diff --git a/keyboards/kj_modify/rs40/info.json b/keyboards/kj_modify/rs40/info.json
new file mode 100644
index 0000000000..dfedf672c3
--- /dev/null
+++ b/keyboards/kj_modify/rs40/info.json
@@ -0,0 +1,77 @@
+{
+    "manufacturer": "KJ-Modify",
+    "keyboard_name": "RS40",
+    "maintainer": "Audite Marlow",
+    "bootloader": "stm32-dfu",
+    "diode_direction": "ROW2COL",
+    "features": {
+        "bootmagic": true,
+        "command": false,
+        "console": false,
+        "extrakey": true,
+        "mousekey": true,
+        "nkro": true
+    },
+    "matrix_pins": {
+        "cols": ["B12", "B14", "B15", "A8", "A9", "C13", "B9", "B8", "B5", "B4", "B3", "A15"],
+        "rows": ["B13", "A10", "B1", "B10"]
+    },
+    "processor": "STM32F401",
+    "url": "https://www.aliexpress.com/store/911983021",
+    "usb": {
+        "device_version": "1.0.0",
+        "pid": "0x5253",
+        "vid": "0x4B4A"
+    },
+    "layouts": {
+        "LAYOUT": {
+            "layout": [
+                {"x": 0,     "y": 0, "w": 1,    "matrix": [0, 0],  "label": "ESC"},
+                {"x": 1,     "y": 0, "w": 1,    "matrix": [0, 1],  "label": "Q"},
+                {"x": 2,     "y": 0, "w": 1,    "matrix": [0, 2],  "label": "W"},
+                {"x": 3,     "y": 0, "w": 1,    "matrix": [0, 3],  "label": "E"},
+                {"x": 4,     "y": 0, "w": 1,    "matrix": [0, 4],  "label": "R"},
+                {"x": 5,     "y": 0, "w": 1,    "matrix": [0, 5],  "label": "T"},
+                {"x": 6,     "y": 0, "w": 1,    "matrix": [0, 6],  "label": "Y"},
+                {"x": 7,     "y": 0, "w": 1,    "matrix": [0, 7],  "label": "U"},
+                {"x": 8,     "y": 0, "w": 1,    "matrix": [0, 8],  "label": "I"},
+                {"x": 9,     "y": 0, "w": 1,    "matrix": [0, 9],  "label": "O"},
+                {"x": 10,    "y": 0, "w": 1,    "matrix": [0, 10], "label": "P"},
+                {"x": 11,    "y": 0, "w": 1,    "matrix": [0, 11], "label": "BACKSPACE"},
+
+                {"x": 0,     "y": 1, "w": 1.25, "matrix": [1, 0],  "label": "CAPSLOCK"},
+                {"x": 1.25,  "y": 1, "w": 1,    "matrix": [1, 1],  "label": "A"},
+                {"x": 2.25,  "y": 1, "w": 1,    "matrix": [1, 2],  "label": "S"},
+                {"x": 3.25,  "y": 1, "w": 1,    "matrix": [1, 3],  "label": "D"},
+                {"x": 4.25,  "y": 1, "w": 1,    "matrix": [1, 4],  "label": "F"},
+                {"x": 5.25,  "y": 1, "w": 1,    "matrix": [1, 5],  "label": "G"},
+                {"x": 6.25,  "y": 1, "w": 1,    "matrix": [1, 6],  "label": "H"},
+                {"x": 7.25,  "y": 1, "w": 1,    "matrix": [1, 7],  "label": "J"},
+                {"x": 8.25,  "y": 1, "w": 1,    "matrix": [1, 8],  "label": "K"},
+                {"x": 9.25,  "y": 1, "w": 1,    "matrix": [1, 9],  "label": "L"},
+                {"x": 10.25, "y": 1, "w": 1.75, "matrix": [1, 11], "label": "ENTER"},
+
+                {"x": 0,     "y": 2, "w": 1.75, "matrix": [2, 0],  "label": "LSHIFT"},
+                {"x": 1.75,  "y": 2, "w": 1,    "matrix": [2, 2],  "label": "Z"},
+                {"x": 2.75,  "y": 2, "w": 1,    "matrix": [2, 3],  "label": "X"},
+                {"x": 3.75,  "y": 2, "w": 1,    "matrix": [2, 4],  "label": "C"},
+                {"x": 4.75,  "y": 2, "w": 1,    "matrix": [2, 5],  "label": "V"},
+                {"x": 5.75,  "y": 2, "w": 1,    "matrix": [2, 6],  "label": "B"},
+                {"x": 6.75,  "y": 2, "w": 1,    "matrix": [2, 7],  "label": "N"},
+                {"x": 7.75,  "y": 2, "w": 1,    "matrix": [2, 8],  "label": "M"},
+                {"x": 8.75,  "y": 2, "w": 1,    "matrix": [2, 9],  "label": "COMMA"},
+                {"x": 9.75,  "y": 2, "w": 1,    "matrix": [2, 10], "label": "PERIOD"},
+                {"x": 10.75, "y": 2, "w": 1.25, "matrix": [2, 11], "label": "RSHIFT"},
+
+                {"x": 1,     "y": 3, "w": 1.25, "matrix": [3, 0],  "label": "LCTRL"},
+                {"x": 1.25,  "y": 3, "w": 1,    "matrix": [3, 1],  "label": "FN2"},
+                {"x": 2.25,  "y": 3, "w": 1.25, "matrix": [3, 2],  "label": "WIN"},
+                {"x": 3.5,   "y": 3, "w": 2.25, "matrix": [3, 4],  "label": "SPACE"},
+                {"x": 5.75,  "y": 3, "w": 2.75, "matrix": [3, 7],  "label": "FN"},
+                {"x": 8.5,   "y": 3, "w": 1.25, "matrix": [3, 9],  "label": "SLASH"},
+                {"x": 9.75,  "y": 3, "w": 1,    "matrix": [3, 10], "label": "SEMICOLON"},
+                {"x": 10.75, "y": 3, "w": 1.25, "matrix": [3, 11], "label": "RCTRL"}
+            ]
+        }
+    }
+}
diff --git a/keyboards/kj_modify/rs40/keymaps/default/keymap.c b/keyboards/kj_modify/rs40/keymaps/default/keymap.c
new file mode 100644
index 0000000000..03cda315c8
--- /dev/null
+++ b/keyboards/kj_modify/rs40/keymaps/default/keymap.c
@@ -0,0 +1,25 @@
+// Copyright 2023 Audite Marlow (@auditemarlow)
+// SPDX-License-Identifier: GPL-3.0
+
+#include QMK_KEYBOARD_H
+
+const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
+    [0] = LAYOUT(
+        KC_ESC,  KC_Q,    KC_W,    KC_E,    KC_R,    KC_T,    KC_Y,    KC_U,    KC_I,    KC_O,    KC_P,    KC_BSPC,
+        KC_CAPS, KC_A,    KC_S,    KC_D,    KC_F,    KC_G,    KC_H,    KC_J,    KC_K,    KC_L,             KC_ENT,
+        KC_LSFT,          KC_Z,    KC_X,    KC_C,    KC_V,    KC_B,    KC_N,    KC_M,    KC_COMM, KC_DOT,  KC_RSFT,
+        KC_LCTL, MO(2),   KC_LGUI,          KC_SPC,                    MO(1),            KC_SLSH, KC_SCLN, KC_QUES
+    ),
+	[1] = LAYOUT(
+		_______, KC_1,    KC_2,    KC_3,    KC_4,    KC_5,    KC_6,    KC_7,    KC_8,    KC_9,    KC_0,    _______,
+		KC_TAB,  KC_BSLS, KC_QUOT, KC_GRV,  KC_LABK, KC_RABK, KC_MINS, KC_EQL,  KC_LBRC, KC_RBRC,          KC_DEL,
+		_______,          _______, _______, _______, _______, _______, _______, _______, _______, _______, _______,
+		_______, KC_LGUI, KC_LALT,          _______,                   _______,          _______, _______, _______
+	),
+	[2] = LAYOUT(
+		KC_F1,   KC_F2,   KC_F3,   KC_F4,   KC_F5,   KC_F6,   KC_F7,   KC_F8,   KC_F9,   KC_F10,  KC_F11,  KC_F12,
+		_______, _______, _______, _______, _______, _______, _______, _______, _______, _______,          _______,
+		_______,          _______, _______, _______, _______, _______, _______, _______, _______, KC_UP,   _______,
+		_______, _______, _______,          _______,                   _______,          KC_LEFT, KC_DOWN, KC_RIGHT
+	)
+};
diff --git a/keyboards/kj_modify/rs40/readme.md b/keyboards/kj_modify/rs40/readme.md
new file mode 100644
index 0000000000..a5bcce2796
--- /dev/null
+++ b/keyboards/kj_modify/rs40/readme.md
@@ -0,0 +1,25 @@
+# RS40
+
+A compact 40% keyboard with 42 keys.
+
+* Keyboard Maintainer: [Audite Marlow](https://github.com/auditemarlow)
+* Hardware Supported: RS40 PCB
+* Hardware Availability: https://www.aliexpress.com/store/911983021
+
+Make example for this keyboard (after setting up your build environment):
+
+    make kj_modify/rs40:default
+
+Flashing example for this keyboard:
+
+    make kj_modify/rs40:default:flash
+
+See the [build environment setup](https://docs.qmk.fm/#/getting_started_build_tools) and the [make instructions](https://docs.qmk.fm/#/getting_started_make_guide) for more information. Brand new to QMK? Start with our [Complete Newbs Guide](https://docs.qmk.fm/#/newbs).
+
+## Bootloader
+
+Enter the bootloader in 3 ways:
+
+* **Bootmagic reset**: Hold down the key at (0,0) in the matrix (usually the top left key or Escape) and plug in the keyboard
+* **Physical reset button**: Briefly press the button on the back of the PCB - some may have pads you must short instead
+* **Keycode in layout**: Press the key mapped to `QK_BOOT` if it is available
diff --git a/keyboards/kj_modify/rs40/rules.mk b/keyboards/kj_modify/rs40/rules.mk
new file mode 100644
index 0000000000..6e7633bfe0
--- /dev/null
+++ b/keyboards/kj_modify/rs40/rules.mk
@@ -0,0 +1 @@
+# This file intentionally left blank