I’m working through some LangGraph tutorials and having trouble getting the local development server to work properly. My notebooks run without any problems, but when I launch the dev server with the langgraph dev command, the graphs don’t appear in the browser interface.
The error message I keep getting is: “Failed to load assistants, please verify if the API server is running or accessible from the browser. TypeError: Failed to fetch”
I’ve been trying to fix this for the past day but can’t figure out what’s wrong with my setup. The code executes fine in Jupyter, so I’m not sure why the server won’t display the graphs correctly. Has anyone run into similar problems with the local development environment? Any suggestions would be really helpful.
This connectivity issue happens when your server binding doesn’t match what the client expects. I hit this same error a few weeks back with my LangGraph setup. My dev server was binding to 127.0.0.1, but the browser was trying to reach localhost - they don’t always resolve the same way depending on your system. Check if you can access the server directly using the exact IP and port from your terminal when you start it. Also check your firewall or antivirus - I’ve seen corporate security tools block local dev servers even when they look like they’re running fine.
I encountered a similar issue with LangGraph as well. In my experience, the problem often stems from local server configurations. Ensure your server is assigned to the appropriate localhost and port, and confirm you’re accessing the correct URL in the browser. Additionally, it might be worth inspecting your network settings, as they can often lead to such connectivity errors. Restarting your machine can sometimes resolve these issues as well. Typically, this is more an environmental issue rather than a flaw in the installation itself.
yeah, that’s def a CORS issue. langgraph’s dev server gets blocked by browser security policies sometimes. try running it with --host 0.0.0.0 when you start the server - that usually helps. also, check you ain’t got multiple instances running on diff ports.
Port conflicts cause this error 90% of the time. I’ve hit this exact issue tons of times with new team members.
Kill any hanging langgraph processes first. Run ps aux | grep langgraph and kill them all. Then check what’s using your ports: netstat -tulpn | grep :8123 (swap in your actual port).
Docker and other dev tools love stealing ports langgraph wants. Just had Jupyter grab port 8000 last week - same fetch errors you’re getting.
Start the server with a different port: langgraph dev --port 8124. The browser interface will show you the right URL when it boots up correctly.