diff --git a/jupyter_server/prometheus/metrics.py b/jupyter_server/prometheus/metrics.py
index 3f1f7b5d7..c0aeb3756 100644
--- a/jupyter_server/prometheus/metrics.py
+++ b/jupyter_server/prometheus/metrics.py
@@ -58,9 +58,17 @@
     "Jupyter Server Extensiom Version Information",
     ["name", "version", "enabled"],
 )
-LAST_ACTIVITY = Gauge("jupyter_server_last_activity_timestamp_seconds", "Timestamp of last seen activity on this Jupyter Server")
-SERVER_STARTED = Gauge("jupyter_server_started_timestamp_seconds", "Timestamp of when this Jupyter Server was started")
-ACTIVE_DURATION = Gauge("jupyter_server_active_duration_seconds", "Number of seconds this Jupyter Server has been active")
+LAST_ACTIVITY = Gauge(
+    "jupyter_server_last_activity_timestamp_seconds",
+    "Timestamp of last seen activity on this Jupyter Server",
+)
+SERVER_STARTED = Gauge(
+    "jupyter_server_started_timestamp_seconds", "Timestamp of when this Jupyter Server was started"
+)
+ACTIVE_DURATION = Gauge(
+    "jupyter_server_active_duration_seconds",
+    "Number of seconds this Jupyter Server has been active",
+)
 
 __all__ = [
     "HTTP_REQUEST_DURATION_SECONDS",
diff --git a/jupyter_server/serverapp.py b/jupyter_server/serverapp.py
index 560c18fd3..2766509ab 100644
--- a/jupyter_server/serverapp.py
+++ b/jupyter_server/serverapp.py
@@ -110,7 +110,13 @@
     GatewaySessionManager,
 )
 from jupyter_server.log import log_request
-from jupyter_server.prometheus.metrics import SERVER_EXTENSION_INFO, SERVER_INFO, SERVER_STARTED, LAST_ACTIVITY, ACTIVE_DURATION
+from jupyter_server.prometheus.metrics import (
+    ACTIVE_DURATION,
+    LAST_ACTIVITY,
+    SERVER_EXTENSION_INFO,
+    SERVER_INFO,
+    SERVER_STARTED,
+)
 from jupyter_server.services.config import ConfigManager
 from jupyter_server.services.contents.filemanager import (
     AsyncFileContentsManager,
@@ -2712,7 +2718,11 @@ def init_metrics(self) -> None:
         SERVER_STARTED.set(started.timestamp())
 
         LAST_ACTIVITY.set_function(lambda: self.web_app.last_activity().timestamp())
-        ACTIVE_DURATION.set_function(lambda: (self.web_app.last_activity() - self.web_app.settings["started"]).total_seconds())
+        ACTIVE_DURATION.set_function(
+            lambda: (
+                self.web_app.last_activity() - self.web_app.settings["started"]
+            ).total_seconds()
+        )
 
     @catch_config_error
     def initialize(