CapsLock Layout Switcher

A lightweight system tray utility for Windows 10/11 that turns the Caps Lock key into a keyboard layout switcher.

No more awkward Alt+Shift or Win+Space finger gymnastics. One tap on Caps Lock — the language changes instantly. And because the physical Caps Lock behavior is suppressed, you will never accidentally type in ALL CAPS again.

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Table of Contents

• Features
• Quick Start
  • Option 1: Ready-made executable
  • Option 2: Build from source
• How It Works
  • Layout switching
  • Caps Lock suppression
  • Single-instance guard
• Configuration
• Requirements
• License & Distribution
• Feedback

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Features

Feature	Description
Instant layout switching	Tap Caps Lock to cycle through all installed keyboard layouts.
Caps Lock suppression	The LED never turns on; your text stays lowercase.
System-native mechanism	Uses the same Windows API as Alt+Shift, works in every app.
Single-instance guard	Prevents accidental duplicate launches with a friendly dialog.
System tray icon	Blue "CL" icon with a menu to copy source or exit.
Alt+Shift emulation mode	Optional: emulate physical Alt+Shift instead of Windows API (toggle via tray menu).
Self-contained .exe	No Python, no dependencies, no installation.
Open source	Public domain — use freely for any purpose.

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Quick Start

Option 1: Ready-made executable

1. Download capslock_layout_switcher.exe from the Releases page.
2. Double-click to run. No installation, no Python, no dependencies.
3. (Optional) Place it in your autostart folder for automatic launch on login:

   Win+R → shell:startup
   

4. Press Caps Lock to switch languages.

Option 2: Build from source

Requires Python 3.x and pip.

pip install pyinstaller
python capslock_layout_switcher.py   # auto-generates icon.ico
pyinstaller --onefile --noconsole --icon=icon.ico --add-data "capslock_layout_switcher.py;." capslock_layout_switcher.py

The .exe will appear in the dist/ folder.

Note: --onefile bundles everything into a single self-contained executable. On launch it briefly unpacks to a temporary folder — this is normal pyinstaller behavior and shows two processes in Task Manager until the app closes.

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How It Works

Layout switching

The program installs a low-level keyboard hook (WH_KEYBOARD_LL). When Caps Lock is pressed, it either:

• Emulates Alt+Shift (default) — synthesizes physical keypresses just like you pressed the real keys. Works reliably even when the Windows API method fails.
• Uses Windows API — sends a WM_INPUTLANGCHANGEREQUEST message to the foreground window. This is the same mechanism Windows uses when you click the language bar.

Toggle between the two modes from the tray icon menu: Emulate Alt+Shift.

The program queries the list of installed layouts at runtime via GetKeyboardLayoutList. If you have 2 layouts, it toggles between them. If you have 5, it cycles through all 5 in order.

Caps Lock suppression

After switching the layout, the program checks the Caps Lock state. If it is on, it synthesizes a key-release event to turn it off immediately. The LED stays dark and your case stays normal.

Single-instance guard

On launch, the program creates a named system mutex (CapsLockSwitcher_Mutex_7A3F). If another instance already holds it, a top-most dialog appears:

"CapsLock Switcher is already running. Do you want to terminate it?"

• Yes — signals the running instance to close. The new instance does not start.
• No — leaves the running instance alone. The new instance still does not start.

This works reliably regardless of whether the tray icon is enabled or not.

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Configuration

Open capslock_layout_switcher.py in any text editor. Three flags near the top control behavior:

ENABLE_LOGGING = 0      # 1 = write capslock_switcher.log next to the .exe
ENABLE_TRAY_ICON = 1    # 0 = run completely silent, no tray icon
EMULATE_ALT_SHIFT = 1   # 1 = emulate Alt+Shift keypress, 0 = use Windows API

Flag	0	1
ENABLE_LOGGING	No log file created	Debug log written to application folder
ENABLE_TRAY_ICON	No tray icon, no menu	Tray icon with right-click menu
EMULATE_ALT_SHIFT	Use Windows API (WM_INPUTLANGCHANGEREQUEST)	Emulate physical Alt+Shift keypress

Changes take effect the next time you run the program.

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Requirements

• Windows 10 or Windows 11
• For building from source: Python 3.x + pip + pyinstaller

The released .exe is fully self-contained and does not require Python on the target machine.

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License & Distribution

This project is released into the public domain.

You may use, copy, modify, distribute, bundle, sell, or do absolutely anything with the source code and the compiled binary — no attribution required, no restrictions apply.

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Feedback

Suggestions, bug reports, and pull requests are welcome.

If this tool saved you a few awkward key combinations, feel free to star the repository.