adk web session 403 forbidden error

[luisgermanjedi]

Hello Folks, I know this issue sounds silly, but can't fix it so far. I am using Github codespaces, the agent runs well in the CLI, however when I open the web client and start a prompt got: "failed to create session" (in the web), this is the error in the command line:

INFO: Application startup complete.
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO: 79.155.29.187:0 - "GET / HTTP/1.1" 307 Temporary Redirect
INFO: 79.155.29.187:0 - "GET /dev-ui/assets/config/runtime-config.json HTTP/1.1" 200 OK
INFO: 79.155.29.187:0 - "GET /version HTTP/1.1" 200 OK
INFO: 79.155.29.187:0 - "GET /list-apps?relative_path=./ HTTP/1.1" 200 OK
INFO: 79.155.29.187:0 - "GET /builder/app/my_agent?ts=1777466446330 HTTP/1.1" 200 OK
INFO: 79.155.29.187:0 - "GET /dev/build_graph_image/my_agent?dark_mode=false HTTP/1.1" 404 Not Found
INFO: 79.155.29.187:0 - "GET /dev/build_graph_image/my_agent?dark_mode=true HTTP/1.1" 404 Not Found
2026-04-29 12:40:46,616 - INFO - envs.py:83 - Loaded .env file for my_agent at /workspaces/Google-ADK/my_agent/.env
2026-04-29 12:40:46,617 - INFO - envs.py:83 - Loaded .env file for my_agent at /workspaces/Google-ADK/my_agent/.env
2026-04-29 12:40:46,618 - INFO - agent_loader.py:131 - Found root_agent in my_agent.agent
INFO: 79.155.29.187:0 - "GET /dev/build_graph/my_agent HTTP/1.1" 200 OK
INFO: 79.155.29.187:0 - "POST /apps/my_agent/users/user/sessions HTTP/1.1" 403 Forbidden
INFO: 79.155.29.187:0 - "POST /apps/my_agent/users/user/sessions HTTP/1.1" 403 Forbidden

any idea ?

[haranrk]

Hey @luisgermanjedi! By default, the ADK web server only allows same-origin requests. To permit other origins, use the --allow_origins flag when starting the server. To allow all origins, run:

adk web --allow_origins="regex:.*"

[luisgermanjedi]

Thanks ! @haranrk that did the trick!