diff --git a/src/apm_cli/config.py b/src/apm_cli/config.py
index 0d453221..75028adf 100644
--- a/src/apm_cli/config.py
+++ b/src/apm_cli/config.py
@@ -16,7 +16,7 @@ def ensure_config_exists():
         os.makedirs(CONFIG_DIR)
 
     if not os.path.exists(CONFIG_FILE):
-        with open(CONFIG_FILE, "w") as f:
+        with open(CONFIG_FILE, "w", encoding="utf-8") as f:
             json.dump({"default_client": "vscode"}, f)
 
 
@@ -32,7 +32,7 @@ def get_config():
     if _config_cache is not None:
         return _config_cache
     ensure_config_exists()
-    with open(CONFIG_FILE, "r") as f:
+    with open(CONFIG_FILE, "r", encoding="utf-8") as f:
         _config_cache = json.load(f)
     return _config_cache
 
@@ -53,7 +53,7 @@ def update_config(updates):
     config = get_config()
     config.update(updates)
 
-    with open(CONFIG_FILE, "w") as f:
+    with open(CONFIG_FILE, "w", encoding="utf-8") as f:
         json.dump(config, f, indent=2)
     _invalidate_config_cache()
 
diff --git a/src/apm_cli/marketplace/client.py b/src/apm_cli/marketplace/client.py
index 6fba4edf..5d6da1e0 100644
--- a/src/apm_cli/marketplace/client.py
+++ b/src/apm_cli/marketplace/client.py
@@ -83,13 +83,13 @@ def _read_cache(name: str) -> Optional[Dict]:
     if not os.path.exists(data_path) or not os.path.exists(meta_path):
         return None
     try:
-        with open(meta_path, "r") as f:
+        with open(meta_path, "r", encoding="utf-8") as f:
             meta = json.load(f)
         fetched_at = meta.get("fetched_at", 0)
         ttl = meta.get("ttl_seconds", _CACHE_TTL_SECONDS)
         if time.time() - fetched_at > ttl:
             return None  # Expired
-        with open(data_path, "r") as f:
+        with open(data_path, "r", encoding="utf-8") as f:
             return json.load(f)
     except (json.JSONDecodeError, OSError, KeyError) as exc:
         logger.debug("Cache read failed for '%s': %s", name, exc)
@@ -102,7 +102,7 @@ def _read_stale_cache(name: str) -> Optional[Dict]:
     if not os.path.exists(data_path):
         return None
     try:
-        with open(data_path, "r") as f:
+        with open(data_path, "r", encoding="utf-8") as f:
             return json.load(f)
     except (json.JSONDecodeError, OSError):
         return None
@@ -113,9 +113,9 @@ def _write_cache(name: str, data: Dict) -> None:
     data_path = _cache_data_path(name)
     meta_path = _cache_meta_path(name)
     try:
-        with open(data_path, "w") as f:
+        with open(data_path, "w", encoding="utf-8") as f:
             json.dump(data, f, indent=2)
-        with open(meta_path, "w") as f:
+        with open(meta_path, "w", encoding="utf-8") as f:
             json.dump(
                 {"fetched_at": time.time(), "ttl_seconds": _CACHE_TTL_SECONDS},
                 f,
diff --git a/src/apm_cli/marketplace/registry.py b/src/apm_cli/marketplace/registry.py
index 3aa668d5..4ddab2dd 100644
--- a/src/apm_cli/marketplace/registry.py
+++ b/src/apm_cli/marketplace/registry.py
@@ -30,7 +30,7 @@ def _ensure_file() -> str:
     ensure_config_exists()
     path = _marketplaces_path()
     if not os.path.exists(path):
-        with open(path, "w") as f:
+        with open(path, "w", encoding="utf-8") as f:
             json.dump({"marketplaces": []}, f, indent=2)
     return path
 
@@ -48,7 +48,7 @@ def _load() -> List[MarketplaceSource]:
 
     path = _ensure_file()
     try:
-        with open(path, "r") as f:
+        with open(path, "r", encoding="utf-8") as f:
             data = json.load(f)
     except (json.JSONDecodeError, OSError) as exc:
         logger.warning("Failed to read %s: %s", path, exc)
@@ -71,7 +71,7 @@ def _save(sources: List[MarketplaceSource]) -> None:
     path = _ensure_file()
     data = {"marketplaces": [s.to_dict() for s in sources]}
     tmp = path + ".tmp"
-    with open(tmp, "w") as f:
+    with open(tmp, "w", encoding="utf-8") as f:
         json.dump(data, f, indent=2)
     os.replace(tmp, path)
     _registry_cache = list(sources)
diff --git a/src/apm_cli/models/plugin.py b/src/apm_cli/models/plugin.py
index aa486d37..40eba1cb 100644
--- a/src/apm_cli/models/plugin.py
+++ b/src/apm_cli/models/plugin.py
@@ -108,7 +108,7 @@ def from_path(cls, plugin_path: Path) -> "Plugin":
         if metadata_file is None:
             raise FileNotFoundError(f"Plugin metadata not found in any expected location: {plugin_path}")
         
-        with open(metadata_file, "r") as f:
+        with open(metadata_file, "r", encoding="utf-8") as f:
             metadata_dict = json.load(f)
         
         metadata = PluginMetadata.from_dict(metadata_dict)
diff --git a/src/apm_cli/runtime/copilot_runtime.py b/src/apm_cli/runtime/copilot_runtime.py
index 485057f1..39bee709 100644
--- a/src/apm_cli/runtime/copilot_runtime.py
+++ b/src/apm_cli/runtime/copilot_runtime.py
@@ -200,7 +200,7 @@ def get_mcp_servers(self) -> Dict[str, Any]:
             return {}
         
         try:
-            with open(mcp_config_path, 'r') as f:
+            with open(mcp_config_path, 'r', encoding="utf-8") as f:
                 config = json.load(f)
                 return config.get('servers', {})
         except Exception as e: