diff --git a/.github/workflows/bin/spack-labeler.py b/.github/workflows/bin/spack-labeler.py
index b68124c3085..209fb0d1293 100755
--- a/.github/workflows/bin/spack-labeler.py
+++ b/.github/workflows/bin/spack-labeler.py
@@ -28,21 +28,45 @@ def import_labels_config(path: str):
 
 
 def main():
+    # Validate required environment variables
+    required_vars = ["LABELS_CONFIG", "GH_REPO", "GH_PR_NUMBER"]
+    missing_vars = [var for var in required_vars if var not in os.environ]
+    if missing_vars:
+        raise Exception(f"Missing required environment variables: {', '.join(missing_vars)}")
+
     labels_config_path = os.environ["LABELS_CONFIG"]
     repository = os.environ["GH_REPO"]
     pr_number = os.environ["GH_PR_NUMBER"]
-    token = os.environ["GH_TOKEN"]
+    token = os.environ.get("GH_TOKEN", "")
 
-    headers = {"Accept": "application/vnd.github+json"}
+    headers = {"Accept": "application/vnd.github+json", "User-Agent": "spack-labeler"}
     if token:
         headers["Authorization"] = f"Bearer {token}"
 
     label_patterns = import_labels_config(labels_config_path)
 
+    # use a requests session to attempt to retry failed requests if the GitHub API fails
+    session = requests.Session()
+    retries = requests.adapters.Retry(
+        total=3, backoff_factor=1, status_forcelist=[500, 502, 503, 504]
+    )
+    session.mount("https://", requests.adapters.HTTPAdapter(max_retries=retries))
+
     url = f"https://api.github.com/repos/{repository}/pulls/{pr_number}"
-    pull_request = requests.get(url, headers=headers).json()
+    pull_request_resp = session.get(url, headers=headers, timeout=30)
+    if pull_request_resp.status_code != 200:
+        raise Exception(
+            f"Failed to query GitHub API for PR info [{pull_request_resp.status_code}]: "
+            f"{pull_request_resp.text}"
+        )
 
-    pull_request_files = requests.get(url + "/files", headers=headers)
+    pull_request = pull_request_resp.json()
+    pull_request_files = session.get(url + "/files", headers=headers, timeout=30)
+    if pull_request_files.status_code != 200:
+        raise Exception(
+            f"Failed to query GitHub API for PR files [{pull_request_files.status_code}]: "
+            f"{pull_request_files.text}"
+        )
 
     labels = set()
 
@@ -57,7 +81,7 @@ def main():
         # the corresponding labels.
         for label, pattern_dict in label_patterns.items():
             attr_matches = []
-            # Pattern matches for for each attribute are or'd together
+            # Pattern matches for each attribute are or'd together
             for attr, patterns in pattern_dict.items():
                 # 'patch' is an example of an attribute that is not required to
                 # appear in response when listing pull request files.  See here:
@@ -78,6 +102,9 @@ def main():
     # Maintain non-managed labels (i.e. those that are not in label_patterns)
     labels.update(existing_labels.difference(label_patterns))
 
+    if not token:
+        print("Warning: No GH_TOKEN defined, performing a local dry run only")
+
     if existing_labels == labels:
         print(f"[PR #{pr_number}]: labels already up-to-date")
         return
@@ -91,10 +118,11 @@ def main():
         print(f"[PR #{pr_number}]: Removing label(s): [{'] ['.join(removed_labels)}]")
 
     if token:
-        resp = requests.put(
+        resp = session.put(
             f"https://api.github.com/repos/{repository}/issues/{pr_number}/labels",
             json={"labels": list(labels)},
             headers=headers,
+            timeout=30,
         )
         resp.raise_for_status()