diff --git a/Marlin/src/core/utility.h b/Marlin/src/core/utility.h
index d248091ce5..91c9533ab0 100644
--- a/Marlin/src/core/utility.h
+++ b/Marlin/src/core/utility.h
@@ -78,6 +78,7 @@ public:
 constexpr uint8_t ui8_to_percent(const uint8_t i) { return (int(i) * 100 + 127) / 255; }
 
 const xyze_char_t axis_codes LOGICAL_AXIS_ARRAY('E', 'X', 'Y', 'Z', AXIS4_NAME, AXIS5_NAME, AXIS6_NAME);
+const xyze_char_t iaxis_codes LOGICAL_AXIS_ARRAY('E', 'X', 'Y', 'Z', 'I', 'J', 'K');
 
 #if LINEAR_AXES <= XYZ
   #define AXIS_CHAR(A) ((char)('X' + A))
diff --git a/Marlin/src/gcode/calibrate/M666.cpp b/Marlin/src/gcode/calibrate/M666.cpp
index aa8ba26bb6..37d8a8facf 100644
--- a/Marlin/src/gcode/calibrate/M666.cpp
+++ b/Marlin/src/gcode/calibrate/M666.cpp
@@ -45,7 +45,7 @@
     DEBUG_SECTION(log_M666, "M666", DEBUGGING(LEVELING));
     bool is_err = false, is_set = false;
     LOOP_LINEAR_AXES(i) {
-      if (parser.seen(AXIS_CHAR(i))) {
+      if (parser.seenval(AXIS_CHAR(i))) {
         is_set = true;
         const float v = parser.value_linear_units();
         if (v > 0)
diff --git a/Marlin/src/gcode/config/M281.cpp b/Marlin/src/gcode/config/M281.cpp
index b90de6be30..e4ef3ab40b 100644
--- a/Marlin/src/gcode/config/M281.cpp
+++ b/Marlin/src/gcode/config/M281.cpp
@@ -47,8 +47,8 @@ void GcodeSuite::M281() {
         return;
       }
     #endif
-    if (parser.seen('L')) servo_angles[servo_index][0] = parser.value_int();
-    if (parser.seen('U')) servo_angles[servo_index][1] = parser.value_int();
+    if (parser.seenval('L')) servo_angles[servo_index][0] = parser.value_int();
+    if (parser.seenval('U')) servo_angles[servo_index][1] = parser.value_int();
   }
   else
     SERIAL_ERROR_MSG("Servo ", servo_index, " out of range");
diff --git a/Marlin/src/gcode/config/M304.cpp b/Marlin/src/gcode/config/M304.cpp
index 97dc4be25e..c970288238 100644
--- a/Marlin/src/gcode/config/M304.cpp
+++ b/Marlin/src/gcode/config/M304.cpp
@@ -36,9 +36,9 @@
  */
 void GcodeSuite::M304() {
   if (!parser.seen("PID")) return M304_report();
-  if (parser.seen('P')) thermalManager.temp_bed.pid.Kp = parser.value_float();
-  if (parser.seen('I')) thermalManager.temp_bed.pid.Ki = scalePID_i(parser.value_float());
-  if (parser.seen('D')) thermalManager.temp_bed.pid.Kd = scalePID_d(parser.value_float());
+  if (parser.seenval('P')) thermalManager.temp_bed.pid.Kp = parser.value_float();
+  if (parser.seenval('I')) thermalManager.temp_bed.pid.Ki = scalePID_i(parser.value_float());
+  if (parser.seenval('D')) thermalManager.temp_bed.pid.Kd = scalePID_d(parser.value_float());
 }
 
 void GcodeSuite::M304_report(const bool forReplay/*=true*/) {
diff --git a/Marlin/src/gcode/config/M305.cpp b/Marlin/src/gcode/config/M305.cpp
index 6957eef050..e7746923b3 100644
--- a/Marlin/src/gcode/config/M305.cpp
+++ b/Marlin/src/gcode/config/M305.cpp
@@ -52,19 +52,19 @@ void GcodeSuite::M305() {
   if (t_index >= (USER_THERMISTORS) || (do_set && t_index < 0))
     SERIAL_ECHO_MSG("!Invalid index. (0 <= P <= ", USER_THERMISTORS - 1, ")");
   else if (do_set) {
-    if (parser.seen('R')) // Pullup resistor value
+    if (parser.seenval('R')) // Pullup resistor value
       if (!thermalManager.set_pull_up_res(t_index, parser.value_float()))
         SERIAL_ECHO_MSG("!Invalid series resistance. (0 < R < 1000000)");
 
-    if (parser.seen('T')) // Resistance at 25C
+    if (parser.seenval('T')) // Resistance at 25C
       if (!thermalManager.set_res25(t_index, parser.value_float()))
         SERIAL_ECHO_MSG("!Invalid 25C resistance. (0 < T < 10000000)");
 
-    if (parser.seen('B')) // Beta value
+    if (parser.seenval('B')) // Beta value
       if (!thermalManager.set_beta(t_index, parser.value_float()))
         SERIAL_ECHO_MSG("!Invalid beta. (0 < B < 1000000)");
 
-    if (parser.seen('C')) // Steinhart-Hart C coefficient
+    if (parser.seenval('C')) // Steinhart-Hart C coefficient
       if (!thermalManager.set_sh_coeff(t_index, parser.value_float()))
         SERIAL_ECHO_MSG("!Invalid Steinhart-Hart C coeff. (-0.01 < C < +0.01)");
   }                       // If not setting then report parameters
diff --git a/Marlin/src/gcode/control/M17_M18_M84.cpp b/Marlin/src/gcode/control/M17_M18_M84.cpp
index ac3a602687..7630dcff46 100644
--- a/Marlin/src/gcode/control/M17_M18_M84.cpp
+++ b/Marlin/src/gcode/control/M17_M18_M84.cpp
@@ -125,14 +125,8 @@ void GcodeSuite::M17() {
             stepper.enable_e_steppers();
         }
       #endif
-      LINEAR_AXIS_CODE(
-        if (parser.seen_test('X'))        stepper.enable_axis(X_AXIS),
-        if (parser.seen_test('Y'))        stepper.enable_axis(Y_AXIS),
-        if (parser.seen_test('Z'))        stepper.enable_axis(Z_AXIS),
-        if (parser.seen_test(AXIS4_NAME)) stepper.enable_axis(I_AXIS),
-        if (parser.seen_test(AXIS5_NAME)) stepper.enable_axis(J_AXIS),
-        if (parser.seen_test(AXIS6_NAME)) stepper.enable_axis(K_AXIS)
-      );
+      LOOP_LINEAR_AXES(a)
+        if (parser.seen_test(AXIS_CHAR(a))) stepper.enable_axis((AxisEnum)a);
     }
   }
   else {
@@ -238,14 +232,8 @@ void GcodeSuite::M18_M84() {
               stepper.disable_e_steppers();
           }
         #endif
-        LINEAR_AXIS_CODE(
-          if (parser.seen_test('X'))        stepper.disable_axis(X_AXIS),
-          if (parser.seen_test('Y'))        stepper.disable_axis(Y_AXIS),
-          if (parser.seen_test('Z'))        stepper.disable_axis(Z_AXIS),
-          if (parser.seen_test(AXIS4_NAME)) stepper.disable_axis(I_AXIS),
-          if (parser.seen_test(AXIS5_NAME)) stepper.disable_axis(J_AXIS),
-          if (parser.seen_test(AXIS6_NAME)) stepper.disable_axis(K_AXIS)
-        );
+        LOOP_LINEAR_AXES(a)
+          if (parser.seen_test(AXIS_CHAR(a))) stepper.disable_axis((AxisEnum)a);
       }
     }
     else
diff --git a/Marlin/src/gcode/control/M280.cpp b/Marlin/src/gcode/control/M280.cpp
index 930542999e..82981e44bc 100644
--- a/Marlin/src/gcode/control/M280.cpp
+++ b/Marlin/src/gcode/control/M280.cpp
@@ -48,7 +48,7 @@ void GcodeSuite::M280() {
       const int anew = parser.value_int();
       if (anew >= 0) {
         #if ENABLED(POLARGRAPH)
-          if (parser.seen('T')) { // (ms) Total duration of servo move
+          if (parser.seenval('T')) { // (ms) Total duration of servo move
             const int16_t t = constrain(parser.value_int(), 0, 10000);
             const int aold = servo[servo_index].read();
             millis_t now = millis();
diff --git a/Marlin/src/gcode/control/M3-M5.cpp b/Marlin/src/gcode/control/M3-M5.cpp
index a619b1b762..817ed4fcb4 100644
--- a/Marlin/src/gcode/control/M3-M5.cpp
+++ b/Marlin/src/gcode/control/M3-M5.cpp
@@ -93,7 +93,7 @@ void GcodeSuite::M3_M4(const bool is_M4) {
       // Laser power in inline mode
       cutter.inline_direction(is_M4); // Should always be unused
       #if ENABLED(SPINDLE_LASER_USE_PWM)
-        if (parser.seen('O')) {
+        if (parser.seenval('O')) {
           cutter.unitPower = cutter.power_to_range(parser.value_byte(), 0);
           cutter.inline_ocr_power(cutter.unitPower); // The OCR is a value from 0 to 255 (uint8_t)
         }
diff --git a/Marlin/src/gcode/control/M350_M351.cpp b/Marlin/src/gcode/control/M350_M351.cpp
index a92238e4bb..d0ab75bb00 100644
--- a/Marlin/src/gcode/control/M350_M351.cpp
+++ b/Marlin/src/gcode/control/M350_M351.cpp
@@ -33,9 +33,9 @@
  * Warning: Steps-per-unit remains unchanged.
  */
 void GcodeSuite::M350() {
-  if (parser.seen('S')) LOOP_LE_N(i, 4) stepper.microstep_mode(i, parser.value_byte());
-  LOOP_LOGICAL_AXES(i) if (parser.seen(axis_codes[i])) stepper.microstep_mode(i, parser.value_byte());
-  if (parser.seen('B')) stepper.microstep_mode(4, parser.value_byte());
+  if (parser.seen('S')) LOOP_DISTINCT_AXES(i) stepper.microstep_mode(i, parser.value_byte());
+  LOOP_LOGICAL_AXES(i) if (parser.seenval(AXIS_CHAR(i))) stepper.microstep_mode(i, parser.value_byte());
+  if (parser.seenval('B')) stepper.microstep_mode(E_AXIS + 1, parser.value_byte());
   stepper.microstep_readings();
 }
 
diff --git a/Marlin/src/gcode/control/M605.cpp b/Marlin/src/gcode/control/M605.cpp
index 788659e7e2..c327b977ee 100644
--- a/Marlin/src/gcode/control/M605.cpp
+++ b/Marlin/src/gcode/control/M605.cpp
@@ -64,7 +64,7 @@
   void GcodeSuite::M605() {
     planner.synchronize();
 
-    if (parser.seen('S')) {
+    if (parser.seenval('S')) {
       const DualXMode previous_mode = dual_x_carriage_mode;
 
       dual_x_carriage_mode = (DualXMode)parser.value_byte();
@@ -78,8 +78,8 @@
 
         case DXC_DUPLICATION_MODE:
           // Set the X offset, but no less than the safety gap
-          if (parser.seen('X')) duplicate_extruder_x_offset = _MAX(parser.value_linear_units(), (X2_MIN_POS) - (X1_MIN_POS));
-          if (parser.seen('R')) duplicate_extruder_temp_offset = parser.value_celsius_diff();
+          if (parser.seenval('X')) duplicate_extruder_x_offset = _MAX(parser.value_linear_units(), (X2_MIN_POS) - (X1_MIN_POS));
+          if (parser.seenval('R')) duplicate_extruder_temp_offset = parser.value_celsius_diff();
           // Always switch back to tool 0
           if (active_extruder != 0) tool_change(0);
           break;
diff --git a/Marlin/src/gcode/feature/cancel/M486.cpp b/Marlin/src/gcode/feature/cancel/M486.cpp
index 1f14ae0fd2..c1e90d1b96 100644
--- a/Marlin/src/gcode/feature/cancel/M486.cpp
+++ b/Marlin/src/gcode/feature/cancel/M486.cpp
@@ -44,14 +44,14 @@ void GcodeSuite::M486() {
     cancelable.object_count = parser.intval('T', 1);
   }
 
-  if (parser.seen('S'))
+  if (parser.seenval('S'))
     cancelable.set_active_object(parser.value_int());
 
   if (parser.seen('C')) cancelable.cancel_active_object();
 
-  if (parser.seen('P')) cancelable.cancel_object(parser.value_int());
+  if (parser.seenval('P')) cancelable.cancel_object(parser.value_int());
 
-  if (parser.seen('U')) cancelable.uncancel_object(parser.value_int());
+  if (parser.seenval('U')) cancelable.uncancel_object(parser.value_int());
 }
 
 #endif // CANCEL_OBJECTS
diff --git a/Marlin/src/gcode/feature/i2c/M260_M261.cpp b/Marlin/src/gcode/feature/i2c/M260_M261.cpp
index e978fb5048..cf9bb7e583 100644
--- a/Marlin/src/gcode/feature/i2c/M260_M261.cpp
+++ b/Marlin/src/gcode/feature/i2c/M260_M261.cpp
@@ -45,10 +45,10 @@
  */
 void GcodeSuite::M260() {
   // Set the target address
-  if (parser.seen('A')) i2c.address(parser.value_byte());
+  if (parser.seenval('A')) i2c.address(parser.value_byte());
 
   // Add a new byte to the buffer
-  if (parser.seen('B')) i2c.addbyte(parser.value_byte());
+  if (parser.seenval('B')) i2c.addbyte(parser.value_byte());
 
   // Flush the buffer to the bus
   if (parser.seen('S')) i2c.send();
@@ -63,7 +63,7 @@ void GcodeSuite::M260() {
  * Usage: M261 A<slave device address base 10> B<number of bytes> S<style>
  */
 void GcodeSuite::M261() {
-  if (parser.seen('A')) i2c.address(parser.value_byte());
+  if (parser.seenval('A')) i2c.address(parser.value_byte());
 
   const uint8_t bytes = parser.byteval('B', 1),   // Bytes to request
                 style = parser.byteval('S');      // Serial output style (ASCII, HEX etc)
diff --git a/Marlin/src/gcode/feature/pause/G61.cpp b/Marlin/src/gcode/feature/pause/G61.cpp
index e0e1983a25..5e3c089135 100644
--- a/Marlin/src/gcode/feature/pause/G61.cpp
+++ b/Marlin/src/gcode/feature/pause/G61.cpp
@@ -71,7 +71,7 @@ void GcodeSuite::G61() {
     if (parser.seen(LINEAR_AXIS_GANG("X", "Y", "Z", STR_I, STR_J, STR_K))) {
       DEBUG_ECHOPGM(STR_RESTORING_POS " S", slot);
       LOOP_LINEAR_AXES(i) {
-        destination[i] = parser.seen(AXIS_CHAR(i))
+        destination[i] = parser.seenval(AXIS_CHAR(i))
           ? stored_position[slot][i] + parser.value_axis_units((AxisEnum)i)
           : current_position[i];
         DEBUG_CHAR(' ', AXIS_CHAR(i));
diff --git a/Marlin/src/gcode/feature/pause/M603.cpp b/Marlin/src/gcode/feature/pause/M603.cpp
index 10d14012f8..0512a0d29b 100644
--- a/Marlin/src/gcode/feature/pause/M603.cpp
+++ b/Marlin/src/gcode/feature/pause/M603.cpp
@@ -48,7 +48,7 @@ void GcodeSuite::M603() {
   if (target_extruder < 0) return;
 
   // Unload length
-  if (parser.seen('U')) {
+  if (parser.seenval('U')) {
     fc_settings[target_extruder].unload_length = ABS(parser.value_axis_units(E_AXIS));
     #if ENABLED(PREVENT_LENGTHY_EXTRUDE)
       NOMORE(fc_settings[target_extruder].unload_length, EXTRUDE_MAXLENGTH);
@@ -56,7 +56,7 @@ void GcodeSuite::M603() {
   }
 
   // Load length
-  if (parser.seen('L')) {
+  if (parser.seenval('L')) {
     fc_settings[target_extruder].load_length = ABS(parser.value_axis_units(E_AXIS));
     #if ENABLED(PREVENT_LENGTHY_EXTRUDE)
       NOMORE(fc_settings[target_extruder].load_length, EXTRUDE_MAXLENGTH);
diff --git a/Marlin/src/gcode/feature/pause/M701_M702.cpp b/Marlin/src/gcode/feature/pause/M701_M702.cpp
index 135b3d384e..ccaab25531 100644
--- a/Marlin/src/gcode/feature/pause/M701_M702.cpp
+++ b/Marlin/src/gcode/feature/pause/M701_M702.cpp
@@ -106,8 +106,8 @@ void GcodeSuite::M701() {
   #else
     constexpr float     purge_length = ADVANCED_PAUSE_PURGE_LENGTH,
                     slow_load_length = FILAMENT_CHANGE_SLOW_LOAD_LENGTH;
-        const float fast_load_length = ABS(parser.seen('L') ? parser.value_axis_units(E_AXIS)
-                                                            : fc_settings[active_extruder].load_length);
+        const float fast_load_length = ABS(parser.seenval('L') ? parser.value_axis_units(E_AXIS)
+                                                               : fc_settings[active_extruder].load_length);
     load_filament(
       slow_load_length, fast_load_length, purge_length,
       FILAMENT_CHANGE_ALERT_BEEPS,
diff --git a/Marlin/src/gcode/feature/runout/M412.cpp b/Marlin/src/gcode/feature/runout/M412.cpp
index bcf1e9f1b1..4b4ab6a68a 100644
--- a/Marlin/src/gcode/feature/runout/M412.cpp
+++ b/Marlin/src/gcode/feature/runout/M412.cpp
@@ -48,7 +48,7 @@ void GcodeSuite::M412() {
     if (seenR || seenS) runout.reset();
     if (seenS) runout.enabled = parser.value_bool();
     #if HAS_FILAMENT_RUNOUT_DISTANCE
-      if (parser.seen('D')) runout.set_runout_distance(parser.value_linear_units());
+      if (parser.seenval('D')) runout.set_runout_distance(parser.value_linear_units());
     #endif
   }
   else {
diff --git a/Marlin/src/gcode/geometry/M206_M428.cpp b/Marlin/src/gcode/geometry/M206_M428.cpp
index b32d729969..726fc53ec1 100644
--- a/Marlin/src/gcode/geometry/M206_M428.cpp
+++ b/Marlin/src/gcode/geometry/M206_M428.cpp
@@ -40,13 +40,12 @@
 void GcodeSuite::M206() {
   if (!parser.seen_any()) return M206_report();
 
-  LOOP_LINEAR_AXES(i)
-    if (parser.seen(AXIS_CHAR(i)))
-      set_home_offset((AxisEnum)i, parser.value_linear_units());
+  LOOP_LINEAR_AXES(a)
+    if (parser.seenval(AXIS_CHAR(a))) set_home_offset((AxisEnum)a, parser.value_axis_units((AxisEnum)a));
 
   #if ENABLED(MORGAN_SCARA)
-    if (parser.seen('T')) set_home_offset(A_AXIS, parser.value_float()); // Theta
-    if (parser.seen('P')) set_home_offset(B_AXIS, parser.value_float()); // Psi
+    if (parser.seenval('T')) set_home_offset(A_AXIS, parser.value_float()); // Theta
+    if (parser.seenval('P')) set_home_offset(B_AXIS, parser.value_float()); // Psi
   #endif
 
   report_current_position();