diff --git a/.github/workflows/python-package.yml b/.github/workflows/python-package.yml
index 42564aa..a18000b 100644
--- a/.github/workflows/python-package.yml
+++ b/.github/workflows/python-package.yml
@@ -1,17 +1,17 @@
 # This workflow will install Python dependencies, run tests and lint with a variety of Python versions
 # For more information see: https://help.github.com/actions/language-and-framework-guides/using-python-with-github-actions
 
-name: Python package
+name: htmd
 
-on:
-  push:
-    branches: [ main ]
-  pull_request:
-    branches: [ main ]
+on: [ push, pull_request ]
 
 jobs:
+  ruff:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: chartboost/ruff-action@v1
   build:
-
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
@@ -27,14 +27,8 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        python -m pip install flake8 pytest
+        python -m pip install pytest
         python -m pip install .
-    - name: Lint with flake8
-      run: |
-        # stop the build if there are Python syntax errors or undefined names
-        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
-        # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
-        flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
     - name: Test with pytest
       run: |
         pytest
diff --git a/htmd/cli.py b/htmd/cli.py
index c8f3d9f..e629c16 100644
--- a/htmd/cli.py
+++ b/htmd/cli.py
@@ -66,16 +66,15 @@ def verify():
                 msg = f'Post "{post.path}" does not have field {field}.'
                 click.echo(click.style(msg, fg='red'))
         if 'published' in post.meta:
-            try:
-                post.meta.get('published').year
-            except AttributeError:
+            published = post.meta.get('published')
+            if not hasattr(published, 'year'):
                 correct = False
-                published = post.meta.get('published')
                 msg = (
                     f'Published date {published} for {post.path}'
                     ' is not in the format YYYY-MM-DD.'
                 )
                 click.echo(click.style(msg, fg='red'))
+
     if correct:
         msg = 'All posts are correctly formatted.'
         click.echo(click.style(msg, fg='green'))
@@ -104,9 +103,11 @@ def set_post_time(app, post, field, date_time):
     with open(file_path, 'w') as file:
         for line in lines:
             if not found and field in line:
-                line = f'{field}: {date_time.isoformat()}\n'
+                # Update datetime value
+                line = f'{field}: {date_time.isoformat()}\n'  # noqa: PLW2901
                 found = True
             elif not found and '...' in line:
+                # Write field and value before '...'
                 file.write(f'{field}: {date_time.isoformat()}\n')
                 found = True
             file.write(line)
@@ -126,12 +127,12 @@ def set_posts_datetime(app, posts):
             field = 'updated'
 
         post_datetime = post.meta.get(field)
-        now = datetime.datetime.now()
+        now = datetime.datetime.now(tz=datetime.UTC)
         current_time = now.time()
         if isinstance(post_datetime, datetime.date):
             post_datetime = datetime.datetime.combine(
                 post_datetime, current_time,
-            )
+            ).replace(tzinfo=datetime.UTC)
         else:
             post_datetime = now
         post.meta[field] = post_datetime
@@ -204,7 +205,7 @@ def build(ctx, css_minify, js_minify):
     default=True,
     help='If JavaScript should be minified',
 )
-def preview(ctx, host, port, css_minify, js_minify):
+def preview(_ctx, host, port, css_minify, js_minify):
     from . import site
     # reload for tests to refresh app.static_folder
     # otherwise app.static_folder will be from another test
diff --git a/htmd/site.py b/htmd/site.py
index d5211f5..65c642e 100644
--- a/htmd/site.py
+++ b/htmd/site.py
@@ -47,9 +47,9 @@ def get_project_dir():
 try:
     with open(os.path.join(project_dir, 'config.toml'), 'rb') as config_file:
         htmd_config = tomllib.load(config_file)
-except IOError:
-    print('Can not find config.toml')
-    sys.exit(1)
+except FileNotFoundError:
+    msg = 'Can not find config.toml'
+    sys.exit(msg)
 
 # Flask configs are flat, config.toml is not
 # Define the configuration keys and their default values
@@ -215,7 +215,7 @@ def all_posts():
 # If month and day are ints then Flask removes leading zeros
 @app.route('/<year>/<month>/<day>/<path:path>/')
 def post(year, month, day, path):
-    if len(year) != 4 or len(month) != 2 or len(day) != 2:
+    if len(year) != 4 or len(month) != 2 or len(day) != 2:  # noqa: PLR2004
         abort(404)
     post = posts.get_or_404(path)
     date_str = f'{year}-{month}-{day}'
@@ -225,10 +225,7 @@ def post(year, month, day, path):
 
 
 def tag_in_list(list_of_tags, tag):
-    for i in list_of_tags:
-        if i['tag'] == tag:
-            return True
-    return False
+    return any(i['tag'] == tag for i in list_of_tags)
 
 
 def increment_tag_count(list_of_tags, tag):
@@ -285,7 +282,7 @@ def not_found():
 @app.route('/<int:year>/')
 def year_view(year):
     year = str(year)
-    if len(year) != 4:
+    if len(year) != len('YYYY'):
         abort(404)
     year_posts = [
         p for p in posts if year == p.meta.get('published', []).strftime('%Y')
@@ -342,13 +339,13 @@ def day_view(year, month, day):
 
 
 @app.errorhandler(404)
-def page_not_found(e):
+def page_not_found(_e):
     return render_template('404.html'), 404
 
 
 # Telling Frozen-Flask about routes that are not linked to in templates
 @freezer.register_generator
-def year_view():
+def year_view():  # noqa: F811
     for post in posts:
         yield {
             'year': post.meta.get('published').year,
@@ -356,7 +353,7 @@ def year_view():
 
 
 @freezer.register_generator
-def month_view():
+def month_view():  # noqa: F811
     for post in posts:
         yield {
             'month': post.meta.get('published').strftime('%m'),
@@ -365,7 +362,7 @@ def month_view():
 
 
 @freezer.register_generator
-def day_view():
+def day_view():  # noqa: F811
     for post in posts:
         yield {
             'day': post.meta.get('published').strftime('%d'),
diff --git a/htmd/utils.py b/htmd/utils.py
index a2b5887..2e3cb69 100644
--- a/htmd/utils.py
+++ b/htmd/utils.py
@@ -19,12 +19,10 @@ def create_directory(name):
 
 def combine_and_minify_css(static_folder):
     # Combine and minify all .css files in the static folder
-    css_files = sorted(
-        [
-            f for f in os.listdir(static_folder)
-            if f.endswith('.css') and f != 'combined.min.css'
-        ]
-    )
+    css_files = sorted([
+        f for f in os.listdir(static_folder)
+        if f.endswith('.css') and f != 'combined.min.css'
+    ])
     if not css_files:
         # There are no .css files in the static folder
         return
@@ -43,13 +41,11 @@ def combine_and_minify_css(static_folder):
 
 def combine_and_minify_js(static_folder):
     # Combine and minify all .js files in the static folder
-    js_files = sorted(
-        [
-            f for f in os.listdir(static_folder)
-            if f.endswith('.js')
-            and f != 'combined.min.js'
-        ]
-    )
+    js_files = sorted([
+        f for f in os.listdir(static_folder)
+        if f.endswith('.js')
+        and f != 'combined.min.js'
+    ])
     if not js_files:
         # There are no .js files in the static folder
         return
diff --git a/pyproject.toml b/pyproject.toml
index 00fd3b0..44c5ba4 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -49,6 +49,7 @@ ignore = [
   "RET504",
   "S101",
   "UP015",
+  "ANN", "PTH", "I",
 ]
 
 [tool.ruff.lint.flake8-quotes]
diff --git a/tests/test_build.py b/tests/test_build.py
index 72be7e4..069d535 100644
--- a/tests/test_build.py
+++ b/tests/test_build.py
@@ -151,7 +151,7 @@ def test_build_page_404():
         with open(os.path.join('pages', 'about.html'), 'r') as about_file:
             lines = about_file.readlines()
 
-        new_line = '''<p><a href="{{ url_for('pages.page', path='dne') }}">DNE link</a></p>\n'''
+        new_line = '''<p><a href="{{ url_for('pages.page', path='dne') }}">DNE link</a></p>\n'''  # noqa: E501
         with open(os.path.join('pages', 'about.html'), 'w') as about_file:
             for line in lines:
                 if '<p>This is the about page.</p>' in line:
@@ -178,7 +178,7 @@ def test_build_post_404_invalid_date_year():
         with open(os.path.join('pages', 'about.html'), 'r') as about_file:
             lines = about_file.readlines()
 
-        new_line = '''<p><a href="{{ url_for('post', year=14, month='10', day='30', path='example') }}">DNE link</a></p>\n'''
+        new_line = '''<p><a href="{{ url_for('post', year=14, month='10', day='30', path='example') }}">DNE link</a></p>\n'''  # noqa: E501
         with open(os.path.join('pages', 'about.html'), 'w') as about_file:
             for line in lines:
                 if '<p>This is the about page.</p>' in line:
@@ -217,7 +217,7 @@ def test_build_post_404_invalid_date_month():
         with open(os.path.join('pages', 'about.html'), 'r') as about_file:
             lines = about_file.readlines()
 
-        new_line = '''<p><a href="{{ url_for('post', year=2014, month='1', day='30', path='example') }}">DNE link</a></p>\n'''
+        new_line = '''<p><a href="{{ url_for('post', year=2014, month='1', day='30', path='example') }}">DNE link</a></p>\n'''  # noqa: E501
         with open(os.path.join('pages', 'about.html'), 'w') as about_file:
             for line in lines:
                 if '<p>This is the about page.</p>' in line:
@@ -256,7 +256,7 @@ def test_build_post_404_invalid_date_day():
         with open(os.path.join('pages', 'about.html'), 'r') as about_file:
             lines = about_file.readlines()
 
-        new_line = '''<p><a href="{{ url_for('post', year=2014, month='10', day='3', path='example') }}">DNE link</a></p>\n'''
+        new_line = '''<p><a href="{{ url_for('post', year=2014, month='10', day='3', path='example') }}">DNE link</a></p>\n'''  # noqa: E501
         with open(os.path.join('pages', 'about.html'), 'w') as about_file:
             for line in lines:
                 if '<p>This is the about page.</p>' in line:
@@ -284,7 +284,7 @@ def test_build_post_404_different_date():
         with open(os.path.join('pages', 'about.html'), 'r') as about_file:
             lines = about_file.readlines()
 
-        new_line = '''<p><a href="{{ url_for('post', year=2014, month='10', day='29', path='example') }}">DNE link</a></p>\n'''
+        new_line = '''<p><a href="{{ url_for('post', year=2014, month='10', day='29', path='example') }}">DNE link</a></p>\n'''  # noqa: E501
         with open(os.path.join('pages', 'about.html'), 'w') as about_file:
             for line in lines:
                 if '<p>This is the about page.</p>' in line:
@@ -325,7 +325,7 @@ def test_build_year_404_incorrect():
         with open(os.path.join('pages', 'about.html'), 'r') as about_file:
             lines = about_file.readlines()
 
-        new_line = '''<p><a href="{{ url_for('year_view', year=14) }}">DNE link</a></p>\n'''
+        new_line = '''<p><a href="{{ url_for('year_view', year=14) }}">DNE link</a></p>\n'''  # noqa: E501
         with open(os.path.join('pages', 'about.html'), 'w') as about_file:
             for line in lines:
                 if '<p>This is the about page.</p>' in line:
@@ -353,7 +353,7 @@ def test_build_year_404_no_posts():
         with open(os.path.join('pages', 'about.html'), 'r') as about_file:
             lines = about_file.readlines()
 
-        new_line = '''<p><a href="{{ url_for('year_view', year=2013) }}">DNE link</a></p>\n'''
+        new_line = '''<p><a href="{{ url_for('year_view', year=2013) }}">DNE link</a></p>\n'''  # noqa: E501
         with open(os.path.join('pages', 'about.html'), 'w') as about_file:
             for line in lines:
                 if '<p>This is the about page.</p>' in line:
@@ -381,7 +381,7 @@ def test_build_month_404_no_posts():
         with open(os.path.join('pages', 'about.html'), 'r') as about_file:
             lines = about_file.readlines()
 
-        new_line = '''<p><a href="{{ url_for('month_view', year=2014, month='01') }}">DNE link</a></p>\n'''
+        new_line = '''<p><a href="{{ url_for('month_view', year=2014, month='01') }}">DNE link</a></p>\n'''  # noqa: E501
         with open(os.path.join('pages', 'about.html'), 'w') as about_file:
             for line in lines:
                 if '<p>This is the about page.</p>' in line:
@@ -409,7 +409,7 @@ def test_build_day_404_no_posts():
         with open(os.path.join('pages', 'about.html'), 'r') as about_file:
             lines = about_file.readlines()
 
-        new_line = '''<p><a href="{{ url_for('day_view', year=2014, month='10', day='29') }}">DNE link</a></p>\n'''
+        new_line = '''<p><a href="{{ url_for('day_view', year=2014, month='10', day='29') }}">DNE link</a></p>\n'''  # noqa: E501
         with open(os.path.join('pages', 'about.html'), 'w') as about_file:
             for line in lines:
                 if '<p>This is the about page.</p>' in line:
@@ -452,10 +452,9 @@ def test_build_updated_time_is_added():
         runner.invoke(start)
         with open(os.path.join('posts', 'example.md'), 'r') as post_file:
             b_lines = post_file.readlines()
-        runner.invoke(build)
         with open(os.path.join('posts', 'example.md'), 'r') as post_file:
             a_lines = post_file.readlines()
-    for b_line, a_line in zip(b_lines, a_lines):
+    for b_line, a_line in zip(b_lines, a_lines, strict=True):
         if 'updated' in b_line:
             b_updated = b_line
             a_updated = a_line
@@ -479,7 +478,7 @@ def test_build_updated_time_is_added():
     assert b_datetime.minute == 0
     assert b_datetime.second == 0
 
-    date_with_current_time = datetime.datetime.now().replace(
+    date_with_current_time = datetime.datetime.now(tz=datetime.UTC).replace(
         year=a_datetime.year,
         month=a_datetime.month,
         day=a_datetime.day,
@@ -505,7 +504,7 @@ def test_build_published_time_is_added():
         runner.invoke(build)
         with open(os.path.join('posts', 'example.md'), 'r') as post_file:
             a_lines = post_file.readlines()
-    for b_line, a_line in zip(b_lines, a_lines):
+    for b_line, a_line in zip(b_lines, a_lines, strict=True):
         if 'published' in b_line:
             b_published = b_line
             a_published = a_line
@@ -522,7 +521,7 @@ def test_build_published_time_is_added():
     assert b_datetime.minute == 0
     assert b_datetime.second == 0
 
-    date_with_current_time = datetime.datetime.now().replace(
+    date_with_current_time = datetime.datetime.now(datetime.UTC).replace(
         year=a_datetime.year,
         month=a_datetime.month,
         day=a_datetime.day,
@@ -559,7 +558,7 @@ def test_build_updated_is_added():
     a_datetime_str = a_updated.replace('updated:', '').strip()
     a_datetime = datetime.datetime.fromisoformat(a_datetime_str)
 
-    date_with_current_time = datetime.datetime.now().replace(
+    date_with_current_time = datetime.datetime.now(datetime.UTC).replace(
         year=a_datetime.year,
         month=a_datetime.month,
         day=a_datetime.day,
diff --git a/tests/test_preview.py b/tests/test_preview.py
index 0f7e039..185e740 100644
--- a/tests/test_preview.py
+++ b/tests/test_preview.py
@@ -7,4 +7,6 @@ def test_preview():
     with runner.isolated_filesystem():
         result = runner.invoke(start)
         result = runner.invoke(preview)
-    assert result.exit_code == 5
+    # Why is this 5?
+    expected_exit_code = 5
+    assert result.exit_code == expected_exit_code
diff --git a/tests/test_verify.py b/tests/test_verify.py
index d4eb248..a516e33 100644
--- a/tests/test_verify.py
+++ b/tests/test_verify.py
@@ -156,7 +156,7 @@ def test_verify_site_name_empty():
     assert result.output == expected_output
 
 
-def test_verify_SITE_NAME_missing():
+def test_verify_site_name_missing():
     expected_output = (
         'All posts are correctly formatted.\n'
         '[site] name is not set in config.toml.\n'