" icon in menu bar
2. Select "Preferences..."
3. Assign desired IMEs to each modifier key

Settings

Modifier Key Assignment

• Assign IME to each of 8 modifier keys
• Default: No automatic assignments (manual configuration required)

Switching Behavior

• Instant switching: IME switches immediately when you release a modifier key
• No delay required: Unlike other tools, no waiting time needed
• Smart detection: Automatically distinguishes between single key press and shortcuts

Auto-Switch on Idle

• Idle time: 1-300 seconds
• Target: Select any IME

Technical Comparison with Other IME Switchers

Implementation Approaches

ModSwitchIME uses TISInputSource API for direct IME switching, while most other apps use key event simulation:

App	Implementation	Strengths	Limitations
ModSwitchIME	TISInputSource API with retry	Direct IME control, reliable CJK support	Requires accessibility permission
英かな (eisukana)	CGEvent API + TIS	Simple, lightweight	Primarily English⇔Japanese
Karabiner-Elements	IOKit HID interception	Highly customizable, low-level control	Known CJK switching issues
BetterTouchTool	Automation/External tools	Wide gesture support	Indirect, requires helper tools
Hammerspoon	Lua scripting bridge	Unlimited customization	Requires programming knowledge

Key Technical Advantages

1. Direct IME Control

• ModSwitchIME: Uses TISSelectInputSource for immediate switching
• Others: Most simulate Cmd+Space or send key codes (indirect method)

2. CJK Language Reliability

• ModSwitchIME: Implements retry logic and verification for reliable CJK switching
• Karabiner-Elements: Documented issues with TISSelectInputSource for CJK languages
• Others: Inherit macOS API limitations or use workarounds

3. Modifier Key Support

• ModSwitchIME: All 8 modifier keys (Left/Right × 4) independently configurable
• 英かな: Left/Right Command only
• Others: Various key combinations, often require complex configuration

4. Configuration Complexity

• ModSwitchIME: GUI-based configuration
• Karabiner-Elements: JSON file editing required
• Hammerspoon: Lua programming required
• Others: App-specific interfaces

Why Choose ModSwitchIME

For users who need:

1. Reliable multilingual switching - Especially for CJK languages
2. Maximum modifier key flexibility - 8 independent keys vs 2-4 in other apps
3. Fast switching - Direct API calls (50ms duplicate prevention)
4. Simple configuration - GUI vs JSON/programming
5. IME-focused design - Purpose-built vs general automation tools

Technical uniqueness:

• Only app using modern TISInputSource API for comprehensive IME control
• Precise modifier key detection for single key vs combination
• State-based implementation for reliable key detection

Troubleshooting

IME not switching

1. Enable ModSwitchIME in System Settings → Privacy & Security → Accessibility
2. The app automatically detects and recovers from system permission issues
3. If issues persist, restart the app - it will automatically restore full functionality

System Updates or Permission Changes

ModSwitchIME includes automatic recovery features:

• Automatic detection: Monitors system permission status continuously
• Self-healing: Automatically restores functionality after macOS updates
• No manual intervention: Recovery happens in the background without user action

License

MIT License

Copyright © 2025 nissy. All rights reserved.