diff --git a/hook_launcher.py b/hook_launcher.py
index a4c0b3e..39fc835 100755
--- a/hook_launcher.py
+++ b/hook_launcher.py
@@ -1,3 +1,4 @@
 #!/usr/bin/env python3
 from nyacme.hook import main
+
 main()
diff --git a/nyacme/__main__.py b/nyacme/__main__.py
index fb646d5..000f235 100644
--- a/nyacme/__main__.py
+++ b/nyacme/__main__.py
@@ -1,8 +1,8 @@
 import argparse
-import os.path
-import subprocess
 import logging
+import os.path
 import shutil
+import subprocess
 from datetime import datetime
 from pathlib import Path
 
@@ -35,7 +35,8 @@ def main() -> None:
 
         cert_path = output_dir / domain / 'cert.pem'
         if cert_path.is_file():
-            out = subprocess.run([ 'openssl', 'x509', '-enddate', '-noout', '-in', cert_path ], stdout=subprocess.PIPE, check=True).stdout.decode('utf-8').strip()
+            cmd = [ 'openssl', 'x509', '-enddate', '-noout', '-in', cert_path ]
+            out = subprocess.run(cmd, stdout=subprocess.PIPE, check=True).stdout.decode('utf-8').strip()
             date = datetime.strptime(out, 'notAfter=%b %d %H:%M:%S %Y %Z')
             # if more than 1 month, skip
             delta = date - datetime.now()
diff --git a/nyacme/config.py b/nyacme/config.py
index 0848982..dd6d7ce 100644
--- a/nyacme/config.py
+++ b/nyacme/config.py
@@ -1,8 +1,9 @@
-from typing import Optional
-import tomllib
 import logging
-import sys
 import os
+import sys
+from typing import Optional
+
+import tomllib
 
 log = logging.getLogger(__name__)
 
diff --git a/nyacme/handlers/base.py b/nyacme/handlers/base.py
index 356b852..09147c1 100644
--- a/nyacme/handlers/base.py
+++ b/nyacme/handlers/base.py
@@ -2,6 +2,7 @@ import logging
 
 from ..config import Config
 
+
 class Handler:
     zone: str
     config: Config
diff --git a/nyacme/handlers/hetzner.py b/nyacme/handlers/hetzner.py
index 609b248..546efba 100644
--- a/nyacme/handlers/hetzner.py
+++ b/nyacme/handlers/hetzner.py
@@ -1,9 +1,10 @@
-import urllib.request
 import json
-from typing import Optional, Any
+import urllib.request
+from typing import Any, Optional
 
-from .base import Handler
 from ..config import Config
+from .base import Handler
+
 
 class HetznerHandler(Handler):
     # discovered
@@ -41,7 +42,7 @@ class HetznerHandler(Handler):
                 raise Exception(json.loads(res)['error'])
             except Exception:
                 raise Exception(res)
- 
+
     def create(self, record_name: str, record_value: str) -> None:
         self.remove(record_name)
         self.log.info('creating %s with value %s', record_name, record_value)
diff --git a/nyacme/handlers/http.py b/nyacme/handlers/http.py
index 2495b69..5c505ce 100644
--- a/nyacme/handlers/http.py
+++ b/nyacme/handlers/http.py
@@ -1,7 +1,8 @@
 import os
 
-from .base import Handler
 from ..config import Config
+from .base import Handler
+
 
 class HTTPHandler(Handler):
     def __init__(self, zone: str, config: Config, token: str) -> None:
diff --git a/nyacme/hook.py b/nyacme/hook.py
index ba196f2..5f203a1 100644
--- a/nyacme/hook.py
+++ b/nyacme/hook.py
@@ -1,15 +1,14 @@
 import argparse
 import logging
-from itertools import chain
-import time
 import sys
+import time
+from itertools import chain
 
 import dns.resolver
 
 from .config import read_config
 from .handlers import HetznerHandler
 
-
 logging.basicConfig(level=logging.INFO, format='> [%(levelname)s] %(name)s: %(message)s')
 log = logging.getLogger('nyacme_hook')
 
@@ -49,7 +48,9 @@ def main() -> None:
 
     if args.type == 'dns-01':
         resolver = dns.resolver.Resolver('', configure=False)
-        resolver.nameservers = list(chain.from_iterable(list(map(resolve4, handler.nameservers)) + list(map(resolve6, handler.nameservers))))
+        ns4 = list(map(resolve4, handler.nameservers))
+        ns6 = list(map(resolve6, handler.nameservers))
+        resolver.nameservers = list(chain.from_iterable(ns4 + ns6))
         for i in range(5):
             log.info('checking DNS (attempt %d/5)', i+1)
             try:
diff --git a/ruff.toml b/ruff.toml
new file mode 100644
index 0000000..a9fbb4a
--- /dev/null
+++ b/ruff.toml
@@ -0,0 +1,22 @@
+line-length = 120
+
+# https://docs.astral.sh/ruff/rules/
+[lint]
+extend-select = [
+    "Q", # quotes
+    "PT", # pytest
+    "I", # isort
+    "F", # pyflakes
+    "E", # pycodestyle (errors)
+    "W", # pycodestyle (warnings)
+    "UP", # pyupgrade
+    "ISC", # implicit string concat
+
+    "T20", # no print/pprint
+    "G001", # no str.format in logging
+    "C901", # check for complexity
+]
+
+[lint.flake8-quotes]
+inline-quotes = "single"
+docstring-quotes = "single"