diff --git a/README.md b/README.md
index b08e101..2685e7a 100644
--- a/README.md
+++ b/README.md
@@ -24,8 +24,10 @@ ATM this needs to be cloned to
 
 to work properly.
 
-Based on ideas and code from:
+Based on
 
-- https://oxey.dev/dhorf
-- https://github.com/manna-harbour/miryoku
-- https://github.com/filterpaper/qmk_userspace
+https://oxey.dev/dhorf
+
+and
+
+https://github.com/manna-harbour/miryoku
diff --git a/common/achordion.c b/common/achordion.c
new file mode 100644
index 0000000..4968e9d
--- /dev/null
+++ b/common/achordion.c
@@ -0,0 +1,383 @@
+// Copyright 2022-2024 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.
+
+/**
+ * @file achordion.c
+ * @brief Achordion implementation
+ *
+ * For full documentation, see
+ * <https://getreuer.info/posts/keyboards/achordion>
+ */
+
+#include "achordion.h"
+
+#if !defined(IS_QK_MOD_TAP)
+// Attempt to detect out-of-date QMK installation, which would fail with
+// implicit-function-declaration errors in the code below.
+#error "achordion: QMK version is too old to build. Please update QMK."
+#else
+
+// Copy of the `record` and `keycode` args for the current active tap-hold key.
+static keyrecord_t tap_hold_record;
+static uint16_t tap_hold_keycode = KC_NO;
+// Timeout timer. When it expires, the key is considered held.
+static uint16_t hold_timer = 0;
+// Eagerly applied mods, if any.
+static uint8_t eager_mods = 0;
+// Flag to determine whether another key is pressed within the timeout.
+static bool pressed_another_key_before_release = false;
+
+#ifdef ACHORDION_STREAK
+// Timer for typing streak
+static uint16_t streak_timer = 0;
+#else
+// When disabled, is_streak is never true
+#define is_streak false
+#endif
+
+// Achordion's current state.
+enum {
+  // A tap-hold key is pressed, but hasn't yet been settled as tapped or held.
+  STATE_UNSETTLED,
+  // Achordion is inactive.
+  STATE_RELEASED,
+  // Active tap-hold key has been settled as tapped.
+  STATE_TAPPING,
+  // Active tap-hold key has been settled as held.
+  STATE_HOLDING,
+  // This state is set while calling `process_record()`, which will recursively
+  // call `process_achordion()`. This state is checked so that we don't process
+  // events generated by Achordion and potentially create an infinite loop.
+  STATE_RECURSING,
+};
+static uint8_t achordion_state = STATE_RELEASED;
+
+#ifdef ACHORDION_STREAK
+static void update_streak_timer(uint16_t keycode, keyrecord_t* record) {
+  if (achordion_streak_continue(keycode)) {
+    // We use 0 to represent an unset timer, so `| 1` to force a nonzero value.
+    streak_timer = record->event.time | 1;
+  } else {
+    streak_timer = 0;
+  }
+}
+#endif
+
+// Presses or releases eager_mods through process_action(), which skips the
+// usual event handling pipeline. The action is considered as a mod-tap hold or
+// release, with Retro Tapping if enabled.
+static void process_eager_mods_action(void) {
+  action_t action;
+  action.code = ACTION_MODS_TAP_KEY(
+      eager_mods, QK_MOD_TAP_GET_TAP_KEYCODE(tap_hold_keycode));
+  process_action(&tap_hold_record, action);
+}
+
+// Calls `process_record()` with state set to RECURSING.
+static void recursively_process_record(keyrecord_t* record, uint8_t state) {
+  achordion_state = STATE_RECURSING;
+#if defined(POINTING_DEVICE_ENABLE) && defined(POINTING_DEVICE_AUTO_MOUSE_ENABLE)
+  int8_t mouse_key_tracker = get_auto_mouse_key_tracker();
+#endif
+  process_record(record);
+#if defined(POINTING_DEVICE_ENABLE) && defined(POINTING_DEVICE_AUTO_MOUSE_ENABLE)
+  set_auto_mouse_key_tracker(mouse_key_tracker);
+#endif
+  achordion_state = state;
+}
+
+// Sends hold press event and settles the active tap-hold key as held.
+static void settle_as_hold(void) {
+  if (eager_mods) {
+    // If eager mods are being applied, nothing needs to be done besides
+    // updating the state.
+    dprintln("Achordion: Settled eager mod as hold.");
+    achordion_state = STATE_HOLDING;
+  } else {
+    // Create hold press event.
+    dprintln("Achordion: Plumbing hold press.");
+    recursively_process_record(&tap_hold_record, STATE_HOLDING);
+  }
+}
+
+// Sends tap press and release and settles the active tap-hold key as tapped.
+static void settle_as_tap(void) {
+  if (eager_mods) {  // Clear eager mods if set.
+#if defined(RETRO_TAPPING) || defined(RETRO_TAPPING_PER_KEY)
+#ifdef DUMMY_MOD_NEUTRALIZER_KEYCODE
+    neutralize_flashing_modifiers(get_mods());
+#endif  // DUMMY_MOD_NEUTRALIZER_KEYCODE
+#endif  // defined(RETRO_TAPPING) || defined(RETRO_TAPPING_PER_KEY)
+    tap_hold_record.event.pressed = false;
+    // To avoid falsely triggering Retro Tapping, process eager mods release as
+    // a regular mods release rather than a mod-tap release.
+    action_t action;
+    action.code = ACTION_MODS(eager_mods);
+    process_action(&tap_hold_record, action);
+    eager_mods = 0;
+  }
+
+  dprintln("Achordion: Plumbing tap press.");
+  tap_hold_record.event.pressed = true;
+  tap_hold_record.tap.count = 1;  // Revise event as a tap.
+  tap_hold_record.tap.interrupted = true;
+  // Plumb tap press event.
+  recursively_process_record(&tap_hold_record, STATE_TAPPING);
+
+  send_keyboard_report();
+#if TAP_CODE_DELAY > 0
+  wait_ms(TAP_CODE_DELAY);
+#endif  // TAP_CODE_DELAY > 0
+
+  dprintln("Achordion: Plumbing tap release.");
+  tap_hold_record.event.pressed = false;
+  // Plumb tap release event.
+  recursively_process_record(&tap_hold_record, STATE_TAPPING);
+}
+
+bool process_achordion(uint16_t keycode, keyrecord_t* record) {
+  // Don't process events that Achordion generated.
+  if (achordion_state == STATE_RECURSING) {
+    return true;
+  }
+
+  // Determine whether the current event is for a mod-tap or layer-tap key.
+  const bool is_mt = IS_QK_MOD_TAP(keycode);
+  const bool is_tap_hold = is_mt || IS_QK_LAYER_TAP(keycode);
+  // Check that this is a normal key event, don't act on combos.
+  const bool is_key_event = IS_KEYEVENT(record->event);
+
+  // Event while no tap-hold key is active.
+  if (achordion_state == STATE_RELEASED) {
+    if (is_tap_hold && record->tap.count == 0 && record->event.pressed &&
+        is_key_event) {
+      // A tap-hold key is pressed and considered by QMK as "held".
+      const uint16_t timeout = achordion_timeout(keycode);
+      if (timeout > 0) {
+        achordion_state = STATE_UNSETTLED;
+        // Save info about this key.
+        tap_hold_keycode = keycode;
+        tap_hold_record = *record;
+        hold_timer = record->event.time + timeout;
+        pressed_another_key_before_release = false;
+        eager_mods = 0;
+
+        if (is_mt) {  // Apply mods immediately if they are "eager."
+          const uint8_t mod = mod_config(QK_MOD_TAP_GET_MODS(keycode));
+          if (
+#if defined(CAPS_WORD_ENABLE) && defined(CAPS_WORD_INVERT_ON_SHIFT)
+              // Since eager mods bypass normal event handling, eager Shift does
+              // not work with CAPS_WORD_INVERT_ON_SHIFT. So if this option is
+              // enabled, we don't apply Shift eagerly when Caps Word is on.
+              !(is_caps_word_on() && (mod & MOD_LSFT) != 0) &&
+#endif  // defined(CAPS_WORD_ENABLE) && defined(CAPS_WORD_INVERT_ON_SHIFT)
+              achordion_eager_mod(mod)) {
+            eager_mods = mod;
+            process_eager_mods_action();
+          }
+        }
+
+        dprintf("Achordion: Key 0x%04X pressed.%s\n", keycode,
+                eager_mods ? " Set eager mods." : "");
+        return false;  // Skip default handling.
+      }
+    }
+
+#ifdef ACHORDION_STREAK
+    update_streak_timer(keycode, record);
+#endif
+    return true;  // Otherwise, continue with default handling.
+  } else if (record->event.pressed && tap_hold_keycode != keycode) {
+    // Track whether another key was pressed while using a tap-hold key.
+    pressed_another_key_before_release = true;
+  }
+
+  // Release of the active tap-hold key.
+  if (keycode == tap_hold_keycode && !record->event.pressed) {
+    if (eager_mods) {
+      dprintln("Achordion: Key released. Clearing eager mods.");
+      tap_hold_record.event.pressed = false;
+      process_eager_mods_action();
+    } else if (achordion_state == STATE_HOLDING) {
+      dprintln("Achordion: Key released. Plumbing hold release.");
+      tap_hold_record.event.pressed = false;
+      // Plumb hold release event.
+      recursively_process_record(&tap_hold_record, STATE_RELEASED);
+    } else if (!pressed_another_key_before_release) {
+      // No other key was pressed between the press and release of the tap-hold
+      // key, plumb a hold press and then a release.
+      dprintln("Achordion: Key released. Plumbing hold press and release.");
+      recursively_process_record(&tap_hold_record, STATE_HOLDING);
+      tap_hold_record.event.pressed = false;
+      recursively_process_record(&tap_hold_record, STATE_RELEASED);
+    } else {
+      dprintln("Achordion: Key released.");
+    }
+
+    achordion_state = STATE_RELEASED;
+    tap_hold_keycode = KC_NO;
+    return false;
+  }
+
+  if (achordion_state == STATE_UNSETTLED && record->event.pressed) {
+#ifdef ACHORDION_STREAK
+    const uint16_t s_timeout =
+        achordion_streak_chord_timeout(tap_hold_keycode, keycode);
+    const bool is_streak =
+        streak_timer && s_timeout &&
+        !timer_expired(record->event.time, (streak_timer + s_timeout));
+#endif
+
+    // Press event occurred on a key other than the active tap-hold key.
+
+    // If the other key is *also* a tap-hold key and considered by QMK to be
+    // held, then we settle the active key as held. This way, things like
+    // chording multiple home row modifiers will work, but let's our logic
+    // consider simply a single tap-hold key as "active" at a time.
+    //
+    // Otherwise, we call `achordion_chord()` to determine whether to settle the
+    // tap-hold key as tapped vs. held. We implement the tap or hold by plumbing
+    // events back into the handling pipeline so that QMK features and other
+    // user code can see them. This is done by calling `process_record()`, which
+    // in turn calls most handlers including `process_record_user()`.
+    if (!is_streak &&
+        (!is_key_event || (is_tap_hold && record->tap.count == 0) ||
+         achordion_chord(tap_hold_keycode, &tap_hold_record, keycode,
+                         record))) {
+      settle_as_hold();
+
+#ifdef REPEAT_KEY_ENABLE
+      // Edge case involving LT + Repeat Key: in a sequence of "LT down, other
+      // down" where "other" is on the other layer in the same position as
+      // Repeat or Alternate Repeat, the repeated keycode is set instead of the
+      // the one on the switched-to layer. Here we correct that.
+      if (get_repeat_key_count() != 0 && IS_QK_LAYER_TAP(tap_hold_keycode)) {
+        record->keycode = KC_NO;  // Forget the repeated keycode.
+        clear_weak_mods();
+      }
+#endif  // REPEAT_KEY_ENABLE
+    } else {
+      settle_as_tap();
+
+#ifdef ACHORDION_STREAK
+      update_streak_timer(keycode, record);
+      if (is_streak && is_key_event && is_tap_hold && record->tap.count == 0) {
+        // If we are in a streak and resolved the current tap-hold key as a tap
+        // consider the next tap-hold key as active to be resolved next.
+        update_streak_timer(tap_hold_keycode, &tap_hold_record);
+        const uint16_t timeout = achordion_timeout(keycode);
+        tap_hold_keycode = keycode;
+        tap_hold_record = *record;
+        hold_timer = record->event.time + timeout;
+        achordion_state = STATE_UNSETTLED;
+        pressed_another_key_before_release = false;
+        return false;
+      }
+#endif
+    }
+
+    recursively_process_record(record, achordion_state);  // Re-process event.
+    return false;  // Block the original event.
+  }
+
+#ifdef ACHORDION_STREAK
+  // update idle timer on regular keys event
+  update_streak_timer(keycode, record);
+#endif
+  return true;
+}
+
+void achordion_task(void) {
+  if (achordion_state == STATE_UNSETTLED &&
+      timer_expired(timer_read(), hold_timer)) {
+    settle_as_hold();  // Timeout expired, settle the key as held.
+  }
+
+#ifdef ACHORDION_STREAK
+#define MAX_STREAK_TIMEOUT 800
+  if (streak_timer &&
+      timer_expired(timer_read(), (streak_timer + MAX_STREAK_TIMEOUT))) {
+    streak_timer = 0;  // Expired.
+  }
+#endif
+}
+
+// Returns true if `pos` on the left hand of the keyboard, false if right.
+static bool on_left_hand(keypos_t pos) {
+#ifdef SPLIT_KEYBOARD
+  return pos.row < MATRIX_ROWS / 2;
+#else
+  return (MATRIX_COLS > MATRIX_ROWS) ? pos.col < MATRIX_COLS / 2
+                                     : pos.row < MATRIX_ROWS / 2;
+#endif
+}
+
+bool achordion_opposite_hands(const keyrecord_t* tap_hold_record,
+                              const keyrecord_t* other_record) {
+  return on_left_hand(tap_hold_record->event.key) !=
+         on_left_hand(other_record->event.key);
+}
+
+// By default, use the BILATERAL_COMBINATIONS rule to consider the tap-hold key
+// "held" only when it and the other key are on opposite hands.
+__attribute__((weak)) bool achordion_chord(uint16_t tap_hold_keycode,
+                                           keyrecord_t* tap_hold_record,
+                                           uint16_t other_keycode,
+                                           keyrecord_t* other_record) {
+  return achordion_opposite_hands(tap_hold_record, other_record);
+}
+
+// By default, the timeout is 1000 ms for all keys.
+__attribute__((weak)) uint16_t achordion_timeout(uint16_t tap_hold_keycode) {
+  return 1000;
+}
+
+// By default, Shift and Ctrl mods are eager, and Alt and GUI are not.
+__attribute__((weak)) bool achordion_eager_mod(uint8_t mod) {
+  return (mod & (MOD_LALT | MOD_LGUI)) == 0;
+}
+
+#ifdef ACHORDION_STREAK
+__attribute__((weak)) bool achordion_streak_continue(uint16_t keycode) {
+  // If any mods other than shift or AltGr are held, don't continue the streak
+  if (get_mods() & (MOD_MASK_CG | MOD_BIT_LALT)) return false;
+  // This function doesn't get called for holds, so convert to tap version of
+  // keycodes
+  if (IS_QK_MOD_TAP(keycode)) keycode = QK_MOD_TAP_GET_TAP_KEYCODE(keycode);
+  if (IS_QK_LAYER_TAP(keycode)) keycode = QK_LAYER_TAP_GET_TAP_KEYCODE(keycode);
+  // Regular letters and punctuation continue the streak.
+  if (keycode >= KC_A && keycode <= KC_Z) return true;
+  switch (keycode) {
+    case KC_DOT:
+    case KC_COMMA:
+    case KC_QUOTE:
+    case KC_SPACE:
+      return true;
+  }
+  // All other keys end the streak
+  return false;
+}
+
+__attribute__((weak)) uint16_t achordion_streak_chord_timeout(
+    uint16_t tap_hold_keycode, uint16_t next_keycode) {
+  return achordion_streak_timeout(tap_hold_keycode);
+}
+
+__attribute__((weak)) uint16_t
+achordion_streak_timeout(uint16_t tap_hold_keycode) {
+  return 200;
+}
+#endif
+
+#endif  // version check
diff --git a/common/achordion.h b/common/achordion.h
new file mode 100644
index 0000000..f1e08ec
--- /dev/null
+++ b/common/achordion.h
@@ -0,0 +1,193 @@
+// Copyright 2022-2024 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.
+
+/**
+ * @file achordion.h
+ * @brief Achordion: Customizing the tap-hold decision.
+ *
+ * Overview
+ * --------
+ *
+ * This library customizes when tap-hold keys are considered held vs. tapped
+ * based on the next pressed key, like Manna Harbour's Bilateral Combinations or
+ * ZMK's positional hold. The library works on top of QMK's existing tap-hold
+ * implementation. You define mod-tap and layer-tap keys as usual and use
+ * Achordion to fine-tune the behavior.
+ *
+ * When QMK settles a tap-hold key as held, Achordion intercepts the event.
+ * Achordion then revises the event as a tap or passes it along as a hold:
+ *
+ *  * Chord condition: On the next key press, a customizable `achordion_chord()`
+ *    function is called, which takes the tap-hold key and the next key pressed
+ *    as args. When the function returns true, the tap-hold key is settled as
+ *    held, and otherwise as tapped.
+ *
+ *  * Timeout: If no other key press occurs within a timeout, the tap-hold key
+ *    is settled as held. This is customizable with `achordion_timeout()`.
+ *
+ * Achordion only changes the behavior when QMK considered the key held. It
+ * changes some would-be holds to taps, but no taps to holds.
+ *
+ * @note Some QMK features handle events before the point where Achordion can
+ * intercept them, particularly: Combos, Key Lock, and Dynamic Macros. It's
+ * still possible to use these features and Achordion in your keymap, but beware
+ * they might behave poorly when used simultaneously with tap-hold keys.
+ *
+ *
+ * For full documentation, see
+ * <https://getreuer.info/posts/keyboards/achordion>
+ */
+
+#pragma once
+
+#include "quantum.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Handler function for Achordion.
+ *
+ * Call this function from `process_record_user()` as
+ *
+ *     #include "features/achordion.h"
+ *
+ *     bool process_record_user(uint16_t keycode, keyrecord_t* record) {
+ *       if (!process_achordion(keycode, record)) { return false; }
+ *       // Your macros...
+ *       return true;
+ *     }
+ */
+bool process_achordion(uint16_t keycode, keyrecord_t* record);
+
+/**
+ * Matrix task function for Achordion.
+ *
+ * Call this function from `matrix_scan_user()` as
+ *
+ *     void matrix_scan_user(void) {
+ *       achordion_task();
+ *     }
+ */
+void achordion_task(void);
+
+/**
+ * Optional callback to customize which key chords are considered "held".
+ *
+ * In your keymap.c, define the callback
+ *
+ *     bool achordion_chord(uint16_t tap_hold_keycode,
+ *                          keyrecord_t* tap_hold_record,
+ *                          uint16_t other_keycode,
+ *                          keyrecord_t* other_record) {
+ *        // Conditions...
+ *     }
+ *
+ * This callback is called if while `tap_hold_keycode` is pressed,
+ * `other_keycode` is pressed. Return true if the tap-hold key should be
+ * considered held, or false to consider it tapped.
+ *
+ * @param tap_hold_keycode Keycode of the tap-hold key.
+ * @param tap_hold_record keyrecord_t from the tap-hold press event.
+ * @param other_keycode Keycode of the other key.
+ * @param other_record keyrecord_t from the other key's press event.
+ * @return True if the tap-hold key should be considered held.
+ */
+bool achordion_chord(uint16_t tap_hold_keycode, keyrecord_t* tap_hold_record,
+                     uint16_t other_keycode, keyrecord_t* other_record);
+
+/**
+ * Optional callback to define a timeout duration per keycode.
+ *
+ * In your keymap.c, define the callback
+ *
+ *     uint16_t achordion_timeout(uint16_t tap_hold_keycode) {
+ *       // ...
+ *     }
+ *
+ * The callback determines Achordion's timeout duration for `tap_hold_keycode`
+ * in units of milliseconds. The timeout be in the range 0 to 32767 ms (upper
+ * bound is due to 16-bit timer limitations). Use a timeout of 0 to bypass
+ * Achordion.
+ *
+ * @param tap_hold_keycode Keycode of the tap-hold key.
+ * @return Timeout duration in milliseconds in the range 0 to 32767.
+ */
+uint16_t achordion_timeout(uint16_t tap_hold_keycode);
+
+/**
+ * Optional callback defining which mods are "eagerly" applied.
+ *
+ * This callback defines  which mods are "eagerly" applied while a mod-tap
+ * key is still being settled. This is helpful to reduce delay particularly when
+ * using mod-tap keys with an external mouse.
+ *
+ * Define this callback in your keymap.c. The default callback is eager for
+ * Shift and Ctrl, and not for Alt and GUI:
+ *
+ *     bool achordion_eager_mod(uint8_t mod) {
+ *       return (mod & (MOD_LALT | MOD_LGUI)) == 0;
+ *     }
+ *
+ * @note `mod` should be compared with `MOD_` prefixed codes, not `KC_` codes,
+ * described at <https://docs.qmk.fm/mod_tap>.
+ *
+ * @param mod Modifier `MOD_` code.
+ * @return True if the modifier should be eagerly applied.
+ */
+bool achordion_eager_mod(uint8_t mod);
+
+/**
+ * Returns true if the args come from keys on opposite hands.
+ *
+ * @param tap_hold_record keyrecord_t from the tap-hold key's event.
+ * @param other_record keyrecord_t from the other key's event.
+ * @return True if the keys are on opposite hands.
+ */
+bool achordion_opposite_hands(const keyrecord_t* tap_hold_record,
+                              const keyrecord_t* other_record);
+
+/**
+ * Suppress tap-hold mods within a *typing streak* by defining
+ * ACHORDION_STREAK. This can help preventing accidental mod
+ * activation when performing a fast tapping sequence.
+ * This is inspired by
+ * https://sunaku.github.io/home-row-mods.html#typing-streaks
+ *
+ * Enable with:
+ *
+ *    #define ACHORDION_STREAK
+ *
+ * Adjust the maximum time between key events before modifiers can be enabled
+ * by defining the following callback in your keymap.c:
+ *
+ *    uint16_t achordion_streak_chord_timeout(
+ *        uint16_t tap_hold_keycode, uint16_t next_keycode) {
+ *      return 200;  // Default of 200 ms.
+ *    }
+ */
+#ifdef ACHORDION_STREAK
+uint16_t achordion_streak_chord_timeout(uint16_t tap_hold_keycode,
+                                        uint16_t next_keycode);
+
+bool achordion_streak_continue(uint16_t keycode);
+
+/** @deprecated Use `achordion_streak_chord_timeout()` instead. */
+uint16_t achordion_streak_timeout(uint16_t tap_hold_keycode);
+#endif
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/common/config.h b/common/config.h
index 18ee2e7..53db981 100644
--- a/common/config.h
+++ b/common/config.h
@@ -1,5 +1,18 @@
-// Copyright Christoph Cullmann
-// SPDX-License-Identifier: GPL-2.0+
+/* Copyright 2022 Christoph Cullmann
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
 
 #pragma once
 
@@ -18,16 +31,21 @@
 // enable NKRO by default
 #define FORCE_NKRO
 
-// Tap-hold settings
-#define TAPPING_TERM 230
-#define TAPPING_TERM_PER_KEY
-#define PERMISSIVE_HOLD_PER_KEY
-#define HOLD_ON_OTHER_KEY_PRESS_PER_KEY
+// settings for home row modifiers
+// details see https://precondition.github.io/home-row-mods
 
-// Input intervals
-#define QUICK_TAP_TERM TAPPING_TERM - 100
-#define SHIFT_TAP_TERM TAPPING_TERM - 80
-#define COMBO_TAP_TERM TAPPING_TERM + 100
+// detect typing streaks
+#define ACHORDION_STREAK
+
+// Enable rapid switch from tap to hold, disables double tap hold auto-repeat.
+#define QUICK_TAP_TERM 0
+
+// home row mods
+#define TAPPING_FORCE_HOLD
+#define TAPPING_TERM 180
+
+// delay hold/release to not mess up software
+#define TAP_CODE_DELAY 10
 
 //
 // underglow configuration
diff --git a/common/keymap.h b/common/keymap.h
index 3fdba83..ef49bf5 100644
--- a/common/keymap.h
+++ b/common/keymap.h
@@ -1,5 +1,18 @@
-// Copyright Christoph Cullmann
-// SPDX-License-Identifier: GPL-2.0+
+/* Copyright 2022 Christoph Cullmann
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
 
 // our layers
 enum my_layers {
@@ -50,7 +63,25 @@ const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
 
 };
 
-#include "filterpaper.h"
+#include "achordion.h"
+
+bool process_record_user(uint16_t keycode, keyrecord_t* record) {
+  if (!process_achordion(keycode, record)) { return false; }
+  return true;
+}
+
+void matrix_scan_user(void) {
+  achordion_task();
+}
+
+bool achordion_chord(uint16_t tap_hold_keycode,
+                     keyrecord_t* tap_hold_record,
+                     uint16_t other_keycode,
+                     keyrecord_t* other_record) {
+  // follow the opposite hands rule.
+  return on_left_hand(tap_hold_record->event.key) !=
+         on_left_hand(other_record->event.key);
+}
 
 void keyboard_post_init_user(void) {
     // always use the same effect
diff --git a/common/rules.mk b/common/rules.mk
index 8881fa6..6854485 100644
--- a/common/rules.mk
+++ b/common/rules.mk
@@ -10,7 +10,8 @@ MOUSEKEY_ENABLE = no
 MUSIC_ENABLE = no
 SPACE_CADET_ENABLE = no
 
-REPEAT_KEY_ENABLE = yes
+# add achordion to improve home row modifiers
+SRC += /home/cullmann/data/qmk/christoph-cullmann/common/achordion.c
 
 # good optimizations
 LTO_ENABLE = yes
diff --git a/crkbd/config.h b/crkbd/config.h
index 96ffc1e..ac17ea4 100644
--- a/crkbd/config.h
+++ b/crkbd/config.h
@@ -1,5 +1,18 @@
-// Copyright Christoph Cullmann
-// SPDX-License-Identifier: GPL-2.0+
+/* Copyright 2022 Christoph Cullmann
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
 
 #pragma once
 
diff --git a/crkbd/keymap.c b/crkbd/keymap.c
index 3bbc212..52a1ec0 100644
--- a/crkbd/keymap.c
+++ b/crkbd/keymap.c
@@ -1,8 +1,27 @@
-// Copyright Christoph Cullmann
-// SPDX-License-Identifier: GPL-2.0+
+/* Copyright 2022 Christoph Cullmann
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
 
 #include QMK_KEYBOARD_H
 
+// Returns true if `pos` on the left hand of the keyboard, false if right.
+static bool on_left_hand(keypos_t pos)
+{
+    return pos.row < MATRIX_ROWS / 2;
+}
+
 // layout helper macro, we just use 42 keys
 #undef LAYOUT
 #define LAYOUT(\
diff --git a/planck/config.h b/planck/config.h
index f7ca78d..9093362 100644
--- a/planck/config.h
+++ b/planck/config.h
@@ -1,5 +1,18 @@
-// Copyright Christoph Cullmann
-// SPDX-License-Identifier: GPL-2.0+
+/* Copyright 2022 Christoph Cullmann
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
 
 #pragma once
 
diff --git a/planck/keymap.c b/planck/keymap.c
index 90243ac..2666e77 100644
--- a/planck/keymap.c
+++ b/planck/keymap.c
@@ -1,8 +1,27 @@
-// Copyright Christoph Cullmann
-// SPDX-License-Identifier: GPL-2.0+
+/* Copyright 2022 Christoph Cullmann
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
 
 #include QMK_KEYBOARD_H
 
+// Returns true if `pos` on the left hand of the keyboard, false if right.
+static bool on_left_hand(keypos_t pos)
+{
+    return (pos.row < 3) || (pos.row == 3 && pos.col < 3) || (pos.row == 7 && pos.col > 2);
+}
+
 // layout helper macro, we just use 42 keys
 #undef LAYOUT
 #define LAYOUT(\