diff --git a/src/google/adk/cli/api_server.py b/src/google/adk/cli/api_server.py
index 54708b28..1e4c504d 100644
--- a/src/google/adk/cli/api_server.py
+++ b/src/google/adk/cli/api_server.py
@@ -671,6 +671,15 @@ class ApiServer:
   instance returned by get_fast_api_app as this class exposes the agent runners
   and most other bits of state retained during the lifetime of the server.
 
+  Security:
+      The served endpoints are unauthenticated. Any client that can reach the
+      server can read and write sessions, memory, and artifacts and run agents
+      for any user or app. Run it only on a trusted network (for example bound
+      to localhost for local development) and do not expose it directly to
+      untrusted or public networks. Put it behind your own authentication and
+      authorization layer before serving multiple users or exposing it beyond
+      the local machine.
+
   Attributes:
       agent_loader: An instance of BaseAgentLoader for loading agents.
       session_service: An instance of BaseSessionService for managing sessions.
diff --git a/src/google/adk/cli/cli_tools_click.py b/src/google/adk/cli/cli_tools_click.py
index fd10057c..7a9b6647 100644
--- a/src/google/adk/cli/cli_tools_click.py
+++ b/src/google/adk/cli/cli_tools_click.py
@@ -1961,6 +1961,10 @@ def cli_web(
   agent containing `agent.py`, `__init__.py`, or `root_agent.yaml`) or a path
   pointing directly to a single agent folder.
 
+  This server is intended for local development. Its endpoints are
+  unauthenticated, so run it on a trusted network only and do not expose it to
+  untrusted or public networks.
+
   Example:
 
     adk web --session_service_uri=[uri] --port=[port] path/to/agents_dir
@@ -2102,6 +2106,10 @@ def cli_api_server(
   agent containing `agent.py`, `__init__.py`, or `root_agent.yaml`) or a path
   pointing directly to a single agent folder.
 
+  This server's endpoints are unauthenticated. Run it on a trusted network
+  only, and put it behind your own authentication and authorization layer
+  before exposing it to untrusted or public networks or serving multiple users.
+
   Example:
 
     adk api_server --session_service_uri=[uri] --port=[port] path/to/agents_dir
diff --git a/src/google/adk/cli/dev_server.py b/src/google/adk/cli/dev_server.py
index 2d01f60f..2237ecda 100644
--- a/src/google/adk/cli/dev_server.py
+++ b/src/google/adk/cli/dev_server.py
@@ -20,6 +20,12 @@ All dev-only endpoints (eval, debug, graph, test management) are added by DevSer
 
 Use this for local development with `adk web`.
 For production deployments, use api_server.py instead.
+
+Security: like ApiServer, every endpoint here is unauthenticated, and the
+dev-only endpoints additionally read and write agent files on disk and run
+evaluation and debugging code. This server is intended solely for local
+development on a trusted machine. Never expose it to an untrusted or public
+network, and never use it for a production or multi-user deployment.
 """
 
 from __future__ import annotations
@@ -185,6 +191,9 @@ class DevServer(ApiServer):
 
   Inherits all production endpoints from ApiServer and adds development-specific
   endpoints for evaluation, debugging, and developer UI features.
+
+  Like ApiServer, all endpoints are unauthenticated. This server is intended
+  for local development only and must not be exposed to untrusted networks.
   """
 
   _allow_special_agents: bool = True