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diff --git a/quantum/keycode_string.h b/quantum/keycode_string.h
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+// Copyright 2024-2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <stdint.h>
+
+#if KEYCODE_STRING_ENABLE
+
+/**
+ * @brief Formats a QMK keycode as a human-readable string.
+ *
+ * Given a keycode, like `KC_A`, this function returns a formatted string, like
+ * "KC_A". This is useful for debugging and diagnostics so that keys are more
+ * easily identified than they would be by raw numerical codes.
+ *
+ * @note The returned char* string should be used right away. The string memory
+ * is reused and will be overwritten by the next call to `keycode_string()`.
+ *
+ * Many common QMK keycodes are understood by this function, but not all.
+ * Recognized keycodes include:
+ *
+ *  - Most basic keycodes, including letters `KC_A` - `KC_Z`, digits `KC_0` -
+ *    `KC_9`, function keys `KC_F1` - `KC_F24`, and modifiers like `KC_LSFT`.
+ *
+ *  - Modified basic keycodes, like `S(KC_1)` (Shift + 1 = !).
+ *
+ *  - `MO`, `TO`, `TG`, `OSL`, `LM(layer,mod)`, `LT(layer,kc)` layer switches.
+ *
+ *  - One-shot mod `OSM(mod)` keycodes.
+ *
+ *  - Mod-tap `MT(mod, kc)` keycodes.
+ *
+ *  - Tap dance keycodes `TD(i)`.
+ *
+ *  - Swap hands keycodes `SH_T(kc)`, `SH_TOGG`, etc.
+ *
+ *  - Joystick keycodes `JS_n`.
+ *
+ *  - Programmable button keycodes `PB_n`.
+ *
+ *  - Unicode `UC(codepoint)` and Unicode Map `UM(i)` and `UP(i,j)` keycodes.
+ *
+ *  - Keyboard range keycodes `QK_KB_*`.
+ *
+ *  - User range (SAFE_RANGE) keycodes `QK_USER_*`.
+ *
+ * Keycodes involving mods like `OSM`, `LM`, `MT` are fully supported only where
+ * a single mod is applied.
+ *
+ * Unrecognized keycodes are printed numerically as hex values like `0x1ABC`.
+ *
+ * Optionally, use `keycode_string_names_user` or `keycode_string_names_kb` to
+ * define names for additional keycodes or override how any of the above are
+ * formatted.
+ *
+ * @param keycode  QMK keycode.
+ * @return         Stringified keycode.
+ */
+const char* get_keycode_string(uint16_t keycode);
+
+/** Defines a human-readable name for a keycode. */
+typedef struct {
+    uint16_t    keycode;
+    const char* name;
+} keycode_string_name_t;
+
+// clang-format off
+/**
+ * @brief Defines names for additional keycodes for `get_keycode_string()`.
+ *
+ * Define `KEYCODE_STRING_NAMES_USER` in your keymap.c to add names for
+ * additional keycodes to `keycode_string()`. This table may also be used to
+ * override how `keycode_string()` formats a keycode. For example, supposing
+ * keymap.c defines `MYMACRO1` and `MYMACRO2` as custom keycodes:
+ *
+ *     KEYCODE_STRING_NAMES_USER(
+ *         KEYCODE_STRING_NAME(MYMACRO1),
+ *         KEYCODE_STRING_NAME(MYMACRO2),
+ *         KEYCODE_STRING_NAME(KC_EXLM),
+ *     );
+ *
+ * The above defines names for `MYMACRO1` and `MYMACRO2`, and overrides
+ * `KC_EXLM` to format as "KC_EXLM" instead of the default "S(KC_1)".
+ */
+#    define KEYCODE_STRING_NAMES_USER(...)                                          \
+    static const keycode_string_name_t keycode_string_names_user[] = {__VA_ARGS__}; \
+    uint16_t keycode_string_names_size_user =                                       \
+        sizeof(keycode_string_names_user) / sizeof(keycode_string_name_t);          \
+    const keycode_string_name_t* keycode_string_names_data_user =                   \
+        keycode_string_names_user
+
+/** Same as above, but defines keycode string names at the keyboard level. */
+#    define KEYCODE_STRING_NAMES_KB(...)                                            \
+    static const keycode_string_name_t keycode_string_names_kb[] = {__VA_ARGS__};   \
+    uint16_t keycode_string_names_size_kb =                                         \
+        sizeof(keycode_string_names_kb) / sizeof(keycode_string_name_t);            \
+    const keycode_string_name_t* keycode_string_names_data_kb =                     \
+        keycode_string_names_kb
+
+/** Helper to define a keycode_string_name_t. */
+#    define KEYCODE_STRING_NAME(kc) \
+        { (kc), #kc }
+// clang-format on
+
+extern const keycode_string_name_t* keycode_string_names_data_user;
+extern uint16_t                     keycode_string_names_size_user;
+extern const keycode_string_name_t* keycode_string_names_data_kb;
+extern uint16_t                     keycode_string_names_size_kb;
+
+#else
+
+// When keycode_string is disabled, fall back to printing keycodes numerically
+// as decimal values, using get_u16_str() from quantum.c.
+#    define get_keycode_string(kc) get_u16_str(kc, ' ')
+
+const char* get_u16_str(uint16_t curr_num, char curr_pad);
+
+#    define KEYCODE_STRING_NAMES_USER(...)
+#    define KEYCODE_STRING_NAMES_KB(...)
+#    define KEYCODE_STRING_NAME(kc)
+
+#endif // KEYCODE_STRING_ENABLE