diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
new file mode 100644
index 0000000..02c88a5
--- /dev/null
+++ b/.github/workflows/release.yml
@@ -0,0 +1,17 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Create Release
+        uses: softprops/action-gh-release@v2
+        with:
+          generate_release_notes: true
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..ce11c3e
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,31 @@
+name: Test git-spell-check
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install aspell
+        run: |
+          sudo apt-get install -y aspell aspell-en
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: 3.11
+      - name: Install dependencies
+        run: pip install -r requirements.txt
+      - name: Run tests
+        run: pytest
+      - uses: compiler-research/git-spell-check@vgvassilev-patch-1
+        with:
+          debug: 1
+      - name: Setup tmate session
+        if: ${{ !cancelled() && runner.debug }}
+        uses: mxschmitt/action-tmate@v3
+        # When debugging increase to a suitable value!
+        timeout-minutes: 30
diff --git a/README.md b/README.md
index 04f4850..0d6a9d6 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,22 @@
-# git-spell-check
\ No newline at end of file
+# git-spell-check
+
+Run a spell checker **only on changed lines in pull requests**.
+
+## Features
+
+- Only checks added/modified lines
+- Ignore custom words
+- Works with any spell checker (default: `aspell`)
+- Uses GitHub annotations for inline results
+
+## Usage
+
+```yaml
+- uses: compiler-research/git-spell-check@v1
+  with:
+    base_branch: origin/master
+    include: '["**/*.md"]'
+    exclude: '["CHANGELOG.md"]'
+    cmd: "aspell list"
+    dictionary: "Compiler-Research GitHub Actions"
+```
diff --git a/action.yml b/action.yml
new file mode 100644
index 0000000..1f72907
--- /dev/null
+++ b/action.yml
@@ -0,0 +1,67 @@
+name: git-spell-check
+description: "Runs a spell checker only on the changed lines in a pull request"
+
+inputs:
+  base_branch:
+    description: "Base branch to diff against"
+    required: false
+    default: ${{ github.event.pull_request.base.ref || github.event.repository.default_branch }}
+  include:
+    description: "JSON array of glob patterns to include"
+    required: false
+    default: |
+      [
+        "**/*.md",
+        "**/*.txt",
+        "**/*.rst",
+        "**/*.json",
+        "**/*.yaml",
+        "**/*.yml",
+        "**/*.ini",
+        "**/*.tex",
+        "**/*.html",
+        "**/*.xml",
+        "**/*.xhtml",
+        "**/*.csv"
+      ]
+  exclude:
+    description: "JSON array of glob patterns to exclude"
+    required: false
+    default: '[]'
+  cmd:
+    description: "Spell checker command to run"
+    required: false
+    default: |
+      aspell --mode=sgml
+             --add-sgml-skip=code,pre,style,script,command,literal,ulink,parameter,filename,programlisting
+             --lang=en
+        list
+  dictionary:
+    description: "Custom words to ignore (space-separated)"
+    required: false
+    default: ""
+  debug:
+    description: "Debug output"
+    required: false
+    default: ${{ github.debug }}
+
+runs:
+  using: "composite"
+  steps:
+    - name: Set up Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: "3.x"
+
+    - name: Run git-spell-check
+      shell: bash
+      env: # GitHub does not pass the default values to the action script.
+        INPUT_BASE_BRANCH: ${{ inputs.base_branch }}
+        INPUT_INCLUDE: ${{ inputs.include }}
+        INPUT_EXCLUDE: ${{ inputs.exclude }}
+        INPUT_CMD: ${{ inputs.cmd }}
+        INPUT_DICTIONARY: ${{ inputs.dictionary }}
+        INPUT_DEBUG: ${{ inputs.debug }}
+      run: |
+        export
+        python ${{ github.action_path }}/git-spell-check.py
diff --git a/git-spell-check.py b/git-spell-check.py
new file mode 100755
index 0000000..9d39ad1
--- /dev/null
+++ b/git-spell-check.py
@@ -0,0 +1,186 @@
+#!/usr/bin/env python3
+import subprocess
+import os
+import sys
+import json
+import glob
+import argparse
+from pathlib import Path
+
+def parse_diff_content(diff_text):
+    """Parse unified diff content and extract changed lines with their line numbers."""
+    file_changes = {}
+    current_file = None
+    current_line = None
+
+    for line in diff_text.splitlines():
+        if line.startswith('+++'):
+            current_file = line[4:]
+            if current_file.startswith('b/'):
+                current_file = current_file[2:]
+        elif line.startswith('@@'):
+            match = next((m for m in line.split() if m.startswith('+')), None)
+            if match:
+                try:
+                    current_line = int(match.split(',')[0][1:])
+                except ValueError:
+                    current_line = None
+        elif line.startswith('+') and not line.startswith('+++'):
+            if current_file and current_line is not None:
+                file_changes.setdefault(current_file, []).append((current_line, line[1:]))
+                current_line += 1
+    return file_changes
+
+def is_detached_head():
+    """Returns True if Git is in detached HEAD state."""
+    result = subprocess.run(['git', 'symbolic-ref', '--quiet', 'HEAD'],
+                            stdout=subprocess.DEVNULL,
+                            stderr=subprocess.DEVNULL)
+    return result.returncode != 0
+
+def get_diff_files(base_branch="master", includes=None, excludes=None):
+    if is_detached_head():
+        if is_debug: print(f"Detached HEAD detected. Fetching '{base_branch}'...")
+        subprocess.run(['git', 'fetch', 'origin', base_branch], text=True)
+
+    cmd = ['git', 'diff', '--name-only', f"origin/{base_branch}"]
+    if is_debug: print(f"git diff cmd: '{cmd}'")
+    result = subprocess.run(cmd, capture_output=True, text=True)
+
+    changed_files = set(result.stdout.strip().splitlines())
+
+    if is_debug: print(f"All files '{changed_files}'")
+    # Helper to glob and normalize paths
+    def glob_relative(patterns):
+        paths = set()
+        for pattern in patterns:
+            for path in glob.glob(pattern, recursive=True):
+                try:
+                    repo_root = Path(".").resolve()
+                    rel = str(Path(path).resolve().relative_to(repo_root))
+                    paths.add(rel)
+                except ValueError:
+                    continue  # ignore files outside repo
+        return paths
+
+    included = glob_relative(includes)
+    excluded = glob_relative(excludes)
+
+    changed_files = sorted((changed_files & included) - excluded)
+    if is_debug: print(f"Filtered files {changed_files}")
+
+    return changed_files
+
+
+def get_diff_lines(file, base_branch="master"):
+    cmd = ['git', 'diff', '-U0', f"origin/{base_branch}", '--', file]
+    if is_debug: print(f"Diff cmd '{cmd}'")
+    result = subprocess.run(cmd, capture_output=True, text=True)
+    return parse_diff_content(result.stdout).get(file, [])
+
+
+def run_spell_checker(lines, cmd="aspell list", dictionary_words=None):
+    if is_debug: print(f"Aspell cmd '{cmd}'")
+    process = subprocess.Popen(cmd.split(), stdin=subprocess.PIPE, stdout=subprocess.PIPE, text=True)
+    input_text = '\n'.join([text for _, text in lines])
+    out, _ = process.communicate(input=input_text)
+    misspelled = set(out.strip().splitlines())
+    annotations = []
+    for lineno, line in lines:
+        for word in line.split():
+            clean = ''.join(filter(str.isalpha, word))
+            if clean and clean in misspelled:
+                if dictionary_words and clean in dictionary_words:
+                    continue
+                annotations.append((lineno, clean, line.strip()))
+    return annotations
+
+
+def emit_github_annotations(file, annotations):
+    for lineno, word, context in annotations:
+        print(f"::error file={file},line={lineno}::Possible typo: '{word}' in line: {context}")
+
+
+def emit_console_output(file, annotations):
+    for lineno, word, context in annotations:
+        print(f"{file}:{lineno}: typo: '{word}' in: {context}")
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Spell check only changed lines in Git diffs or a diff file."
+    )
+    parser.add_argument('--base-branch', default=os.getenv("INPUT_BASE_BRANCH",
+                                                           "master"),
+                        help='Branch to diff against (ignored if --diff-file is set)')
+    parser.add_argument('--include', default=os.getenv("INPUT_INCLUDE",
+                                                       '["**/*.md","**/*.txt",'
+                                                       '"**/*.rst","**/*.json",'
+                                                       '"**/*.yaml","**/*.yml",'
+                                                       '"**/*.ini","**/*.tex",'
+                                                       '"**/*.html","**/*.xml",'
+                                                       '"**/*.xhtml", "**/*.csv"]'),
+                        help='JSON list of glob patterns to include')
+    parser.add_argument('--exclude', default=os.getenv("INPUT_EXCLUDE", '[]'),
+                        help='JSON list of glob patterns to exclude')
+    parser.add_argument('--cmd', default=os.getenv("INPUT_CMD",
+                                                   "aspell --mode=sgml"
+                                                   "       --add-sgml-skip=code,pre,style,script,command,literal,ulink,parameter,filename,programlisting"
+                                                   "       --lang=en list"),
+                        help='Spell checker command (default: aspell list)')
+    parser.add_argument('--dictionary', default=os.getenv("INPUT_DICTIONARY", ""),
+                        help='Space-separated list of allowed words')
+    parser.add_argument('--console-output', action='store_true',
+                        help='Emit console output instead of GitHub-style error annotations')
+    parser.add_argument('--diff-file', help='Path to a unified diff file (optional)')
+    parser.add_argument("--input-string", help="Raw text string to spellcheck directly (optional)")
+    parser.add_argument("--debug", action='store_true',
+                        help="Raw text string to spellcheck directly (optional)")
+
+    args = parser.parse_args()
+
+    global is_debug
+    is_debug = os.getenv("INPUT_DEBUG") or args.debug
+
+    includes = json.loads(args.include)
+    excludes = json.loads(args.exclude)
+    dictionary_words = set(args.dictionary.split()) if args.dictionary else set()
+
+    if args.input_string:
+        lines = bytes(args.input_string, "utf-8").decode("unicode_escape")
+        if lines.lstrip().startswith('diff'):
+            file_changes = parse_diff_content(lines)
+        else:
+            file_changes = {"<stdin>": [(i + 1, line) for i, line in enumerate(lines.splitlines())]}
+    elif args.diff_file:
+        if not os.path.isfile(args.diff_file):
+            print(f"❌ Diff file not found: {args.diff_file}")
+            sys.exit(1)
+        with open(args.diff_file, 'r') as f:
+            diff_text = f.read()
+        file_changes = parse_diff_content(diff_text)
+    else:
+        files = get_diff_files(args.base_branch, includes, excludes)
+        if not files:
+            print("✅ No files to check.")
+            return
+        file_changes = {f: get_diff_lines(f, args.base_branch) for f in files}
+
+    any_issues = False
+    for file, lines in file_changes.items():
+        annotations = run_spell_checker(lines, args.cmd, dictionary_words)
+        if annotations:
+            any_issues = True
+            if args.console_output:
+                emit_console_output(file, annotations)
+            else:
+                emit_github_annotations(file, annotations)
+
+    if any_issues:
+        sys.exit(1)
+    else:
+        print("✅ No typos found.")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 0000000..fa9527e
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1,2 @@
+pytest
+
diff --git a/test/fixtures/example.diff b/test/fixtures/example.diff
new file mode 100644
index 0000000..ea3e6d2
--- /dev/null
+++ b/test/fixtures/example.diff
@@ -0,0 +1,8 @@
+diff --git a/example.md b/example.md
+index e69de29..4b825dc 100644
+--- a/example.md
++++ b/example.md
+@@ -0,2 +1,3 @@
+This should be ignored
+-Thisss should be ignored, too
++Thiss line has spelling errors.
diff --git a/test/test_spellcheck.py b/test/test_spellcheck.py
new file mode 100644
index 0000000..3fbaeae
--- /dev/null
+++ b/test/test_spellcheck.py
@@ -0,0 +1,44 @@
+import subprocess
+import tempfile
+import os
+import pytest
+from pathlib import Path
+
+SCRIPT_PATH = Path(__file__).parent.parent / "git-spell-check.py"
+
+def run_script(args=[], input_text=None):
+    cmd = ["python3", str(SCRIPT_PATH)] + args
+    result = subprocess.run(cmd, input=input_text, capture_output=True, text=True)
+    return result
+
+def test_diff_string_input():
+    example_diff = """
+diff --git a/file.md b/file.md
+index abc123..def456 100644
+--- a/file.md
++++ b/file.md
+@@ -1 +1,2 @@
+ This is a sentence with a speling mistake.
++Another bad werd here.
+"""
+    result = run_script(["--input-string", example_diff])
+    assert "speling" not in result.stdout
+    assert "werd" in result.stdout
+    assert "::error" in result.stdout  # GitHub annotation format
+
+def test_file_input(tmp_path):
+    file = Path(__file__).parent / "fixtures/example.diff"
+    result = run_script(["--diff-file", file])
+    assert "Thiss" in result.stdout
+    assert "shold" not in result.stdout
+    assert "Thisss" not in result.stdout
+
+def test_empty_string():
+    result = run_script(["--input-string", " "])
+    assert result.returncode == 0
+    assert result.stdout.strip() == "✅ No typos found."
+
+def test_help_flag():
+    result = run_script(["--help"])
+    assert result.returncode == 0
+    assert "usage" in result.stdout.lower()