diff --git a/hyperliquid/api.py b/hyperliquid/api.py
index d808f2c..6416acb 100644
--- a/hyperliquid/api.py
+++ b/hyperliquid/api.py
@@ -3,6 +3,7 @@
 from json import JSONDecodeError
 
 import requests
+from requests.exceptions import RequestException
 
 from hyperliquid.utils.constants import MAINNET_API_URL
 from hyperliquid.utils.error import ClientError, ServerError
@@ -10,34 +11,102 @@
 
 
 class API:
-    def __init__(self, base_url=None, timeout=None):
+    """
+    A base client class for interacting with the Hyperliquid REST API.
+    Handles session management, requests, and comprehensive error handling.
+    """
+    def __init__(self, base_url: str = None, timeout: float = None):
+        """
+        Initializes the API client.
+        :param base_url: The base URL for the API. Defaults to MAINNET_API_URL.
+        :param timeout: The request timeout in seconds.
+        """
         self.base_url = base_url or MAINNET_API_URL
+        self.timeout = timeout
+        
+        # Initialize the session for connection pooling and header persistence.
         self.session = requests.Session()
         self.session.headers.update({"Content-Type": "application/json"})
         self._logger = logging.getLogger(__name__)
-        self.timeout = timeout
 
     def post(self, url_path: str, payload: Any = None) -> Any:
+        """
+        Sends a POST request to the specified API endpoint.
+        :param url_path: The endpoint path (e.g., '/info').
+        :param payload: The JSON payload to send in the request body.
+        :return: The parsed JSON response data.
+        :raises ClientError: For 4xx HTTP errors.
+        :raises ServerError: For 5xx HTTP errors.
+        """
         payload = payload or {}
         url = self.base_url + url_path
-        response = self.session.post(url, json=payload, timeout=self.timeout)
-        self._handle_exception(response)
+        
         try:
+            response = self.session.post(url, json=payload, timeout=self.timeout)
+            
+            # Raise exceptions for bad status codes (4xx and 5xx) immediately.
+            self._handle_exception(response)
+            
+            # Attempt to parse the JSON response for successful requests.
             return response.json()
-        except ValueError:
-            return {"error": f"Could not parse JSON: {response.text}"}
+            
+        except JSONDecodeError as e:
+            # Handle cases where the server returns a successful status (2xx) but non-JSON content.
+            self._logger.error(f"Failed to parse JSON response from {url}: {response.text}")
+            # Returning a structured error instead of just a raw dictionary for consistency.
+            raise ClientError(
+                response.status_code, 
+                code="JSON_PARSE_ERROR", 
+                msg=f"Could not parse JSON: {e}", 
+                data=response.text, 
+                headers=response.headers
+            )
+        except RequestException as e:
+            # Handle network/connection issues (e.g., DNS failure, timeout).
+            self._logger.error(f"Request failed for {url}: {e}")
+            raise ClientError(
+                503, 
+                code="NETWORK_ERROR", 
+                msg=f"Request failed due to network issue: {e}", 
+                data=None, 
+                headers=None
+            )
 
-    def _handle_exception(self, response):
+    def _handle_exception(self, response: requests.Response):
+        """
+        Handles HTTP status codes >= 400 by raising appropriate exceptions.
+        :param response: The requests.Response object.
+        :raises ClientError: For 4xx errors.
+        :raises ServerError: For 5xx errors.
+        """
         status_code = response.status_code
+        
         if status_code < 400:
             return
+
         if 400 <= status_code < 500:
+            # Handle 4xx Client Errors
             try:
-                err = json.loads(response.text)
+                # Attempt to parse the structured error response from the server.
+                err = response.json()
             except JSONDecodeError:
-                raise ClientError(status_code, None, response.text, None, response.headers)
-            if err is None:
-                raise ClientError(status_code, None, response.text, None, response.headers)
+                # If 4xx error is received but the body is not parsable JSON.
+                raise ClientError(status_code, code="UNSPECIFIED_4XX", msg=response.text, data=None, headers=response.headers)
+            
+            # Ensure the parsed error object is not None or empty if response.json() didn't fail.
+            if not err or not isinstance(err, dict):
+                 raise ClientError(status_code, code="INVALID_ERROR_FORMAT", msg=response.text, data=None, headers=response.headers)
+
+            # Raise the structured ClientError with details from the API response.
             error_data = err.get("data")
-            raise ClientError(status_code, err["code"], err["msg"], response.headers, error_data)
+            # Using keyword arguments for clarity, assuming the correct ClientError signature.
+            raise ClientError(
+                status_code, 
+                code=err.get("code"), 
+                msg=err.get("msg") or "Client error occurred.", 
+                data=error_data, 
+                headers=response.headers
+            )
+        
+        # Handle 5xx Server Errors
         raise ServerError(status_code, response.text)