diff --git a/dev/gen_synthetic_data.py b/dev/gen_synthetic_data.py
index 73f4ac9..068824f 100644
--- a/dev/gen_synthetic_data.py
+++ b/dev/gen_synthetic_data.py
@@ -37,7 +37,7 @@ from concurrent.futures import ThreadPoolExecutor, as_completed
 
 from nanochat.common import get_base_dir
 
-api_key = open("openroutertoken.txt", 'r', encoding='utf-8').read().strip()
+api_key = open("openroutertoken.txt", "r", encoding="utf-8").read().strip()
 
 url = "https://openrouter.ai/api/v1/chat/completions"
 headers = {
@@ -45,7 +45,7 @@ headers = {
   "Content-Type": "application/json"
 }
 
-readme = open("README.md", 'r', encoding='utf-8').read().strip()
+readme = open("README.md", "r", encoding="utf-8").read().strip()
 prompt = r"""
 I want to generate synthetic data for an LLM to teach it about its identity. Here is the identity I want:
 
diff --git a/nanochat/checkpoint_manager.py b/nanochat/checkpoint_manager.py
index e1a7d91..378b0ed 100644
--- a/nanochat/checkpoint_manager.py
+++ b/nanochat/checkpoint_manager.py
@@ -34,7 +34,7 @@ def save_checkpoint(checkpoint_dir, step, model_data, optimizer_data, meta_data)
         log0(f"Saved optimizer file to: {optimizer_path}")
     # Save the metadata dict as json
     meta_path = os.path.join(checkpoint_dir, f"meta_{step:06d}.json")
-    with open(meta_path, "w", encoding='utf-8') as f:
+    with open(meta_path, "w", encoding="utf-8") as f:
         json.dump(meta_data, f, indent=2)
     log0(f"Saved metadata file to: {meta_path}")
 
@@ -50,7 +50,7 @@ def load_checkpoint(checkpoint_dir, step, device, load_optimizer=False):
         optimizer_data = torch.load(optimizer_path, map_location=device)
     # Load the metadata
     meta_path = os.path.join(checkpoint_dir, f"meta_{step:06d}.json")
-    with open(meta_path, "r", encoding='utf-8') as f:
+    with open(meta_path, "r", encoding="utf-8") as f:
         meta_data = json.load(f)
     return model_data, optimizer_data, meta_data
 
diff --git a/nanochat/report.py b/nanochat/report.py
index 2f65e9d..0b0ebd7 100644
--- a/nanochat/report.py
+++ b/nanochat/report.py
@@ -241,7 +241,7 @@ class Report:
         slug = slugify(section)
         file_name = f"{slug}.md"
         file_path = os.path.join(self.report_dir, file_name)
-        with open(file_path, "w", encoding='utf-8') as f:
+        with open(file_path, "w", encoding="utf-8") as f:
             f.write(f"## {section}\n")
             f.write(f"timestamp: {datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')}\n\n")
             for item in data:
@@ -272,11 +272,11 @@ class Report:
         final_metrics = {} # the most important final metrics we'll add as table at the end
         start_time = None
         end_time = None
-        with open(report_file, "w", encoding='utf-8') as out_file:
+        with open(report_file, "w", encoding="utf-8") as out_file:
             # write the header first
             header_file = os.path.join(report_dir, "header.md")
             if os.path.exists(header_file):
-                with open(header_file, "r", encoding='utf-8') as f:
+                with open(header_file, "r", encoding="utf-8") as f:
                     header_content = f.read()
                     out_file.write(header_content)
                     start_time = extract_timestamp(header_content, "Run started:")
@@ -293,7 +293,7 @@ class Report:
                 if not os.path.exists(section_file):
                     print(f"Warning: {section_file} does not exist, skipping")
                     continue
-                with open(section_file, "r", encoding='utf-8') as in_file:
+                with open(section_file, "r", encoding="utf-8") as in_file:
                     section = in_file.read()
                 # Extract timestamp from this section (the last section's timestamp will "stick" as end_time)
                 if "rl" not in file_name:
@@ -373,7 +373,7 @@ class Report:
         header_file = os.path.join(self.report_dir, "header.md")
         header = generate_header()
         start_time = datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
-        with open(header_file, "w", encoding='utf-8') as f:
+        with open(header_file, "w", encoding="utf-8") as f:
             f.write(header)
             f.write(f"Run started: {start_time}\n\n---\n\n")
         print(f"Reset report and wrote header to {header_file}")
diff --git a/scripts/chat_web.py b/scripts/chat_web.py
index 5d0b44a..4b67b62 100644
--- a/scripts/chat_web.py
+++ b/scripts/chat_web.py
@@ -243,7 +243,7 @@ app.add_middleware(
 async def root():
     """Serve the chat UI."""
     ui_html_path = os.path.join("nanochat", "ui.html")
-    with open(ui_html_path, "r", encoding='utf-8') as f:
+    with open(ui_html_path, "r", encoding="utf-8") as f:
         html_content = f.read()
     # Replace the API_URL to use the same origin
     html_content = html_content.replace(
diff --git a/tests/test_rustbpe.py b/tests/test_rustbpe.py
index bad3c92..aca67fc 100644
--- a/tests/test_rustbpe.py
+++ b/tests/test_rustbpe.py
@@ -455,13 +455,13 @@ def enwik8_path():
 @pytest.fixture(scope="module")
 def enwik8_small(enwik8_path):
     """Fixture providing 100KB of enwik8 for quick tests."""
-    with open(enwik8_path, "r", encoding='utf-8') as f:
+    with open(enwik8_path, "r", encoding="utf-8") as f:
         return f.read(100_000)
 
 @pytest.fixture(scope="module")
 def enwik8_large(enwik8_path):
     """Fixture providing 10MB of enwik8 for performance tests."""
-    with open(enwik8_path, "r", encoding='utf-8') as f:
+    with open(enwik8_path, "r", encoding="utf-8") as f:
         return f.read(10**7)
 
 def time_function(func, *args, **kwargs):