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