diff --git a/nanobot/agent/loop.py b/nanobot/agent/loop.py
index 4a96b84..bfe6e89 100644
--- a/nanobot/agent/loop.py
+++ b/nanobot/agent/loop.py
@@ -40,14 +40,17 @@ class AgentLoop:
         workspace: Path,
         model: str | None = None,
         max_iterations: int = 20,
-        brave_api_key: str | None = None
+        brave_api_key: str | None = None,
+        exec_config: "ExecToolConfig | None" = None,
     ):
+        from nanobot.config.schema import ExecToolConfig
         self.bus = bus
         self.provider = provider
         self.workspace = workspace
         self.model = model or provider.get_default_model()
         self.max_iterations = max_iterations
         self.brave_api_key = brave_api_key
+        self.exec_config = exec_config or ExecToolConfig()
         
         self.context = ContextBuilder(workspace)
         self.sessions = SessionManager(workspace)
@@ -58,6 +61,7 @@ class AgentLoop:
             bus=bus,
             model=self.model,
             brave_api_key=brave_api_key,
+            exec_config=self.exec_config,
         )
         
         self._running = False
@@ -72,7 +76,11 @@ class AgentLoop:
         self.tools.register(ListDirTool())
         
         # Shell tool
-        self.tools.register(ExecTool(working_dir=str(self.workspace)))
+        self.tools.register(ExecTool(
+            working_dir=str(self.workspace),
+            timeout=self.exec_config.timeout,
+            restrict_to_workspace=self.exec_config.restrict_to_workspace,
+        ))
         
         # Web tools
         self.tools.register(WebSearchTool(api_key=self.brave_api_key))
diff --git a/nanobot/agent/subagent.py b/nanobot/agent/subagent.py
index d3b320c..05ffbb8 100644
--- a/nanobot/agent/subagent.py
+++ b/nanobot/agent/subagent.py
@@ -33,12 +33,15 @@ class SubagentManager:
         bus: MessageBus,
         model: str | None = None,
         brave_api_key: str | None = None,
+        exec_config: "ExecToolConfig | None" = None,
     ):
+        from nanobot.config.schema import ExecToolConfig
         self.provider = provider
         self.workspace = workspace
         self.bus = bus
         self.model = model or provider.get_default_model()
         self.brave_api_key = brave_api_key
+        self.exec_config = exec_config or ExecToolConfig()
         self._running_tasks: dict[str, asyncio.Task[None]] = {}
     
     async def spawn(
@@ -96,7 +99,11 @@ class SubagentManager:
             tools.register(ReadFileTool())
             tools.register(WriteFileTool())
             tools.register(ListDirTool())
-            tools.register(ExecTool(working_dir=str(self.workspace)))
+            tools.register(ExecTool(
+                working_dir=str(self.workspace),
+                timeout=self.exec_config.timeout,
+                restrict_to_workspace=self.exec_config.restrict_to_workspace,
+            ))
             tools.register(WebSearchTool(api_key=self.brave_api_key))
             tools.register(WebFetchTool())
             
diff --git a/nanobot/agent/tools/base.py b/nanobot/agent/tools/base.py
index 6fcfec6..cbaadbd 100644
--- a/nanobot/agent/tools/base.py
+++ b/nanobot/agent/tools/base.py
@@ -12,6 +12,15 @@ class Tool(ABC):
     the environment, such as reading files, executing commands, etc.
     """
     
+    _TYPE_MAP = {
+        "string": str,
+        "integer": int,
+        "number": (int, float),
+        "boolean": bool,
+        "array": list,
+        "object": dict,
+    }
+    
     @property
     @abstractmethod
     def name(self) -> str:
@@ -42,6 +51,65 @@ class Tool(ABC):
             String result of the tool execution.
         """
         pass
+
+    def validate_params(self, params: dict[str, Any]) -> list[str]:
+        """
+        Lightweight JSON schema validation for tool parameters.
+
+        Returns a list of error strings (empty if valid).
+        Unknown params are ignored.
+        """
+        schema = self.parameters or {}
+
+        # Default to an object schema if type is missing, and fail fast on unsupported top-level types.
+        if "type" not in schema:
+            schema = {"type": "object", **schema}
+        elif schema.get("type") != "object":
+            raise ValueError(
+                f"Tool parameter schemas must have top-level type 'object'; got {schema.get('type')!r}"
+            )
+
+        return self._validate_schema(params, schema, path="")
+
+    def _validate_schema(self, value: Any, schema: dict[str, Any], path: str) -> list[str]:
+        errors: list[str] = []
+        expected_type = schema.get("type")
+        label = path or "parameter"
+
+        if expected_type in self._TYPE_MAP and not isinstance(value, self._TYPE_MAP[expected_type]):
+            return [f"{label} should be {expected_type}"]
+
+        if "enum" in schema and value not in schema["enum"]:
+            errors.append(f"{label} must be one of {schema['enum']}")
+
+        if expected_type in ("integer", "number"):
+            if "minimum" in schema and value < schema["minimum"]:
+                errors.append(f"{label} must be >= {schema['minimum']}")
+            if "maximum" in schema and value > schema["maximum"]:
+                errors.append(f"{label} must be <= {schema['maximum']}")
+
+        if expected_type == "string":
+            if "minLength" in schema and len(value) < schema["minLength"]:
+                errors.append(f"{label} must be at least {schema['minLength']} chars")
+            if "maxLength" in schema and len(value) > schema["maxLength"]:
+                errors.append(f"{label} must be at most {schema['maxLength']} chars")
+
+        if expected_type == "object":
+            properties = schema.get("properties", {})
+            for key in schema.get("required", []):
+                if key not in value:
+                    errors.append(f"missing required {path}.{key}" if path else f"missing required {key}")
+            for key, item in value.items():
+                if key in properties:
+                    errors.extend(self._validate_schema(item, properties[key], f"{path}.{key}" if path else key))
+
+        if expected_type == "array":
+            items_schema = schema.get("items")
+            if items_schema:
+                for idx, item in enumerate(value):
+                    errors.extend(self._validate_schema(item, items_schema, f"{path}[{idx}]" if path else f"[{idx}]"))
+
+        return errors
     
     def to_schema(self) -> dict[str, Any]:
         """Convert tool to OpenAI function schema format."""
diff --git a/nanobot/agent/tools/registry.py b/nanobot/agent/tools/registry.py
index 1e8f56d..d9b33ff 100644
--- a/nanobot/agent/tools/registry.py
+++ b/nanobot/agent/tools/registry.py
@@ -52,8 +52,11 @@ class ToolRegistry:
         tool = self._tools.get(name)
         if not tool:
             return f"Error: Tool '{name}' not found"
-        
+
         try:
+            errors = tool.validate_params(params)
+            if errors:
+                return f"Error: Invalid parameters for tool '{name}': " + "; ".join(errors)
             return await tool.execute(**params)
         except Exception as e:
             return f"Error executing {name}: {str(e)}"
diff --git a/nanobot/agent/tools/shell.py b/nanobot/agent/tools/shell.py
index bf7f064..143d187 100644
--- a/nanobot/agent/tools/shell.py
+++ b/nanobot/agent/tools/shell.py
@@ -2,6 +2,8 @@
 
 import asyncio
 import os
+import re
+from pathlib import Path
 from typing import Any
 
 from nanobot.agent.tools.base import Tool
@@ -10,9 +12,28 @@ from nanobot.agent.tools.base import Tool
 class ExecTool(Tool):
     """Tool to execute shell commands."""
     
-    def __init__(self, timeout: int = 60, working_dir: str | None = None):
+    def __init__(
+        self,
+        timeout: int = 60,
+        working_dir: str | None = None,
+        deny_patterns: list[str] | None = None,
+        allow_patterns: list[str] | None = None,
+        restrict_to_workspace: bool = False,
+    ):
         self.timeout = timeout
         self.working_dir = working_dir
+        self.deny_patterns = deny_patterns or [
+            r"\brm\s+-[rf]{1,2}\b",          # rm -r, rm -rf, rm -fr
+            r"\bdel\s+/[fq]\b",              # del /f, del /q
+            r"\brmdir\s+/s\b",               # rmdir /s
+            r"\b(format|mkfs|diskpart)\b",   # disk operations
+            r"\bdd\s+if=",                   # dd
+            r">\s*/dev/sd",                  # write to disk
+            r"\b(shutdown|reboot|poweroff)\b",  # system power
+            r":\(\)\s*\{.*\};\s*:",          # fork bomb
+        ]
+        self.allow_patterns = allow_patterns or []
+        self.restrict_to_workspace = restrict_to_workspace
     
     @property
     def name(self) -> str:
@@ -41,6 +62,9 @@ class ExecTool(Tool):
     
     async def execute(self, command: str, working_dir: str | None = None, **kwargs: Any) -> str:
         cwd = working_dir or self.working_dir or os.getcwd()
+        guard_error = self._guard_command(command, cwd)
+        if guard_error:
+            return guard_error
         
         try:
             process = await asyncio.create_subprocess_shell(
@@ -83,3 +107,35 @@ class ExecTool(Tool):
             
         except Exception as e:
             return f"Error executing command: {str(e)}"
+
+    def _guard_command(self, command: str, cwd: str) -> str | None:
+        """Best-effort safety guard for potentially destructive commands."""
+        cmd = command.strip()
+        lower = cmd.lower()
+
+        for pattern in self.deny_patterns:
+            if re.search(pattern, lower):
+                return "Error: Command blocked by safety guard (dangerous pattern detected)"
+
+        if self.allow_patterns:
+            if not any(re.search(p, lower) for p in self.allow_patterns):
+                return "Error: Command blocked by safety guard (not in allowlist)"
+
+        if self.restrict_to_workspace:
+            if "..\\" in cmd or "../" in cmd:
+                return "Error: Command blocked by safety guard (path traversal detected)"
+
+            cwd_path = Path(cwd).resolve()
+
+            win_paths = re.findall(r"[A-Za-z]:\\[^\\\"']+", cmd)
+            posix_paths = re.findall(r"/[^\s\"']+", cmd)
+
+            for raw in win_paths + posix_paths:
+                try:
+                    p = Path(raw).resolve()
+                except Exception:
+                    continue
+                if cwd_path not in p.parents and p != cwd_path:
+                    return "Error: Command blocked by safety guard (path outside working dir)"
+
+        return None
diff --git a/nanobot/cli/commands.py b/nanobot/cli/commands.py
index 5ecc31b..6b95667 100644
--- a/nanobot/cli/commands.py
+++ b/nanobot/cli/commands.py
@@ -202,7 +202,8 @@ def gateway(
         workspace=config.workspace_path,
         model=config.agents.defaults.model,
         max_iterations=config.agents.defaults.max_tool_iterations,
-        brave_api_key=config.tools.web.search.api_key or None
+        brave_api_key=config.tools.web.search.api_key or None,
+        exec_config=config.tools.exec,
     )
     
     # Create cron service
@@ -309,7 +310,8 @@ def agent(
         bus=bus,
         provider=provider,
         workspace=config.workspace_path,
-        brave_api_key=config.tools.web.search.api_key or None
+        brave_api_key=config.tools.web.search.api_key or None,
+        exec_config=config.tools.exec,
     )
     
     if message:
diff --git a/nanobot/config/schema.py b/nanobot/config/schema.py
index 71e3361..4c34834 100644
--- a/nanobot/config/schema.py
+++ b/nanobot/config/schema.py
@@ -73,9 +73,16 @@ class WebToolsConfig(BaseModel):
     search: WebSearchConfig = Field(default_factory=WebSearchConfig)
 
 
+class ExecToolConfig(BaseModel):
+    """Shell exec tool configuration."""
+    timeout: int = 60
+    restrict_to_workspace: bool = False  # If true, block commands accessing paths outside workspace
+
+
 class ToolsConfig(BaseModel):
     """Tools configuration."""
     web: WebToolsConfig = Field(default_factory=WebToolsConfig)
+    exec: ExecToolConfig = Field(default_factory=ExecToolConfig)
 
 
 class Config(BaseSettings):
diff --git a/tests/test_tool_validation.py b/tests/test_tool_validation.py
new file mode 100644
index 0000000..f11c667
--- /dev/null
+++ b/tests/test_tool_validation.py
@@ -0,0 +1,88 @@
+from typing import Any
+
+from nanobot.agent.tools.base import Tool
+from nanobot.agent.tools.registry import ToolRegistry
+
+
+class SampleTool(Tool):
+    @property
+    def name(self) -> str:
+        return "sample"
+
+    @property
+    def description(self) -> str:
+        return "sample tool"
+
+    @property
+    def parameters(self) -> dict[str, Any]:
+        return {
+            "type": "object",
+            "properties": {
+                "query": {"type": "string", "minLength": 2},
+                "count": {"type": "integer", "minimum": 1, "maximum": 10},
+                "mode": {"type": "string", "enum": ["fast", "full"]},
+                "meta": {
+                    "type": "object",
+                    "properties": {
+                        "tag": {"type": "string"},
+                        "flags": {
+                            "type": "array",
+                            "items": {"type": "string"},
+                        },
+                    },
+                    "required": ["tag"],
+                },
+            },
+            "required": ["query", "count"],
+        }
+
+    async def execute(self, **kwargs: Any) -> str:
+        return "ok"
+
+
+def test_validate_params_missing_required() -> None:
+    tool = SampleTool()
+    errors = tool.validate_params({"query": "hi"})
+    assert "missing required count" in "; ".join(errors)
+
+
+def test_validate_params_type_and_range() -> None:
+    tool = SampleTool()
+    errors = tool.validate_params({"query": "hi", "count": 0})
+    assert any("count must be >= 1" in e for e in errors)
+
+    errors = tool.validate_params({"query": "hi", "count": "2"})
+    assert any("count should be integer" in e for e in errors)
+
+
+def test_validate_params_enum_and_min_length() -> None:
+    tool = SampleTool()
+    errors = tool.validate_params({"query": "h", "count": 2, "mode": "slow"})
+    assert any("query must be at least 2 chars" in e for e in errors)
+    assert any("mode must be one of" in e for e in errors)
+
+
+def test_validate_params_nested_object_and_array() -> None:
+    tool = SampleTool()
+    errors = tool.validate_params(
+        {
+            "query": "hi",
+            "count": 2,
+            "meta": {"flags": [1, "ok"]},
+        }
+    )
+    assert any("missing required meta.tag" in e for e in errors)
+    assert any("meta.flags[0] should be string" in e for e in errors)
+
+
+def test_validate_params_ignores_unknown_fields() -> None:
+    tool = SampleTool()
+    errors = tool.validate_params({"query": "hi", "count": 2, "extra": "x"})
+    assert errors == []
+
+
+async def test_registry_returns_validation_error() -> None:
+    reg = ToolRegistry()
+    reg.register(SampleTool())
+    result = await reg.execute("sample", {"query": "hi"})
+    assert "Invalid parameters" in result