ADK WEB command on Google Cloud Shell Terminal

[sf0622]

I am doing everything online in Google Cloud Shell Editor/Terminal

The agent code in agent.py, what I am running is fairly simple:

---

from google.adk.agents.llm_agent import Agent
root_agent = Agent(
model='gemini-3.5-flash',
name='root_agent',
description='An Agent that helps with History Lessons',
instruction='When asked about a topic, summarize the answer in bullet points, and provide a 5-line crisp summary at the end'
)

---

As far as I can tell, everything is setup correctly on GCP Agent Platform, including enabling API to Agent Platform, and linking project to a billing account.

TERMINAL INPUT/OUTPUT BELOW
Entering command “web adk” from the agent directory (agent directory is history_agent), terminal output pasted below:

shajifarooq@cloudshell:~/adk_course/test_agent/history_agent (adk-01-501323)$ adk web
2026-07-07 17:05:52,482 - INFO - service_factory.py:266 - Using in-memory memory service
2026-07-07 17:05:52,482 - INFO - local_storage.py:88 - Using per-agent session storage rooted at /home/shajifarooq/adk_course/test_agent
2026-07-07 17:05:52,483 - INFO - local_storage.py:120 - Using per-agent artifact storage rooted at /home/shajifarooq/adk_course/test_agent
/home/shajifarooq/.local/lib/python3.12/site-packages/google/adk/cli/fast_api.py:553: UserWarning: [EXPERIMENTAL] InMemoryCredentialService: This feature is experimental and may change or be removed in future versions without notice. It may introduce breaking changes at any time.
credential_service = InMemoryCredentialService()
/home/shajifarooq/.local/lib/python3.12/site-packages/google/adk/auth/credential_service/in_memory_credential_service.py:33: UserWarning: [EXPERIMENTAL] BaseCredentialService: This feature is experimental and may change or be removed in future versions without notice. It may introduce breaking changes at any time.
super().init()
INFO: Started server process [8518]
INFO: Waiting for application startup.

+-----------------------------------------------------------------------------+
| ADK Web Server started |
| |
| For local testing, access at http://127.0.0.1:8000/. |
+-----------------------------------------------------------------------------+

INFO: Application startup complete.
INFO: Uvicorn running on http://127.0.0.1:8000/ (Press CTRL+C to quit)

Once the Web Interface is opened via the link provided, following messages appear in the terminal:

INFO: 127.0.0.1:60488 - "GET / HTTP/1.1" 307 Temporary Redirect
INFO: 127.0.0.1:60488 - "GET /dev-ui/ HTTP/1.1" 304 Not Modified
INFO: 127.0.0.1:60488 - "GET /dev-ui/assets/config/runtime-config.json HTTP/1.1" 200 OK
INFO: 127.0.0.1:60488 - "GET /dev-ui/prism-dark.css HTTP/1.1" 404 Not Found
INFO: 127.0.0.1:60488 - "GET /list-apps?relative_path=./ HTTP/1.1" 200 OK
INFO: 127.0.0.1:60496 - "GET /version HTTP/1.1" 200 OK
2026-07-07 17:37:25,832 - INFO - envs.py:83 - Loaded .env file for history_agent at /home/shajifarooq/adk_course/test_agent/history_agent/.env
2026-07-07 17:37:25,833 - INFO - envs.py:83 - Loaded .env file for history_agent at /home/shajifarooq/adk_course/test_agent/history_agent/.env
2026-07-07 17:37:25,834 - INFO - agent_loader.py:169 - Found root_agent in history_agent.agent
INFO: 127.0.0.1:60488 - "GET /dev/apps/history_agent/build_graph_image?dark_mode=true HTTP/1.1" 200 OK
INFO: 127.0.0.1:60496 - "GET /dev/apps/history_agent/build_graph HTTP/1.1" 200 OK
INFO: 127.0.0.1:60512 - "GET /dev/apps/history_agent/build_graph_image?dark_mode=false HTTP/1.1" 200 OK
INFO: 127.0.0.1:60514 - "GET /dev/apps/history_agent/builder?ts=1783445846208 HTTP/1.1" 200 OK
INFO: 127.0.0.1:60496 - "GET /dev/apps/history_agent/eval_sets HTTP/1.1" 200 OK
INFO: 127.0.0.1:60488 - "GET /dev/apps/history_agent/eval_results HTTP/1.1" 200 OK

The web interface is unable able to activate a session to prompt the agent

INFO: 127.0.0.1:53106 - "POST /apps/history_agent/users/user/sessions HTTP/1.1" 403 Forbidden

[shajifarooq-oss]

Figured it out.

Problem 1: Gemini 3.5 is not available in the US region, hence the 404 error
Problem 2. Error 403 is caused by a CORS conflict, caused by Cloud Shell. Resolved by running the Bash command
" adk web --allow_origins="*" "

It is working now!

[surajksharma07]

@sf0622 Nice diagnosis — and it's not your setup, it's a side effect of the loopback DNS-rebinding guard we shipped in 2.4.0.
--allow_origins="" works, but since that opens CORS to literally anything, you might feel safer scoping it to just Cloud Shell: --allow_origins="regex:https://..cloudshell.dev".

Could you try that narrower version and confirm it still clears the 403 ?

[shajifarooq-oss]

Tried the more restrictive command you suggested - unfortunately, that does not work. Getting a 403 Error.

[shajifarooq-oss]

I think you meant the following command:

adk web --allow_origins="regex:https://..cloudshell.dev"

Let me know if you meant something else. The above command definitely does not work, but the broader command with "*" does.