CCaps Layout Switcher v0.11.0

A lightweight Windows keyboard layout switcher that repurposes the Caps Lock key for quick layout switching with country-specific filtering and configuration persistence.

Features

Caps Lock → Layout Switch: Press Caps Lock to cycle through keyboard layouts
Country Code Filtering: Choose specific layouts to switch between (e.g., English ↔ German)
Shift + Caps Lock → Caps Lock: Hold Shift and press Caps Lock to toggle Caps Lock functionality
Visual Indicator: Scroll Lock LED shows current layout (OFF = English, ON = Non-English)
Verified Switching: Checks that the window actually switched, and falls back to Win+Space in applications that ignore the layout request
Background Mode: Runs silently in the background
Auto-startup: Automatically starts with Windows
Configuration Persistence: Remembers your layout preferences
Low Resource Usage: Minimal CPU and memory footprint
No Dependencies: Single executable file

Installation

Option 1: Install from crates.io (Recommended)

cargo install ccaps

This will download, compile, and install the latest version of CCaps. The executable will be placed in your Cargo bin directory (usually ~/.cargo/bin/ or %USERPROFILE%\.cargo\bin\).

Option 2: Download Pre-built Binary

Download the latest release from the Releases page
Extract ccaps.exe to any folder (e.g., C:\Program Files\CCaps\)
Run the program using command line options

Usage

Command Line Options

# Basic commands
ccaps              # Show interactive menu
ccaps -run         # Run in foreground mode (all layouts)
ccaps -enable      # Save settings + add to auto-startup + start now (all layouts)
ccaps -enable -de  # Same, with English/German
ccaps -disable     # Stop + remove from auto-startup + delete settings
ccaps -start       # Start in background now (saved settings), auto-startup untouched
ccaps -start -de   # Start in background now with English/German (not saved)
ccaps -stop        # Stop background process only (settings and auto-startup kept)
ccaps -status      # Show status and available language codes
ccaps -help        # Show help information
ccaps -v           # Show version information

# Country-specific switching
ccaps -run -de     # English ↔ German switching
ccaps -run -de -fr # German ↔ French switching (no English)

Country Codes

Use ccaps -status to see all available language codes for your system. Common codes include:

Code	Language	Code	Language	Code	Language
`us`	English (US)	`ru`	Russian	`ua`	Ukrainian
`gb`	English (UK)	`de`	German	`fr`	French
`es`	Spanish	`it`	Italian	`pl`	Polish
`pt`	Portuguese	`nl`	Dutch	`cz`	Czech
`jp`	Japanese	`kr`	Korean	`cn`	Chinese

Key Bindings

Key Combination	Action
`Caps Lock`	Switch to next keyboard layout
`Shift + Caps Lock`	Toggle Caps Lock on/off

Visual Indicator

The Scroll Lock LED on your keyboard serves as a layout indicator:

OFF (🔴) = English layout active
ON (🟢) = Non-English layout active

Quick Start Examples

1. Interactive Menu

ccaps

Shows a menu with all available options and current system status.

Available commands in interactive mode:

run - Run in foreground mode (all layouts)
run -de - Run with specific layouts (e.g., English ↔ German)
enable - Save settings, add to auto-startup and start now (all layouts)
enable -de - Same, with specific layouts
disable - Stop, remove from auto-startup and delete settings
start - Start in background now, without touching auto-startup
stop - Stop background process only (settings and auto-startup kept)
status - Show current status and available language codes
help - Show detailed help
menu - Show menu again
exit or e - Exit interactive menu

2. Switch Between English and German

ccaps -run -de

3. Switch Between Multiple Languages

ccaps -run -de -fr -es  # German ↔ French ↔ Spanish

4. Run in Background with English/German, Now and at Every Login

ccaps -enable -de

5. Run in Background Just for Now

ccaps -start       # saved settings (or all layouts)
ccaps -stop        # stop it again; nothing else changes

6. Check Available Languages and Current Configuration

ccaps -status

Output example:

CCaps Layout Switcher Status:
╞══════════════════════════════════════════════════════════════╡
Background process: RUNNING ✓
Auto-startup:       ENABLED ✓
Startup command:    "C:\Program Files\CCaps\ccaps.exe" --background -de
Configuration file: EXISTS ✓
Config path:        C:\Program Files\CCaps\ccaps-config.json
Saved country codes: de

Available keyboard layouts:
┌─────┬──────────────────────────────────────┬─────────────────┐
│ Code│ Language                             │ Status          │
├─────┼──────────────────────────────────────┼─────────────────┤
│ -us │ English (United States)              │ CURRENT ✓       │
│ -ru │ Russian                              │ Available       │
│ -ua │ Ukrainian                            │ Available       │
│ -de │ German                               │ Available       │
└─────┴──────────────────────────────────────┴─────────────────┘

Usage examples:
  ccaps -run            # Run in foreground mode (cycle through all layouts)
  ccaps -run -de        # Switch between English and German
  ccaps -enable -de     # Run in background now and at every login (English/German)
  ccaps -start          # Run in background now, without auto-startup

Status: All systems operational ✓

Configuration Persistence

CCaps saves your layout preferences when you use -enable:

Configuration file: ccaps-config.json (stored in %LOCALAPPDATA%\CCaps\)
Typical location: C:\Users\<username>\AppData\Local\CCaps\ccaps-config.json
Auto-restore: Background process automatically loads saved preferences
JSON format: Human-readable configuration file

Example configuration file:

{
  "country_codes": ["de"],
  "version": "0.11.0"
}

Configuration Management

Saving: ccaps -enable -de saves the English/German preference
Auto-loading: The background process loads saved preferences at login and on ccaps -start
Temporary codes: ccaps -start -de uses English/German this time without saving it
Cleanup: ccaps -disable removes the configuration file; ccaps -stop keeps it
Status check: ccaps -status shows current configuration

How It Works

CCaps uses Windows low-level keyboard hooks to intercept Caps Lock key presses and redirect them to layout switching functionality. The program:

Installs a system-wide keyboard hook
Intercepts Caps Lock key events
Cycles through selected keyboard layouts (filtered by country codes)
Asks the focused window to switch its layout, then checks that it actually did
If the window ignored the request, switches with Win+Space instead (see below)
Updates the Scroll Lock indicator from the layout the window actually has
Blocks the default Caps Lock behavior (unless Shift is held)
Saves and restores layout preferences automatically

Applications That Ignore the Layout Request

Some applications don't handle the standard layout change request, so Caps Lock used to do nothing in them. CCaps now checks the layout after every switch. If it hasn't changed within 150 ms, CCaps presses Win+Space (the Windows layout switch shortcut) and re-reads the layout after each press until the target layout is reached.

In such applications a switch takes about 170–300 ms (depending on how many Win+Space presses are needed) instead of a few milliseconds
Win+Space cycles through all installed layouts, so CCaps may press it several times to reach the next selected one; you may briefly see the intermediate layouts
To avoid switching twice or triggering another shortcut, the fallback is skipped when the window is busy (not responding), when Shift, Ctrl, Alt or Win is held, when you press Caps Lock again, or when another window gets focus

Layout Selection Logic

No country codes: Cycles through all installed layouts
One country code: Switches between English and the specified language
Multiple country codes: Cycles through the specified languages only
English preference: If multiple layouts are specified, English is automatically included unless all specified layouts are non-English

Supported Languages

The layout detection works with all Windows keyboard layouts. The program automatically detects over 40 languages including:

English variants: US, UK, Australia, Canada, New Zealand, Ireland, South Africa
Cyrillic: Russian, Ukrainian, Bulgarian, Serbian, Belarusian
Western European: German, French, Spanish, Italian, Portuguese, Dutch
Nordic: Norwegian, Swedish, Danish, Finnish, Icelandic
Eastern European: Polish, Czech, Hungarian, Slovak, Romanian
Asian: Japanese, Korean, Chinese (Simplified/Traditional), Thai, Vietnamese
Middle Eastern: Arabic, Hebrew, Farsi

Advanced Usage

Background Process Management with Specific Layouts

# Run now and at every login with specific layouts (saved)
ccaps -enable -de         # English/German switching
ccaps -enable -de -fr     # German/French switching
ccaps -enable             # All layouts (default)

# Stop for now / start again; settings and auto-startup are kept
ccaps -stop
ccaps -start

# Remove CCaps from auto-startup and delete its settings
ccaps -disable

Interactive Menu with Configuration

ccaps
# Choose from menu:
# enable -de    # This saves the preference, adds auto-startup and starts in background
# run -de       # This only runs temporarily without saving
# e             # Quick exit from interactive menu

Registry Integration

The program stores startup configuration in:

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
Key: "CCaps Layout Switcher"
Value: "C:\Program Files\CCaps\ccaps.exe" --background -de

Status Monitoring

ccaps -status

Shows:

Background process status
Auto-startup configuration
Configuration file status and location
Saved country codes
All available keyboard layouts with country codes
Current active layout
Usage examples and recommendations

Building from Source

Prerequisites

Rust 1.70 or later
Windows 10/11
Visual Studio Build Tools (for linking)

Build Steps

git clone https://github.com/holgertkey/ccaps.git
cd ccaps
cargo build --release

The executable will be created at target/release/ccaps.exe.

Dependencies

winapi: Windows API bindings
ctrlc: Ctrl+C signal handling
serde: Serialization framework
serde_json: JSON serialization

Technical Details

Language: Rust
Version: 0.11.0
Windows APIs: WinAPI (winuser, winreg, synchapi, fileapi)
Hook Type: Low-level keyboard hook (WH_KEYBOARD_LL)
Registry: Uses HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
Configuration: JSON file in %LOCALAPPDATA%\CCaps\
Mutex: Global mutex prevents multiple instances
Layout Detection: Language ID extraction from HKL handles

Diagnostics in Foreground Mode

ccaps -run prints a line for every Caps Lock press, which helps to find applications where switching doesn't work as expected:

[10:42:13.517] us → ru  Switched: 6 ms · firefox.exe (MozillaWindowClass)
[10:42:15.004] ru → us  SwitchedByFallback: 2× Win+Space, 231 ms · Code.exe (Chrome_WidgetWin_1)
[10:42:16.100] us → ru  Switched late: applied after the 150 ms check, no Win+Space, 180 ms · idea64.exe (SunAwtFrame)
[10:42:17.250] us → ru  Failed: a modifier key is held, no Win+Space, 151 ms · app.exe (AppWindow) (+2 earlier press(es) skipped)
[10:43:01.002] Layout ru in Telegram.exe (Qt51517QWindowIcon), not switched by CCaps → Scroll Lock ON

Each line shows the time, the layouts, the outcome with its reason, how long the switch took, and the application (executable and window class):

Switched: the window applied the layout request
Switched late: the window applied it after the 150 ms check, so no Win+Space was needed (the application was busy)
SwitchedByFallback: the window ignored the request; the layout was reached with Win+Space
Unverified: CCaps can't tell whether the layout changed (e.g. the window isn't responding)
Failed: the layout was not changed; the reason says why
earlier press(es) skipped: rapid presses were merged, only the last one was carried out
not switched by CCaps: the layout changed in another way (Win+Space, the mouse, another window got focus) and the Scroll Lock indicator followed it

Known Limitations

Windows running as administrator: when an elevated window (e.g. cmd or regedit started "as administrator") has focus, Windows doesn't pass keyboard input to CCaps, which runs with normal rights. In such windows Caps Lock works as a regular Caps Lock and doesn't switch the layout. Switch the layout with Win+Space there.
Terminals that control Scroll Lock (mintty: Cygwin, MSYS2, Git Bash): mintty resets the Scroll Lock LED itself, so the indicator doesn't reflect the layout while a mintty window has focus. Layout switching works normally.
Applications that ignore the layout request: switched with Win+Space (see Applications That Ignore the Layout Request), which is slightly slower.

Troubleshooting

Caps Lock toggles Caps Lock in some windows

The window is probably running as administrator; see Known Limitations.

The Scroll Lock indicator doesn't match the layout

In mintty-based terminals (Cygwin, MSYS2, Git Bash) this is expected; see Known Limitations
Elsewhere the indicator follows the actual layout within a quarter of a second, also after switching with Win+Space or the mouse

Invalid Country Code Error

ccaps -run -zz
# Error: Unknown country codes: zz. Use 'ccaps -status' to see available codes.

Solution: Run ccaps -status to see all available country codes for your system.

Program doesn't start with Windows

# Check status
ccaps -status

# Re-enable startup
ccaps -enable -de   # or your preferred layout codes

Configuration not loading

Check if configuration file exists: ccaps -status
Restart background process: ccaps -stop then ccaps -start
Delete and recreate: ccaps -disable then ccaps -enable -de

Layout switching not working with specific codes

Ensure the specified keyboard layouts are installed in Windows
Check available codes with: ccaps -status
Verify layouts in Settings → Time & Language → Language → Preferred languages

Uninstall

# Stop the program and remove all traces
ccaps -disable

# Delete the executable file
del ccaps.exe

# Configuration file is automatically deleted by 'ccaps -disable'

License

This project is licensed under the MIT License - see the LICENSE file for details.

Changelog

See CHANGELOG.md for the full version history.

Name		Name	Last commit message	Last commit date
.github/workflows		.github/workflows
src		src
.gitignore		.gitignore
CHANGELOG.md		CHANGELOG.md
Cargo.lock		Cargo.lock
Cargo.toml		Cargo.toml
LICENSE		LICENSE
README.md		README.md
build.rs		build.rs

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