diff --git a/src/py/bbctrl/AuxPreprocessor.py b/src/py/bbctrl/AuxPreprocessor.py
index 5a1ae48..10cd2ab 100644
--- a/src/py/bbctrl/AuxPreprocessor.py
+++ b/src/py/bbctrl/AuxPreprocessor.py
@@ -42,6 +42,30 @@ _PAREN_COMMENT_RE = re.compile(r'\([^)]*\)')
 # Modal G-code groups we care about.
 _MODAL_RE = re.compile(r'(?<![A-Za-z_0-9])[Gg]\s*0*(\d+(?:\.\d+)?)')
 
+# ATC pneumatics. We map a small range of user-defined M-codes onto
+# our existing HOOK: events. M100-M103 are in LinuxCNC/Buildbotics'
+# user-defined range so the planner won't error on them - but it also
+# won't *do* anything with them, so we strip them out and emit the
+# matching hook line in their place. M6 is intentionally NOT mapped:
+# users keep their own probe-and-prompt M6 override.
+#
+#   M100  DROPTOOL  (eject current tool, automatic sequence)
+#   M101  GRABTOOL  (auto-clamp on inserted holder)
+#   M102  RELEASE   (manually open collet, no clamp)
+#   M103  CLAMP     (manually close collet with bleed)
+_ATC_M_CODES = {
+    100: 'droptool',
+    101: 'grabtool',
+    102: 'release',
+    103: 'clamp',
+}
+# A token like 'M100' or 'm103', not preceded/followed by alnum.
+_ATC_M_RE = re.compile(
+    r'(?<![A-Za-z_0-9])[Mm]\s*0*(' +
+    '|'.join(str(n) for n in _ATC_M_CODES) +
+    r')(?![\w.])'
+)
+
 
 class AuxPreprocessorError(Exception):
     pass
@@ -65,9 +89,10 @@ class AuxPreprocessor(object):
     # ------------------------------------------------------------------ scan
 
     @staticmethod
-    def file_uses_w(path):
-        """Quick check: does this file contain any W-axis word? Used to skip
-        preprocessing entirely for files that don't care about W."""
+    def file_uses_aux(path):
+        """Quick check: does this file contain anything the preprocessor
+        would rewrite (W axis tokens or ATC M-codes)? Used to skip
+        preprocessing entirely for files that don't need it."""
         try:
             with open(path, 'r', encoding='utf-8', errors='replace') as f:
                 for line in f:
@@ -75,10 +100,16 @@ class AuxPreprocessor(object):
                     code = code.split(';', 1)[0]
                     if _W_TOKEN_RE.search(code):
                         return True
+                    if _ATC_M_RE.search(code):
+                        return True
         except Exception:
             pass
         return False
 
+    # Backwards-compat alias: external callers used file_uses_w before
+    # the ATC M-codes were added.
+    file_uses_w = file_uses_aux
+
     # ------------------------------------------------------------------ core
 
     def _strip_w(self, line):
@@ -139,8 +170,38 @@ class AuxPreprocessor(object):
                 # vs incremental matches what the planner sees for XYZ).
                 self._detect_modals(code, modal)
 
+                # ATC M-codes (M100-M103). Each ATC M-code on the line
+                # is replaced with its (MSG,HOOK:<event>:) line and
+                # stripped from the residual. Multiple ATC codes per
+                # line are honoured but order is left-to-right. We do
+                # this BEFORE the W-axis path so a line like
+                # "M100 W10" cleanly emits drop+move.
+                atc_matches = list(_ATC_M_RE.finditer(line))
+                if atc_matches:
+                    rewrote_any = True
+                    for m in atc_matches:
+                        try: num = int(m.group(1))
+                        except ValueError: continue
+                        event = _ATC_M_CODES.get(num)
+                        if event:
+                            fout.write('(MSG,HOOK:%s:)\n' % event)
+                    line = _ATC_M_RE.sub('', line)
+                    code = _PAREN_COMMENT_RE.sub('', line)
+                    code = code.split(';', 1)[0]
+                    # If nothing else is left on the line, we're done.
+                    if not code.strip():
+                        # Preserve any trailing comment, but skip if the
+                        # whole line is empty after the M-code strip.
+                        rest = line.rstrip()
+                        if rest:
+                            fout.write(rest + '\n')
+                        continue
+
                 if not _W_TOKEN_RE.search(code):
-                    fout.write(raw)
+                    # No W work to do; emit whatever's left after ATC
+                    # M-code stripping (or the original line if there
+                    # were no ATC codes).
+                    fout.write(line + '\n' if atc_matches else raw)
                     continue
 
                 rewrote_any = True
@@ -214,9 +275,10 @@ class AuxPreprocessor(object):
 
 
 def preprocess_file(src_path, log=None, w_first=True):
-    """Convenience: rewrite src_path in place if it uses W.
+    """Convenience: rewrite src_path in place if it uses anything the
+    preprocessor handles (W axis tokens or ATC M-codes).
     Returns True if the file was rewritten."""
-    if not AuxPreprocessor.file_uses_w(src_path):
+    if not AuxPreprocessor.file_uses_aux(src_path):
         return False
     pre = AuxPreprocessor(log=log, w_first=w_first)
     fd, tmp = tempfile.mkstemp(prefix='auxpre_', suffix='.nc',
diff --git a/src/py/bbctrl/Mach.py b/src/py/bbctrl/Mach.py
index b5a79e6..834ddaf 100644
--- a/src/py/bbctrl/Mach.py
+++ b/src/py/bbctrl/Mach.py
@@ -270,8 +270,9 @@ class Mach(Comm):
         """Apply the W-axis preprocessor to a single MDI line. Returns
         possibly-multi-line G-code with HOOK: comments inserted."""
         try:
-            from bbctrl.AuxPreprocessor import AuxPreprocessor, _W_TOKEN_RE
-            if not _W_TOKEN_RE.search(cmd):
+            from bbctrl.AuxPreprocessor import (
+                AuxPreprocessor, _W_TOKEN_RE, _ATC_M_RE)
+            if not _W_TOKEN_RE.search(cmd) and not _ATC_M_RE.search(cmd):
                 return cmd
             import io, tempfile, os
             # AuxPreprocessor.process is file-based; route through