If a custom keyboard shortcut doesn’t behave as expected, the issue is usually not a bug — it’s a limitation imposed by the operating system or standard application behavior.

This guide explains why certain shortcuts are restricted and how to choose combinations that work reliably across macOS and Windows.

Why Some Keyboard Shortcuts Are Not Allowed

Some key combinations are reserved by the operating system or widely used by other applications. Allowing these shortcuts would lead to unreliable behavior, conflicts, or shortcuts that fail silently.

To prevent this, we apply validation rules to ensure every shortcut is:

  • Technically reliable
  • Free from system-level conflicts
  • Consistent across platforms

macOS

For best compatibility on macOS, we recommend:

  • Fn (on built-in Mac keyboards)
  • Ctrl + Option or Option + Command (for external keyboards)
  • Right-side modifier keys (Right Command or Right Option)
  • Less commonly used keys such as Page Up

Windows

On Windows, the following combinations generally work well:

  • Ctrl + Windows or Ctrl + Alt
  • Right-side modifier keys (Right Ctrl or Right Alt)
  • Rarely used keys such as Page Up

Shortcut Validation Rules

✅ Supported Shortcuts

A shortcut is valid if it:

  • Uses no more than three keys
  • Includes at least one modifier or non-alphanumeric key
  • Uses either left or right modifiers, but not both
  • Does not conflict with system or application shortcuts

❌ Unsupported Shortcuts

A shortcut will be rejected if it:

  • Is already in use
  • Conflicts with system-level shortcuts
  • Uses only letters or numbers
  • Uses more than three keys
  • Mixes left and right versions of the same modifier

System-Reserved Shortcuts

macOS Reserved Shortcuts

Commonly blocked shortcuts include:

  • Command-based actions (Copy, Paste, Quit, Save, etc.)
  • Navigation shortcuts using Command + Arrow keys
  • Spotlight and screenshot shortcuts
  • System-level commands such as Force Quit and Logout

Windows Reserved Shortcuts

Blocked shortcuts include:

  • Common Ctrl-based shortcuts (Copy, Paste, Undo, Save, etc.)
  • Alt-based navigation shortcuts
  • Function keys and system keys
  • Windows key combinations

Common Shortcut Patterns That Don’t Work

Alphanumeric-Only Shortcuts

The following are not supported:

  • A + B + C
  • 1 + 2 + 3
  • F + G

Too Many Keys

Shortcuts are limited to three keys:

  • Cmd + Shift + Option + K ❌
  • Ctrl + Shift + A + B ❌

Mixed Left and Right Modifiers

Using both sides of the same modifier is not supported:

  • Left Ctrl + Right Ctrl ❌
  • Left Alt + Right Alt ❌

Examples of Valid Shortcuts

These combinations generally work well:

  • Ctrl + Shift + K
  • Alt + F7
  • Cmd + Shift + 9
  • Ctrl + Space
  • Ctrl + Alt + M
  • Shift + F9

Final Tip

If a shortcut doesn’t work, try switching to a different modifier, using the right-hand side of the keyboard, or choosing a less commonly used key. This greatly reduces the chance of conflicts.