diff --git a/python/mozbuild/mozbuild/code_analysis/mach_commands.py b/python/mozbuild/mozbuild/code_analysis/mach_commands.py
--- a/python/mozbuild/mozbuild/code_analysis/mach_commands.py
+++ b/python/mozbuild/mozbuild/code_analysis/mach_commands.py
@@ -2225,20 +2225,28 @@
         "--outgoing",
         default=False,
         action="store_true",
         help="Run clang-format on outgoing files from mercurial repository.",
     )
+    @CommandArgument(
+        "--standard-io",
+        default=False,
+        action="store_true",
+        help="Run clang-format on contents on stdin and print fixed file to stdout.",
+    )
     def clang_format(
         self,
         assume_filename,
         path,
         commit,
         output_path=None,
         output_format="diff",
         verbose=False,
         outgoing=False,
+        standard_io=False,
     ):
+
         # Run clang-format or clang-format-diff on the local changes
         # or files/directories
         if path is None and outgoing:
             repo = get_repository_object(self.topsrcdir)
             path = repo.get_outgoing_files()
@@ -2278,10 +2286,14 @@
             if rc != 0:
                 return rc
 
         if not self._is_version_eligible():
             return 1
+        
+        # Expect file on `stdin` and output formatted file to `stdout`.
+        if standard_io:
+            return self._run_clang_format_stdio(self._clang_format_path)
 
         if path is None:
             return self._run_clang_format_diff(
                 self._clang_format_diff, self._clang_format_path, commit, output
             )
@@ -2823,10 +2835,18 @@
                 if os.path.isfile(f) and f.endswith(extensions):
                     path_list.append(f)
 
         return path_list
 
+    def _run_clang_format_stdio(self, clang_format):
+        # Run clang-format on the contents of `stdin`, and print the
+        # file contents after formatting on `stdout`.
+        args = [clang_format]
+        process = subprocess.Popen(args, stdin=sys.stdin, stdout=sys.stdout)
+        return process.returncode
+
+
     def _run_clang_format_in_console(self, clang_format, paths, assume_filename):
         path_list = self._generate_path_list(assume_filename, False)
 
         if path_list == []:
             return 0