# Left vs right modifier keys, eg. L-shift vs r-shift

**URL:** <https://forum.bome.com/t/left-vs-right-modifier-keys-eg-l-shift-vs-r-shift/7541>\
**Category:** Bome Products\
**Tags:** midi-translator, mac\
**Created:** [August 27, 2025, 4:58pm UTC](https://forum.bome.com/t/left-vs-right-modifier-keys-eg-l-shift-vs-r-shift/7541 "2025-08-27T16:58:55Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![ilovesoca](https://forum.bome.com/user_avatar/forum.bome.com/ilovesoca/32/6195_2.png) [@ilovesoca](https://forum.bome.com/u/ilovesoca)\
**Post date:** [August 27, 2025, 4:58pm UTC](https://forum.bome.com/t/left-vs-right-modifier-keys-eg-l-shift-vs-r-shift/7541/1 "2025-08-27T16:58:55Z")

</div>

Is there a way MTPro can recognize the difference between left and right modifier keys, such as L\_Shift and R\_Shift, on Mac OS?

Currently, under Incoming / Shortcut, there are no such options that I have been able to find. I’ve checked automatic recognition, the checkboxes, and the ‘Special Key …’ dropdown menu.

Thanks!

---

<div class="post-metadata">

**Author:** ![SteveC](https://forum.bome.com/user_avatar/forum.bome.com/stevec/32/8250_2.png) [@SteveC](https://forum.bome.com/u/SteveC)\
**Post date:** [August 27, 2025, 7:33pm UTC](https://forum.bome.com/t/left-vs-right-modifier-keys-eg-l-shift-vs-r-shift/7541/3 "2025-08-27T19:33:12Z")

</div>

I don’t there there is a differentiator between left and right shift on a Mac.

Steve Caldwell  
Bome Customer Care

* * *
_Also available for paid consulting services: bome@sniz.biz_

---

<div class="post-metadata">

**Author:** ![ilovesoca](https://forum.bome.com/user_avatar/forum.bome.com/ilovesoca/32/6195_2.png) [@ilovesoca](https://forum.bome.com/u/ilovesoca)\
**Post date:** [November 9, 2025, 10:10pm UTC](https://forum.bome.com/t/left-vs-right-modifier-keys-eg-l-shift-vs-r-shift/7541/4 "2025-11-09T22:10:58Z")

</div>

Ah, okay, I looked into it and I guess this is a pie-in-the-sky feature request, Here are the details (from the AI):

### **1. What macOS receives**

- At the **HID level** (what QMK sends), the left and right versions of Control, Shift, Option (Alt), and Command are **different usages**.
- macOS’s event system **does preserve** that distinction in the low-level APIs:
  - CoreGraphics CGEventFlags has separate bits for **LeftCommand/RightCommand** , **LeftShift/RightShift** , etc.
  - IOHID and HIDEventSystem APIs can also tell left vs right explicitly.

- So if you write a driver, or use a low-level listener like Karabiner-Elements, you can detect **left vs right modifiers independently**.

### **2. What typical macOS apps see**

- **NSEvent.ModifierFlags** (the high-level AppKit API) **collapses** left+right into a single flag per modifier. For example: pressing either Shift key just sets .shift. There’s no way in AppKit alone to ask “was it left or right shift?”.

---

<div class="post-metadata">

**Author:** ![FlorianBome](https://forum.bome.com/user_avatar/forum.bome.com/florianbome/32/2367_2.png) [@FlorianBome](https://forum.bome.com/u/FlorianBome)\
**Post date:** [November 10, 2025, 10:32am UTC](https://forum.bome.com/t/left-vs-right-modifier-keys-eg-l-shift-vs-r-shift/7541/6 "2025-11-10T10:32:38Z")

</div>

In general, we would like to support a distinction of left vs. right SHIFT (and the other modifiers).

However, first of all, there is the problem that there are only 2 SHIFT keys, but we would like to support 3 different SHIFT variants:

1. SHIFT: triggers on both left and right
2. LEFT SHIFT: left shift only
3. RIGHT SHIFT: right shift only

We don’t know how you could type keys to allow all 3 variants. Using the drop-down would not allow you to use that SHIFT variant as modifier (i.e. for keystroke combinations).

Current state is that on Windows, using the right SHIFT key will result in a right-only RIGHT SHIFT, but there is not way to enter LEFT SHIFT. On Mac, as you’ve noticed, we have not implemented a distinction of left vs. right at all.

What would be your use case?