diff --git a/hatch_build.py b/hatch_build.py
index 9a695be06..ab12d1b19 100644
--- a/hatch_build.py
+++ b/hatch_build.py
@@ -31,7 +31,7 @@ def initialize(self, version, build_data):
             if not os.path.exists(".git") and os.path.exists(dest):
                 # not running from git, nothing to do
                 return
-            print("Downloading CSS: %s" % url)
+            print(f"Downloading CSS: {url}")
             try:
                 css = urlopen(url).read()
             except Exception as e:
@@ -39,11 +39,11 @@ def initialize(self, version, build_data):
                 print(msg, file=sys.stderr)
 
                 if os.path.exists(dest):
-                    print("Already have CSS: %s, moving on." % dest)
+                    print(f"Already have CSS: {dest}, moving on.")
                 else:
                     raise OSError("Need CSS to proceed.")
                 return
 
             with open(dest, "wb") as f:
                 f.write(css)
-            print("Downloaded Notebook CSS to %s" % dest)
+            print(f"Downloaded Notebook CSS to {dest}")
diff --git a/tests/app/cgi-test.py b/tests/app/cgi-test.py
index 2728d67f1..8721059f1 100644
--- a/tests/app/cgi-test.py
+++ b/tests/app/cgi-test.py
@@ -10,7 +10,7 @@ def notebook_cgi_path(base_url):
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory}", *voila_args_extra]
 
 
 async def test_cgi_using_query_parameters(http_server_client, notebook_cgi_path):
diff --git a/tests/app/config_paths_test.py b/tests/app/config_paths_test.py
index 87f42484c..f412798ac 100644
--- a/tests/app/config_paths_test.py
+++ b/tests/app/config_paths_test.py
@@ -9,7 +9,7 @@
 @pytest.fixture
 def voila_config_file_paths_arg():
     path = os.path.join(BASE_DIR, "..", "configs", "general")
-    return "--VoilaTest.config_file_paths=[%r]" % path
+    return f"--VoilaTest.config_file_paths=[{path!r}]"
 
 
 def test_config_app(voila_app):
diff --git a/tests/app/contents_handler_test.py b/tests/app/contents_handler_test.py
index a8f7f75f8..afca933ec 100644
--- a/tests/app/contents_handler_test.py
+++ b/tests/app/contents_handler_test.py
@@ -15,7 +15,7 @@ def contents_prefix(base_url):
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 @pytest.fixture
diff --git a/tests/app/cwd_subdir_test.py b/tests/app/cwd_subdir_test.py
index 530f124f9..3ca173e46 100644
--- a/tests/app/cwd_subdir_test.py
+++ b/tests/app/cwd_subdir_test.py
@@ -6,12 +6,12 @@
 
 @pytest.fixture
 def cwd_subdir_notebook_url(base_url):
-    return base_url + f"voila/render/{NOTEBOOK_PATH}"
+    return f"{base_url}voila/render/{NOTEBOOK_PATH}"
 
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 async def test_hello_world(http_server_client, cwd_subdir_notebook_url):
diff --git a/tests/app/execute_cpp_test.py b/tests/app/execute_cpp_test.py
index ef3c6513b..3d2c06348 100644
--- a/tests/app/execute_cpp_test.py
+++ b/tests/app/execute_cpp_test.py
@@ -8,7 +8,7 @@
 
 @pytest.fixture
 def cpp_file_url(base_url, preheat_mode):
-    return base_url + f"voila/render/{NOTEBOOK_PATH}"
+    return f"{base_url}voila/render/{NOTEBOOK_PATH}"
 
 
 @pytest.fixture
@@ -21,7 +21,7 @@ def voila_args_extra():
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra, preheat_mode):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 @pytest.mark.skipif(
diff --git a/tests/app/nbextensions_test.py b/tests/app/nbextensions_test.py
index 24634c199..735acae4e 100644
--- a/tests/app/nbextensions_test.py
+++ b/tests/app/nbextensions_test.py
@@ -20,7 +20,7 @@ def config(app):
 def voila_config_file_paths_arg():
     # we don't want the tests to use any configuration on the system
     path = os.path.abspath(os.path.join(BASE_DIR, "../configs/general"))
-    return "--VoilaTest.config_file_paths=[%r]" % path
+    return f"--VoilaTest.config_file_paths=[{path!r}]"
 
 
 @pytest.mark.skip(reason="TODO: update for JupyterLab extensions")
diff --git a/tests/app/no_kernelspec_test.py b/tests/app/no_kernelspec_test.py
index 775fdc7d8..8f252c7fa 100644
--- a/tests/app/no_kernelspec_test.py
+++ b/tests/app/no_kernelspec_test.py
@@ -5,12 +5,12 @@
 
 @pytest.fixture
 def non_existing_kernel_notebook(base_url):
-    return base_url + f"voila/render/{NOTEBOOK_PATH}"
+    return f"{base_url}voila/render/{NOTEBOOK_PATH}"
 
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 async def test_non_existing_kernel(
diff --git a/tests/app/no_metadata.py b/tests/app/no_metadata.py
index fe8fad17a..50c1b61b0 100644
--- a/tests/app/no_metadata.py
+++ b/tests/app/no_metadata.py
@@ -10,7 +10,7 @@ def non_existing_notebook_metadata(base_url):
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 async def test_non_existing_metadata(
diff --git a/tests/app/non_existing_kernel_test.py b/tests/app/non_existing_kernel_test.py
index 079cf99a5..c16be95d4 100644
--- a/tests/app/non_existing_kernel_test.py
+++ b/tests/app/non_existing_kernel_test.py
@@ -5,12 +5,12 @@
 
 @pytest.fixture
 def non_existing_kernel_notebook(base_url):
-    return base_url + f"voila/render/{NOTEBOOK_PATH}"
+    return f"{base_url}voila/render/{NOTEBOOK_PATH}"
 
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 async def test_non_existing_kernel(http_server_client, non_existing_kernel_notebook):
diff --git a/tests/app/notebooks_test.py b/tests/app/notebooks_test.py
index 760603061..7070f68a4 100644
--- a/tests/app/notebooks_test.py
+++ b/tests/app/notebooks_test.py
@@ -11,7 +11,7 @@ def notebook_other_comms_path(base_url):
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 async def test_other_comms(http_server_client, notebook_other_comms_path):
diff --git a/tests/app/preheat_configuration_test.py b/tests/app/preheat_configuration_test.py
index 53cabe9f2..c2e9d1a86 100644
--- a/tests/app/preheat_configuration_test.py
+++ b/tests/app/preheat_configuration_test.py
@@ -13,7 +13,7 @@
 @pytest.fixture
 def voila_config_file_paths_arg():
     path = os.path.join(BASE_DIR, "..", "configs", "preheat")
-    return "--VoilaTest.config_file_paths=[%r]" % path
+    return f"--VoilaTest.config_file_paths=[{path!r}]"
 
 
 @pytest.fixture
diff --git a/tests/app/preheat_multiple_notebooks_test.py b/tests/app/preheat_multiple_notebooks_test.py
index 8e34f6131..bd395a2f2 100644
--- a/tests/app/preheat_multiple_notebooks_test.py
+++ b/tests/app/preheat_multiple_notebooks_test.py
@@ -13,7 +13,7 @@
 @pytest.fixture
 def voila_config_file_paths_arg():
     path = os.path.join(BASE_DIR, "..", "configs", "preheat")
-    return "--VoilaTest.config_file_paths=[%r]" % path
+    return f"--VoilaTest.config_file_paths=[{path!r}]"
 
 
 @pytest.fixture
diff --git a/tests/app/serve_directory_test.py b/tests/app/serve_directory_test.py
index bac1d5146..a3e75e968 100644
--- a/tests/app/serve_directory_test.py
+++ b/tests/app/serve_directory_test.py
@@ -13,7 +13,7 @@ def preheat_mode():
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 async def test_print(http_server_client, print_notebook_url):
diff --git a/tests/app/show_traceback_test.py b/tests/app/show_traceback_test.py
index bcdd8353e..cea9796f4 100644
--- a/tests/app/show_traceback_test.py
+++ b/tests/app/show_traceback_test.py
@@ -16,7 +16,7 @@ def notebook_show_traceback_path(base_url):
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra, show_tracebacks):
     return [
-        "--VoilaTest.root_dir=%r" % notebook_directory,
+        f"--VoilaTest.root_dir={notebook_directory!r}",
         f"--VoilaConfiguration.show_tracebacks={show_tracebacks}",
         *voila_args_extra,
     ]
diff --git a/tests/app/template_cli_test.py b/tests/app/template_cli_test.py
index acd140e7d..bb2bbefb3 100644
--- a/tests/app/template_cli_test.py
+++ b/tests/app/template_cli_test.py
@@ -18,9 +18,7 @@ def voila_args_extra():
     )
     return [
         "--template=test_template",
-        "--VoilaTest.template_paths=[{!r}, {!r}]".format(
-            path_test_template, path_default
-        ),
+        f"--VoilaTest.template_paths=[{path_test_template!r}, {path_default!r}]",
         "--VoilaExecutor.timeout=240",
     ]
 
diff --git a/tests/app/tree_test.py b/tests/app/tree_test.py
index 70c063690..c1f350277 100644
--- a/tests/app/tree_test.py
+++ b/tests/app/tree_test.py
@@ -9,7 +9,7 @@ def preheat_mode():
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 @pytest.fixture
diff --git a/tests/conftest.py b/tests/conftest.py
index b56e6411e..3a66e3233 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -19,7 +19,7 @@ def notebook_directory():
 
 @pytest.fixture
 def print_notebook_url(base_url):
-    return base_url + "voila/render/print.ipynb"
+    return f"{base_url}voila/render/print.ipynb"
 
 
 @pytest.fixture
diff --git a/tests/server/cwd_subdir_test.py b/tests/server/cwd_subdir_test.py
index 35b9f4271..7ee0e95fa 100644
--- a/tests/server/cwd_subdir_test.py
+++ b/tests/server/cwd_subdir_test.py
@@ -5,12 +5,12 @@
 
 @pytest.fixture
 def cwd_subdir_notebook_url(base_url):
-    return base_url + "voila/render/subdir/cwd_subdir.ipynb"
+    return f"{base_url}voila/render/subdir/cwd_subdir.ipynb"
 
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 async def test_hello_world(http_server_client, cwd_subdir_notebook_url):
diff --git a/tests/server/execute_cpp_test.py b/tests/server/execute_cpp_test.py
index 168b02f0e..727d43eff 100644
--- a/tests/server/execute_cpp_test.py
+++ b/tests/server/execute_cpp_test.py
@@ -7,7 +7,7 @@
 
 @pytest.fixture
 def cpp_file_url(base_url):
-    return base_url + "voila/render/print.xcpp"
+    return f"{base_url}voila/render/print.xcpp"
 
 
 @pytest.fixture
@@ -17,7 +17,7 @@ def jupyter_server_args_extra():
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 @pytest.mark.skipif(
diff --git a/tests/server/tree_test.py b/tests/server/tree_test.py
index d660bbf49..d7b3660ea 100644
--- a/tests/server/tree_test.py
+++ b/tests/server/tree_test.py
@@ -4,7 +4,7 @@
 
 @pytest.fixture
 def voila_args(notebook_directory, voila_args_extra):
-    return ["--VoilaTest.root_dir=%r" % notebook_directory, *voila_args_extra]
+    return [f"--VoilaTest.root_dir={notebook_directory!r}", *voila_args_extra]
 
 
 @pytest.fixture
@@ -16,7 +16,7 @@ def jupyter_server_args_extra():
 
 
 async def test_tree(http_server_client, base_url):
-    response = await http_server_client.fetch(base_url + "voila/tree")
+    response = await http_server_client.fetch(f"{base_url}voila/tree")
     assert response.code == 200
     text = response.body.decode("utf-8")
     assert "print.ipynb" in text, "tree handler should render ipynb files"
diff --git a/voila/app.py b/voila/app.py
index 3ca9b22a6..24724effd 100644
--- a/voila/app.py
+++ b/voila/app.py
@@ -387,7 +387,10 @@ def display_url(self):
             if not url.endswith("/"):
                 url += "/"
         else:
-            ip = "%s" % socket.gethostname() if self.ip in ("", "0.0.0.0") else self.ip
+            if self.ip in ("", "0.0.0.0"):
+                ip = socket.gethostname()
+            else:
+                ip = self.ip
             url = self._url(ip)
         # TODO: do we want to have the token?
         if self.identity_provider.token:
@@ -411,7 +414,7 @@ def _url(self, ip):
         # TODO: https / certfile
         # proto = 'https' if self.certfile else 'http'
         proto = "http"
-        return "%s://%s:%i%s" % (proto, ip, self.port, self.base_url)
+        return f"{proto}://{ip}:{self.port}{self.base_url}"
 
     config_file_paths = List(
         Unicode(), config=True, help=_("Paths to search for voila.(py|json)")
@@ -526,10 +529,10 @@ def initialize(self, argv=None):
                     self.notebook_path = arg
                 else:
                     raise ValueError(
-                        "argument is neither a file nor a directory: %r" % arg
+                        f"argument is neither a file nor a directory: {arg!r}"
                     )
         elif len(self.extra_args) != 0:
-            raise ValueError("provided more than 1 argument: %r" % self.extra_args)
+            raise ValueError(f"provided more than 1 argument: {self.extra_args!r}")
 
         # then we load the config
         self.load_config_file("voila", path=self.config_file_paths)
@@ -569,7 +572,7 @@ def setup_template_dirs(self):
         self.log.debug("template paths:\n\t%s", "\n\t".join(self.template_paths))
         self.log.debug("static paths:\n\t%s", "\n\t".join(self.static_paths))
         if self.notebook_path and not os.path.exists(self.notebook_path):
-            raise ValueError("Notebook not found: %s" % self.notebook_path)
+            raise ValueError(f"Notebook not found: {self.notebook_path}")
 
     def init_settings(self) -> Dict:
         """Initialize settings for Voila application."""
@@ -684,14 +687,12 @@ def init_handlers(self) -> List:
         handlers.extend(
             [
                 (
-                    url_path_join(
-                        self.server_url, r"/api/kernels/%s" % _kernel_id_regex
-                    ),
+                    url_path_join(self.server_url, rf"/api/kernels/{_kernel_id_regex}"),
                     KernelHandler,
                 ),
                 (
                     url_path_join(
-                        self.server_url, r"/api/kernels/%s/channels" % _kernel_id_regex
+                        self.server_url, rf"/api/kernels/{_kernel_id_regex}/channels"
                     ),
                     KernelWebsocketHandler,
                 ),
@@ -724,9 +725,7 @@ def init_handlers(self) -> List:
         if self.voila_configuration.preheat_kernel:
             handlers.append(
                 (
-                    url_path_join(
-                        self.server_url, r"/voila/query/%s" % _kernel_id_regex
-                    ),
+                    url_path_join(self.server_url, rf"/voila/query/{_kernel_id_regex}"),
                     RequestInfoSocketHandler,
                 )
             )
@@ -775,7 +774,7 @@ def init_handlers(self) -> List:
                 [
                     (self.server_url, TornadoVoilaTreeHandler, tree_handler_conf),
                     (
-                        url_path_join(self.server_url, r"/voila/tree" + path_regex),
+                        url_path_join(self.server_url, rf"/voila/tree{path_regex}"),
                         TornadoVoilaTreeHandler,
                         tree_handler_conf,
                     ),
@@ -792,7 +791,7 @@ def init_handlers(self) -> List:
                     # On serving a directory, expose the content handler.
                     (
                         url_path_join(
-                            self.server_url, r"/voila/api/contents%s" % path_regex
+                            self.server_url, rf"/voila/api/contents{path_regex}"
                         ),
                         VoilaContentsHandler,
                         tree_handler_conf,
diff --git a/voila/execute.py b/voila/execute.py
index 6071725ee..e7f393908 100644
--- a/voila/execute.py
+++ b/voila/execute.py
@@ -118,9 +118,7 @@ def strip_code_cell_errors(self, cell):
             output for output in outputs if output["output_type"] == "error"
         ]
 
-        error_message = "There was an error when executing cell [{}]. {}".format(
-            cell["execution_count"], self.cell_error_instruction
-        )
+        error_message = f'There was an error when executing cell [{cell["execution_count"]}]. {self.cell_error_instruction}'
 
         for output in error_outputs:
             output["ename"] = "ExecutionError"
diff --git a/voila/notebook_renderer.py b/voila/notebook_renderer.py
index 2ba094e59..079b8bb5f 100644
--- a/voila/notebook_renderer.py
+++ b/voila/notebook_renderer.py
@@ -397,5 +397,5 @@ async def find_kernel_name_for_language(self, kernel_language, kernel_specs=None
             return matches[0]
         else:
             raise tornado.web.HTTPError(
-                500, "No Jupyter kernel for language %r found" % kernel_language
+                500, f"No Jupyter kernel for language {kernel_language!r} found"
             )
diff --git a/voila/server_extension.py b/voila/server_extension.py
index 959990c05..d57253088 100644
--- a/voila/server_extension.py
+++ b/voila/server_extension.py
@@ -120,7 +120,7 @@ def _load_jupyter_server_extension(server_app):
                 },
             ),
             (
-                url_path_join(base_url, r"/voila/api/contents%s" % path_regex),
+                url_path_join(base_url, rf"/voila/api/contents{path_regex}"),
                 VoilaContentsHandler,
                 tree_handler_conf,
             ),
diff --git a/voila/tornado/contentshandler.py b/voila/tornado/contentshandler.py
index b49dfc3e3..3665ed861 100644
--- a/voila/tornado/contentshandler.py
+++ b/voila/tornado/contentshandler.py
@@ -34,10 +34,10 @@ async def get(self, path=""):
 
         format = self.get_query_argument("format", default=None)
         if format not in {None, "text", "base64"}:
-            raise web.HTTPError(400, "Format %r is invalid" % format)
+            raise web.HTTPError(400, f"Format {format!r} is invalid")
         content_str = self.get_query_argument("content", default="1")
         if content_str not in {"0", "1"}:
-            raise web.HTTPError(400, "Content %r is invalid" % content_str)
+            raise web.HTTPError(400, f"Content {content_str!r} is invalid")
         content = int(content_str or "")
 
         if not cm.allow_hidden and await ensure_async(cm.is_hidden(path)):
diff --git a/voila/utils.py b/voila/utils.py
index 7100a02af..d40134e61 100644
--- a/voila/utils.py
+++ b/voila/utils.py
@@ -74,7 +74,7 @@ def get_server_root_dir(settings):
     home = os.path.expanduser("~")
     if root_dir.startswith(home + os.path.sep):
         # collapse $HOME to ~
-        root_dir = "~" + root_dir[len(home) :]
+        root_dir = f"~{root_dir[len(home):]}"
     return root_dir