diff --git a/nanobot/agent/loop.py b/nanobot/agent/loop.py
index 6a90349a0..b8a2745da 100644
--- a/nanobot/agent/loop.py
+++ b/nanobot/agent/loop.py
@@ -161,6 +161,7 @@ class AgentLoop:
         unified_session: bool = False,
         disabled_skills: list[str] | None = None,
         self_evolution: bool = False,
+        self_modify: bool = True,
     ):
         from nanobot.config.schema import ExecToolConfig, WebToolsConfig
 
@@ -248,7 +249,7 @@ class AgentLoop:
         )
         self._register_default_tools()
         if self_evolution:
-            self.tools.register(SelfTool(loop=self))
+            self.tools.register(SelfTool(loop=self, modify_allowed=self_modify))
         self._config_defaults: dict[str, Any] = {
             "max_iterations": self.max_iterations,
             "context_window_tokens": self.context_window_tokens,
diff --git a/nanobot/agent/tools/self.py b/nanobot/agent/tools/self.py
index 33ac097bc..c83e52ab9 100644
--- a/nanobot/agent/tools/self.py
+++ b/nanobot/agent/tools/self.py
@@ -60,8 +60,9 @@ class SelfTool(Tool):
     _MAX_RUNTIME_KEYS = 64
     _CALL_TIMEOUT_SECONDS = 30
 
-    def __init__(self, loop: AgentLoop) -> None:
+    def __init__(self, loop: AgentLoop, modify_allowed: bool = True) -> None:
         self._loop = loop
+        self._modify_allowed = modify_allowed
         self._channel = ""
         self._chat_id = ""
 
@@ -70,6 +71,7 @@ class SelfTool(Tool):
         result = cls.__new__(cls)
         memo[id(self)] = result
         result._loop = self._loop
+        result._modify_allowed = self._modify_allowed
         result._channel = self._channel
         result._chat_id = self._chat_id
         return result
@@ -84,18 +86,24 @@ class SelfTool(Tool):
 
     @property
     def description(self) -> str:
-        return (
+        base = (
             "Inspect and modify your own runtime state, navigate related objects, "
             "invoke methods, and save/restore configuration snapshots. "
             "Use 'inspect' with dot-path to explore (e.g. 'subagents._running_tasks'), "
             "'modify' to change values, 'call' to invoke methods, "
             "'list_tools' to see registered tools, 'manage_tool' to register/unregister, "
-            "'snapshot'/'restore' to save/load config templates.\n"
-            "IMPORTANT: Before modifying state or invoking methods, predict the potential impact. "
-            "If the operation could cause crashes, data loss, or instability "
-            "(e.g. replacing tools, changing model, resetting critical config), "
-            "warn the user about the risk BEFORE executing and ask for confirmation."
+            "'snapshot'/'restore' to save/load config templates."
         )
+        if not self._modify_allowed:
+            base += "\nREAD-ONLY MODE: modify, call, manage_tool, snapshot, restore, and reset are disabled."
+        else:
+            base += (
+                "\nIMPORTANT: Before modifying state or invoking methods, predict the potential impact. "
+                "If the operation could cause crashes, data loss, or instability "
+                "(e.g. replacing tools, changing model, resetting critical config), "
+                "warn the user about the risk BEFORE executing and ask for confirmation."
+            )
+        return base
 
     @property
     def parameters(self) -> dict[str, Any]:
@@ -297,20 +305,23 @@ class SelfTool(Tool):
     ) -> str:
         if action == "inspect":
             return self._inspect(key)
+        if action == "list_tools":
+            return self._list_tools()
+        if action == "list_snapshots":
+            return self._list_snapshots()
+        # Write operations — require modify_allowed
+        if not self._modify_allowed and action in ("modify", "call", "manage_tool", "reset", "snapshot", "restore"):
+            return "Error: modify actions are disabled (self_modify is False)"
         if action == "modify":
             return self._modify(key, value)
         if action == "call":
             return await self._call(method, args)
-        if action == "list_tools":
-            return self._list_tools()
         if action == "manage_tool":
             return self._manage_tool(manage_action, name)
         if action == "snapshot":
             return self._snapshot(name)
         if action == "restore":
             return self._restore(name)
-        if action == "list_snapshots":
-            return self._list_snapshots()
         if action == "reset":
             return self._reset(key)
         # Backward compat aliases
diff --git a/nanobot/cli/commands.py b/nanobot/cli/commands.py
index 0f9d451cb..f7337e2df 100644
--- a/nanobot/cli/commands.py
+++ b/nanobot/cli/commands.py
@@ -594,6 +594,7 @@ def serve(
         disabled_skills=runtime_config.agents.defaults.disabled_skills,
         session_ttl_minutes=runtime_config.agents.defaults.session_ttl_minutes,
         self_evolution=runtime_config.tools.self_evolution,
+        self_modify=runtime_config.tools.self_modify,
     )
 
     model_name = runtime_config.agents.defaults.model
@@ -689,6 +690,7 @@ def gateway(
         disabled_skills=config.agents.defaults.disabled_skills,
         session_ttl_minutes=config.agents.defaults.session_ttl_minutes,
         self_evolution=config.tools.self_evolution,
+        self_modify=config.tools.self_modify,
     )
 
     # Set cron callback (needs agent)
@@ -924,6 +926,7 @@ def agent(
         disabled_skills=config.agents.defaults.disabled_skills,
         session_ttl_minutes=config.agents.defaults.session_ttl_minutes,
         self_evolution=config.tools.self_evolution,
+        self_modify=config.tools.self_modify,
     )
     restart_notice = consume_restart_notice_from_env()
     if restart_notice and should_show_cli_restart_notice(restart_notice, session_id):
diff --git a/nanobot/config/schema.py b/nanobot/config/schema.py
index 45579d24c..a928aa20c 100644
--- a/nanobot/config/schema.py
+++ b/nanobot/config/schema.py
@@ -207,6 +207,7 @@ class ToolsConfig(Base):
     mcp_servers: dict[str, MCPServerConfig] = Field(default_factory=dict)
     ssrf_whitelist: list[str] = Field(default_factory=list)  # CIDR ranges to exempt from SSRF blocking (e.g. ["100.64.0.0/10"] for Tailscale)
     self_evolution: bool = False  # enable the self tool (agent can inspect/modify its own runtime state)
+    self_modify: bool = True  # allow self tool to modify state/call methods (read-only if False)
 
 
 class Config(BaseSettings):
diff --git a/nanobot/nanobot.py b/nanobot/nanobot.py
index 0b25f7f80..0521fb809 100644
--- a/nanobot/nanobot.py
+++ b/nanobot/nanobot.py
@@ -85,6 +85,7 @@ class Nanobot:
             disabled_skills=defaults.disabled_skills,
             session_ttl_minutes=defaults.session_ttl_minutes,
             self_evolution=config.tools.self_evolution,
+            self_modify=config.tools.self_modify,
         )
         return cls(loop)
 
diff --git a/tests/agent/tools/test_self_tool.py b/tests/agent/tools/test_self_tool.py
index 030ca3c99..fa619142d 100644
--- a/tests/agent/tools/test_self_tool.py
+++ b/tests/agent/tools/test_self_tool.py
@@ -1056,3 +1056,77 @@ class TestInspectTaskStatuses:
         assert "xyz" in result
         assert "search code" in result
         assert "stop_reason: completed" in result
+
+
+# ---------------------------------------------------------------------------
+# read-only mode (self_modify=False)
+# ---------------------------------------------------------------------------
+
+class TestReadOnlyMode:
+
+    def _make_readonly_tool(self):
+        loop = _make_mock_loop()
+        return SelfTool(loop=loop, modify_allowed=False)
+
+    @pytest.mark.asyncio
+    async def test_inspect_allowed_in_readonly(self):
+        tool = self._make_readonly_tool()
+        result = await tool.execute(action="inspect", key="max_iterations")
+        assert "40" in result
+
+    @pytest.mark.asyncio
+    async def test_list_tools_allowed_in_readonly(self):
+        tool = self._make_readonly_tool()
+        result = await tool.execute(action="list_tools")
+        assert "read_file" in result
+
+    @pytest.mark.asyncio
+    async def test_list_snapshots_allowed_in_readonly(self):
+        tool = self._make_readonly_tool()
+        result = await tool.execute(action="list_snapshots")
+        assert "No snapshots" in result
+
+    @pytest.mark.asyncio
+    async def test_modify_blocked_in_readonly(self):
+        tool = self._make_readonly_tool()
+        result = await tool.execute(action="modify", key="max_iterations", value=80)
+        assert "disabled" in result
+
+    @pytest.mark.asyncio
+    async def test_call_blocked_in_readonly(self):
+        tool = self._make_readonly_tool()
+        result = await tool.execute(action="call", method="subagents.get_running_count")
+        assert "disabled" in result
+
+    @pytest.mark.asyncio
+    async def test_manage_tool_blocked_in_readonly(self):
+        tool = self._make_readonly_tool()
+        result = await tool.execute(action="manage_tool", name="web_search", manage_action="unregister")
+        assert "disabled" in result
+
+    @pytest.mark.asyncio
+    async def test_snapshot_blocked_in_readonly(self):
+        tool = self._make_readonly_tool()
+        result = await tool.execute(action="snapshot", name="test")
+        assert "disabled" in result
+
+    @pytest.mark.asyncio
+    async def test_restore_blocked_in_readonly(self):
+        tool = self._make_readonly_tool()
+        result = await tool.execute(action="restore", name="test")
+        assert "disabled" in result
+
+    @pytest.mark.asyncio
+    async def test_reset_blocked_in_readonly(self):
+        tool = self._make_readonly_tool()
+        result = await tool.execute(action="reset", key="max_iterations")
+        assert "disabled" in result
+
+    def test_description_shows_readonly(self):
+        tool = self._make_readonly_tool()
+        assert "READ-ONLY MODE" in tool.description
+
+    def test_description_shows_warning_when_modify_allowed(self):
+        tool = _make_tool()
+        assert "IMPORTANT" in tool.description
+        assert "READ-ONLY" not in tool.description