diff --git a/README.md b/README.md
index 68bb0eb..c19c281 100644
--- a/README.md
+++ b/README.md
@@ -44,6 +44,9 @@ You can sponsor me [here](https://github.com/sponsors/jidicula)!
 * `include-regex` [optional]: A regex to include files or directories that should be checked.
   * Default: `^.*\.((((c|C)(c|pp|xx|\+\+)?$)|((h|H)h?(pp|xx|\+\+)?$))|(ino|pde|proto|cu))$`
   * Pattern matching is done with a POSIX `grep -E` extended regex, **not** a glob expression. You can exclude multiple patterns like this: `(hello|world)`. Build and verify your regex at https://regex101.com .
+* `changed-only` [optional]: check only changed lines in commit.
+  * Default: `false`
+  * Available values: `true`, `false`
 
 This action checks all C/C++/Protobuf (including Arduino `.ino` and `.pde`) files in the provided directory in the GitHub workspace are formatted correctly using `clang-format`. If no directory is provided or the provided path is not a directory in the GitHub workspace, all C/C++/Protobuf files are checked.
 
diff --git a/action.yml b/action.yml
index 26fe4d0..b30c105 100644
--- a/action.yml
+++ b/action.yml
@@ -26,12 +26,15 @@ inputs:
     description: 'A regex to override the C/C++/Protobuf/CUDA filetype regex. that should be checked. Default results in the regex defined in `check.sh`.'
     required: false
     default: ''
-
+  changed-only:
+    description: 'Check only changed lines at files modified in commit.'
+    required: false
+    default: 'false'
 runs:
   using: "composite"
   steps:
     - run: |
-        "${{ github.action_path }}/check.sh" "${{ inputs.clang-format-version }}" "${{ inputs.check-path }}" "${{ inputs.fallback-style }}" "${{ inputs.exclude-regex }}" "${{ inputs.include-regex }}"
+        "${{ github.action_path }}/check.sh" "${{ inputs.clang-format-version }}" "${{ inputs.check-path }}" "${{ inputs.fallback-style }}" "${{ inputs.exclude-regex }}" "${{ inputs.include-regex }}" "${{ inputs.changed-only }}"
       shell: bash
     - name: Save PR head commit SHA
       if: failure() && github.event_name == 'pull_request'
diff --git a/check.sh b/check.sh
index 4ea3929..18b60d8 100755
--- a/check.sh
+++ b/check.sh
@@ -41,15 +41,29 @@ format_diff() {
 	return 0
 }
 
+diff_only() {
+	formatted="$(git diff -U0 --no-color --relative HEAD^ | \
+		docker run -i -v "$(pwd)":"$(pwd)" -w "$(pwd)" \
+			--rm ghcr.io/jidicula/clang-format:"$CLANG_FORMAT_MAJOR_VERSION" \
+			/usr/bin/clang-format-diff -p1 -style=file -fallback-style="$FALLBACK_STYLE" \
+			-iregex "$INCLUDE_REGEX")"
+	[[ -n $formatted ]] && exit_code=1
+}
+
 CLANG_FORMAT_MAJOR_VERSION="$1"
 CHECK_PATH="$2"
 FALLBACK_STYLE="$3"
 EXCLUDE_REGEX="$4"
 INCLUDE_REGEX="$5"
+CHANGED_ONLY="$6"
 
 # Set the regex to an empty string regex if nothing was provided
 if [[ -z $EXCLUDE_REGEX ]]; then
 	EXCLUDE_REGEX="^$"
+else
+	if [[ $CHANGED_ONLY != false ]]; then
+		echo "exclude-regex option will be ignored" >&2
+	fi
 fi
 
 # Set the filetype regex if nothing was provided.
@@ -73,18 +87,21 @@ fi
 # initialize exit code
 exit_code=0
 
-# All files improperly formatted will be printed to the output.
-src_files=$(find "$CHECK_PATH" -name .git -prune -o -regextype posix-egrep -regex "$INCLUDE_REGEX" -print)
-
-# check formatting in each source file
-IFS=$'\n' # Loop below should separate on new lines, not spaces.
-for file in $src_files; do
-	# Only check formatting if the path doesn't match the regex
-	if ! [[ ${file} =~ $EXCLUDE_REGEX ]]; then
-		format_diff "${file}"
-	fi
-done
+if [[ $CHANGED_ONLY == false ]]; then
+	# All files improperly formatted will be printed to the output.
+	src_files=$(find "$CHECK_PATH" -name .git -prune -o -regextype posix-egrep -regex "$INCLUDE_REGEX" -print)
 
+	# check formatting in each source file
+	IFS=$'\n' # Loop below should separate on new lines, not spaces.
+	for file in $src_files; do
+		# Only check formatting if the path doesn't match the regex
+		if ! [[ ${file} =~ $EXCLUDE_REGEX ]]; then
+			format_diff "${file}"
+		fi
+	done
+else
+	diff_only
+fi
 # global exit code is flipped to nonzero if any invocation of `format_diff` has
 # a formatting difference.
 exit "$exit_code"