diff --git a/agentflow_cli/src/app/core/middleware/request_limits.py b/agentflow_cli/src/app/core/middleware/request_limits.py
index b5f0826..b2a833d 100644
--- a/agentflow_cli/src/app/core/middleware/request_limits.py
+++ b/agentflow_cli/src/app/core/middleware/request_limits.py
@@ -56,8 +56,7 @@ async def dispatch(self, request: Request, call_next):
                         "error": {
                             "code": "REQUEST_TOO_LARGE",
                             "message": (
-                                f"Request body too large. "
-                                f"Maximum size is {self.max_size_mb:.1f}MB"
+                                f"Request body too large. Maximum size is {self.max_size_mb:.1f}MB"
                             ),
                             "max_size_bytes": self.max_size,
                             "max_size_mb": self.max_size_mb,
diff --git a/agentflow_cli/src/app/loader.py b/agentflow_cli/src/app/loader.py
index 3692c3d..1fbfdb7 100644
--- a/agentflow_cli/src/app/loader.py
+++ b/agentflow_cli/src/app/loader.py
@@ -22,6 +22,9 @@
 
 
 async def load_graph(path: str) -> CompiledGraph | None:
+    if ":" not in path:
+        raise ValueError(f"Invalid graph path format '{path}'. Expected 'module:attribute'.")
+
     module_name_importable, function_name = path.split(":")
 
     try:
@@ -44,6 +47,12 @@ async def load_graph(path: str) -> CompiledGraph | None:
         else:
             raise TypeError("Loaded object is not a CompiledGraph.")
 
+    except ModuleNotFoundError as e:
+        logger.error(f"Module not found when loading graph from {path}: {e}")
+        raise ModuleNotFoundError(f"Module not found for graph path '{path}': {e}")
+    except AttributeError as e:
+        logger.error(f"Attribute not found when loading graph from {path}: {e}")
+        raise AttributeError(f"Attribute not found for graph path '{path}': {e}")
     except Exception as e:
         logger.error(f"Error loading graph from {path}: {e}")
         raise Exception(f"Failed to load graph from {path}: {e}")
@@ -55,6 +64,9 @@ def load_checkpointer(path: str | None) -> BaseCheckpointer | None:
     if not path:
         return None
 
+    if ":" not in path:
+        raise ValueError(f"Invalid checkpointer path format '{path}'. Expected 'module:attribute'.")
+
     module_name_importable, function_name = path.split(":")
 
     try:
@@ -69,6 +81,12 @@ def load_checkpointer(path: str | None) -> BaseCheckpointer | None:
             logger.info(f"Successfully loaded BaseCheckpointer '{function_name}' from {path}.")
         else:
             raise TypeError("Loaded object is not a BaseCheckpointer.")
+    except ModuleNotFoundError as e:
+        logger.error(f"Module not found when loading BaseCheckpointer from {path}: {e}")
+        raise ModuleNotFoundError(f"Module not found for checkpointer path '{path}': {e}")
+    except AttributeError as e:
+        logger.error(f"Attribute not found when loading BaseCheckpointer from {path}: {e}")
+        raise AttributeError(f"Attribute not found for checkpointer path '{path}': {e}")
     except Exception as e:
         logger.error(f"Error loading BaseCheckpointer from {path}: {e}")
         raise Exception(f"Failed to load BaseCheckpointer from {path}: {e}")
@@ -80,6 +98,9 @@ def load_store(path: str | None) -> BaseStore | None:
     if not path:
         return None
 
+    if ":" not in path:
+        raise ValueError(f"Invalid store path format '{path}'. Expected 'module:attribute'.")
+
     module_name_importable, function_name = path.split(":")
 
     try:
@@ -94,6 +115,12 @@ def load_store(path: str | None) -> BaseStore | None:
             logger.info(f"Successfully loaded graph '{function_name}' from {path}.")
         else:
             raise TypeError("Loaded object is not a BaseStore.")
+    except ModuleNotFoundError as e:
+        logger.error(f"Module not found when loading BaseStore from {path}: {e}")
+        raise ModuleNotFoundError(f"Module not found for store path '{path}': {e}")
+    except AttributeError as e:
+        logger.error(f"Attribute not found when loading BaseStore from {path}: {e}")
+        raise AttributeError(f"Attribute not found for store path '{path}': {e}")
     except Exception as e:
         logger.error(f"Error loading BaseStore from {path}: {e}")
         raise Exception(f"Failed to load BaseStore from {path}: {e}")
@@ -134,13 +161,15 @@ def load_auth(path: str | None) -> BaseAuth | None:
     if not path:
         return None
 
+    if ":" not in path:
+        raise ValueError(f"Invalid auth path format '{path}'. Expected 'module:attribute'.")
+
     module_name_importable, function_name = path.split(":")
 
     try:
         module = importlib.import_module(module_name_importable)
         entry_point_obj = getattr(module, function_name)
 
-        # If it's a class, instantiate it; if it's an instance, use as is
         if inspect.isclass(entry_point_obj) and issubclass(entry_point_obj, BaseAuth):
             auth = entry_point_obj()
         elif isinstance(entry_point_obj, BaseAuth):
@@ -149,6 +178,12 @@ def load_auth(path: str | None) -> BaseAuth | None:
             raise TypeError("Loaded object is not a subclass or instance of BaseAuth.")
 
         logger.info(f"Successfully loaded BaseAuth '{function_name}' from {path}.")
+    except ModuleNotFoundError as e:
+        logger.error(f"Module not found when loading BaseAuth from {path}: {e}")
+        raise ModuleNotFoundError(f"Module not found for auth path '{path}': {e}")
+    except AttributeError as e:
+        logger.error(f"Attribute not found when loading BaseAuth from {path}: {e}")
+        raise AttributeError(f"Attribute not found for auth path '{path}': {e}")
     except Exception as e:
         logger.error(f"Error loading BaseAuth from {path}: {e}")
         raise Exception(f"Failed to load BaseAuth from {path}: {e}")
diff --git a/agentflow_cli/src/app/routers/checkpointer/router.py b/agentflow_cli/src/app/routers/checkpointer/router.py
index 9a1653e..152562e 100644
--- a/agentflow_cli/src/app/routers/checkpointer/router.py
+++ b/agentflow_cli/src/app/routers/checkpointer/router.py
@@ -3,7 +3,7 @@
 from typing import Any
 
 from agentflow.state import Message
-from fastapi import APIRouter, Depends, Request, status
+from fastapi import APIRouter, Depends, HTTPException, Request, status
 from injectq.integrations import InjectAPI
 
 from agentflow_cli.src.app.core.auth.permissions import RequirePermission
@@ -26,6 +26,26 @@
 router = APIRouter(tags=["checkpointer"])
 
 
+def validate_thread_id(thread_id: int | str) -> None:
+    if isinstance(thread_id, str):
+        if not thread_id.strip():
+            raise HTTPException(
+                status_code=422,
+                detail="thread_id cannot be empty or whitespace"
+            )
+    elif isinstance(thread_id, int):
+        if thread_id < 1:
+            raise HTTPException(
+                status_code=422,
+                detail="thread_id must be a non-negative integer"
+            )
+    else:
+        raise HTTPException(
+            status_code=422,
+            detail="thread_id must be a string or integer"
+        )
+
+
 @router.get(
     "/v1/threads/{thread_id}/state",
     status_code=status.HTTP_200_OK,
@@ -48,6 +68,8 @@ async def get_state(
     Returns:
         State response with state data or error
     """
+    validate_thread_id(thread_id)
+
     config = {"thread_id": thread_id}
 
     result = await service.get_state(
@@ -86,11 +108,11 @@ async def put_state(
     Returns:
         Success response or error
     """
+    validate_thread_id(thread_id)
     config = {"thread_id": thread_id}
     if payload.config:
         config.update(payload.config)
 
-    # State is provided as dict; service will handle merging/reconstruction
     res = await service.put_state(
         config,
         user,
@@ -127,6 +149,7 @@ async def clear_state(
     Returns:
         Success response or error
     """
+    validate_thread_id(thread_id)
     config = {"thread_id": thread_id}
 
     res = await service.clear_state(
@@ -168,7 +191,10 @@ async def put_messages(
     Returns:
         Success response or error
     """
-    # Convert message dicts to Message objects if needed
+    validate_thread_id(thread_id)
+    if not payload.messages:
+        raise HTTPException(status_code=422, detail="messages must not be empty")
+
     config = {"thread_id": thread_id}
     if payload.config:
         config.update(payload.config)
@@ -213,6 +239,10 @@ async def get_message(
     Returns:
         Message response with message data or error
     """
+    validate_thread_id(thread_id)
+    if not message_id or (isinstance(message_id, str) and not str(message_id).strip()):
+        raise HTTPException(status_code=422, detail="message_id is required and cannot be empty")
+
     config = {"thread_id": thread_id}
 
     result = await service.get_message(
@@ -255,6 +285,12 @@ async def list_messages(
     Returns:
         Messages list response with messages data or error
     """
+    validate_thread_id(thread_id)
+    if offset is not None and offset < 0:
+        raise HTTPException(status_code=422, detail="offset must be >= 0")
+    if limit is not None and limit <= 0:
+        raise HTTPException(status_code=422, detail="limit must be > 0")
+
     config = {"thread_id": thread_id}
 
     result = await service.get_messages(
@@ -297,6 +333,10 @@ async def delete_message(
     Returns:
         Success response or error
     """
+    validate_thread_id(thread_id)
+    if not message_id or (isinstance(message_id, str) and not str(message_id).strip()):
+        raise HTTPException(status_code=422, detail="message_id is required and cannot be empty")
+
     config = {"thread_id": thread_id}
     if payload.config:
         config.update(payload.config)
@@ -340,6 +380,7 @@ async def get_thread(
     Returns:
         Thread response with thread data or error
     """
+    validate_thread_id(thread_id)
     result = await service.get_thread(
         {"thread_id": thread_id},
         user,
@@ -415,6 +456,7 @@ async def delete_thread(
     Returns:
         Success response or error
     """
+    validate_thread_id(thread_id)
     config = {"thread_id": thread_id}
     if payload.config:
         config.update(payload.config)
diff --git a/agentflow_cli/src/app/routers/checkpointer/services/checkpointer_service.py b/agentflow_cli/src/app/routers/checkpointer/services/checkpointer_service.py
index ce9ef14..03c374f 100644
--- a/agentflow_cli/src/app/routers/checkpointer/services/checkpointer_service.py
+++ b/agentflow_cli/src/app/routers/checkpointer/services/checkpointer_service.py
@@ -2,6 +2,7 @@
 
 from agentflow.checkpointer import BaseCheckpointer
 from agentflow.state import AgentState, Message
+from fastapi import HTTPException
 from injectq import inject, singleton
 
 from agentflow_cli.src.app.core import logger
@@ -26,7 +27,7 @@ def __init__(self, checkpointer: BaseCheckpointer):
 
     def _config(self, config: dict[str, Any] | None, user: dict) -> dict[str, Any]:
         if not self.checkpointer:
-            raise ValueError("Checkpointer is not configured")
+            raise HTTPException(status_code=503, detail="Checkpointer service is not available")
 
         cfg: dict[str, Any] = dict(config or {})
         cfg["user"] = user
diff --git a/agentflow_cli/src/app/routers/graph/schemas/graph_schemas.py b/agentflow_cli/src/app/routers/graph/schemas/graph_schemas.py
index 1d994f8..2f07170 100644
--- a/agentflow_cli/src/app/routers/graph/schemas/graph_schemas.py
+++ b/agentflow_cli/src/app/routers/graph/schemas/graph_schemas.py
@@ -2,7 +2,7 @@
 
 from agentflow.state import Message
 from agentflow.utils import ResponseGranularity
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, field_validator
 
 
 class GraphInputSchema(BaseModel):
@@ -23,8 +23,18 @@ class GraphInputSchema(BaseModel):
     )
     recursion_limit: int = Field(
         default=25,
+        ge=1,
+        le=100,
         description="Maximum recursion limit for graph execution",
     )
+
+    @field_validator("messages")
+    @classmethod
+    def messages_must_not_be_empty(cls, v: list[Message]) -> list[Message]:
+        if not v:
+            raise ValueError("messages must contain at least one message")
+        return v
+
     response_granularity: ResponseGranularity = Field(
         default=ResponseGranularity.LOW,
         description="Granularity of the response (full, partial, low)",
@@ -111,7 +121,15 @@ class GraphSchema(BaseModel):
 class GraphStopSchema(BaseModel):
     """Schema for stopping graph execution."""
 
-    thread_id: str = Field(..., description="Thread ID to stop execution for")
+    thread_id: str = Field(..., min_length=1, description="Thread ID to stop execution for")
+
+    @field_validator("thread_id")
+    @classmethod
+    def thread_id_not_blank(cls, v: str) -> str:
+        if not v.strip():
+            raise ValueError("thread_id cannot be empty or whitespace")
+        return v.strip()
+
     config: dict[str, Any] | None = Field(
         default=None, description="Optional configuration for the stop operation"
     )
@@ -137,7 +155,15 @@ class GraphSetupSchema(BaseModel):
 class FixGraphRequestSchema(BaseModel):
     """Schema for fixing graph state by removing messages with empty tool call content."""
 
-    thread_id: str = Field(..., description="Thread ID to fix the graph state for")
+    thread_id: str = Field(..., min_length=1, description="Thread ID to fix the graph state for")
+
+    @field_validator("thread_id")
+    @classmethod
+    def thread_id_not_blank(cls, v: str) -> str:
+        if not v.strip():
+            raise ValueError("thread_id cannot be empty or whitespace")
+        return v.strip()
+
     config: dict[str, Any] | None = Field(
         default=None, description="Optional configuration for the fix operation"
     )
diff --git a/agentflow_cli/src/app/routers/graph/services/graph_service.py b/agentflow_cli/src/app/routers/graph/services/graph_service.py
index c357e4d..3786d38 100644
--- a/agentflow_cli/src/app/routers/graph/services/graph_service.py
+++ b/agentflow_cli/src/app/routers/graph/services/graph_service.py
@@ -154,6 +154,9 @@ async def stop_graph(
             logger.info(f"Graph stop completed for thread {thread_id}: {result}")
             return result
 
+        except ValueError as e:
+            logger.warning(f"Graph stop input validation failed for thread {thread_id}: {e}")
+            raise HTTPException(status_code=422, detail=str(e))
         except Exception as e:
             logger.error(f"Graph stop failed for thread {thread_id}: {e}")
             raise HTTPException(
@@ -166,8 +169,8 @@ async def _prepare_input(
     ):
         is_new_thread = False
         config = graph_input.config or {}
-        if "thread_id" in config:
-            thread_id = config["thread_id"]
+        if config.get("thread_id") and str(config["thread_id"]).strip():
+            thread_id = str(config["thread_id"]).strip()
         else:
             thread_id = await InjectQ.get_instance().atry_get("generated_id") or str(uuid4())
             is_new_thread = True
@@ -258,6 +261,9 @@ async def invoke_graph(
                 meta=meta,
             )
 
+        except ValueError as e:
+            logger.warning(f"Graph input validation failed: {e}")
+            raise HTTPException(status_code=422, detail=str(e))
         except Exception as e:
             logger.error(f"Graph execution failed: {e}")
             raise HTTPException(status_code=500, detail=f"Graph execution failed: {e!s}")
@@ -334,6 +340,9 @@ async def stream_graph(
                     + "\n"
                 )
 
+        except ValueError as e:
+            logger.warning(f"Graph stream input validation failed: {e}")
+            raise HTTPException(status_code=422, detail=str(e))
         except Exception as e:
             logger.error(f"Graph streaming failed: {e}")
             raise HTTPException(status_code=500, detail=f"Graph streaming failed: {e!s}")
@@ -341,9 +350,11 @@ async def stream_graph(
     async def graph_details(self) -> GraphSchema:
         try:
             logger.info("Getting graph details")
-            # Fetch and return graph details
             res = self._graph.generate_graph()
             return GraphSchema(**res)
+        except ValueError as e:
+            logger.warning(f"Graph details validation failed: {e}")
+            raise HTTPException(status_code=422, detail=str(e))
         except Exception as e:
             logger.error(f"Failed to get graph details: {e}")
             raise HTTPException(status_code=500, detail=f"Failed to get graph details: {e!s}")
@@ -351,9 +362,11 @@ async def graph_details(self) -> GraphSchema:
     async def get_state_schema(self) -> dict:
         try:
             logger.info("Getting state schema")
-            # Fetch and return state schema
             res: BaseModel = self._graph._state
             return res.model_json_schema()
+        except ValueError as e:
+            logger.warning(f"State schema validation failed: {e}")
+            raise HTTPException(status_code=422, detail=str(e))
         except Exception as e:
             logger.error(f"Failed to get state schema: {e}")
             raise HTTPException(status_code=500, detail=f"Failed to get state schema: {e!s}")
@@ -451,6 +464,9 @@ async def fix_graph(
                 "removed_count": removed_count,
                 "state": state.model_dump_json(serialize_as_any=True),
             }
+        except ValueError as e:
+            logger.warning(f"Fix graph input validation failed: {e}")
+            raise HTTPException(status_code=422, detail=str(e))
         except Exception as e:
             logger.error(f"Fix graph operation failed: {e}")
             raise HTTPException(status_code=500, detail=f"Fix graph operation failed: {e!s}")
diff --git a/agentflow_cli/src/app/routers/store/router.py b/agentflow_cli/src/app/routers/store/router.py
index 8c2f047..2bf3522 100644
--- a/agentflow_cli/src/app/routers/store/router.py
+++ b/agentflow_cli/src/app/routers/store/router.py
@@ -4,7 +4,7 @@
 
 from typing import Any
 
-from fastapi import APIRouter, Body, Depends, Request, status
+from fastapi import APIRouter, Body, Depends, HTTPException, Request, status
 from injectq.integrations import InjectAPI
 
 from agentflow_cli.src.app.core.auth.permissions import RequirePermission
@@ -64,6 +64,8 @@ async def search_memories(
     user: dict[str, Any] = Depends(RequirePermission("store", "read")),
 ):
     """Search stored memories."""
+    if not payload.query or (isinstance(payload.query, str) and not payload.query.strip()):
+        raise HTTPException(status_code=422, detail="query is required and cannot be empty")
 
     result = await service.search_memories(payload, user)
     return success_response(result, request)
@@ -87,6 +89,8 @@ async def get_memory(
     user: dict[str, Any] = Depends(RequirePermission("store", "read")),
 ):
     """Get a memory by ID."""
+    if not memory_id or not memory_id.strip():
+        raise HTTPException(status_code=422, detail="memory_id is required and cannot be empty")
 
     cfg = payload.config if payload else {}
     opts = payload.options if payload else None
@@ -112,6 +116,9 @@ async def list_memories(
 ):
     """List stored memories."""
 
+    if payload and payload.limit is not None and payload.limit <= 0:
+        raise HTTPException(status_code=422, detail="limit must be > 0")
+
     if payload is None:
         payload = ListMemoriesSchema()
     cfg = payload.config or {}
@@ -135,6 +142,8 @@ async def update_memory(
     user: dict[str, Any] = Depends(RequirePermission("store", "write")),
 ):
     """Update a stored memory."""
+    if not memory_id or not memory_id.strip():
+        raise HTTPException(status_code=422, detail="memory_id is required and cannot be empty")
 
     result = await service.update_memory(memory_id, payload, user)
     return success_response(result, request, message="Memory updated successfully")
@@ -158,6 +167,8 @@ async def delete_memory(
     user: dict[str, Any] = Depends(RequirePermission("store", "delete")),
 ):
     """Delete a stored memory."""
+    if not memory_id or not memory_id.strip():
+        raise HTTPException(status_code=422, detail="memory_id is required and cannot be empty")
 
     config_payload = payload.config if payload else {}
     options_payload = payload.options if payload else None
diff --git a/agentflow_cli/src/app/routers/store/services/store_service.py b/agentflow_cli/src/app/routers/store/services/store_service.py
index d542894..c8df152 100644
--- a/agentflow_cli/src/app/routers/store/services/store_service.py
+++ b/agentflow_cli/src/app/routers/store/services/store_service.py
@@ -4,6 +4,7 @@
 
 from agentflow.state import Message
 from agentflow.store import BaseStore
+from fastapi import HTTPException
 from injectq import inject, singleton
 
 from agentflow_cli.src.app.core import logger
@@ -30,7 +31,7 @@ def __init__(self, store: BaseStore | None):
 
     def _get_store(self) -> BaseStore:
         if not self.store:
-            raise ValueError("Store is not configured")
+            raise HTTPException(status_code=503, detail="Store service is not available")
         return self.store
 
     def _config(self, config: dict[str, Any] | None, user: dict[str, Any]) -> dict[str, Any]: