Private Network Access Blocking LangSmith Studio Connection

Last updated: November 20, 2025

Starting with Chrome version 142, users may experience "Failed to initialize Studio" errors with "TypeError: Failed to fetch" when trying to connect LangSmith Studio to their local development server via langgraph dev. This occurs even when the API server at http://127.0.0.1:2024/docs loads successfully.

Root Cause: Chrome 142 fully enforces the Private Network Access (PNA) specification with no fallback, which blocks HTTPS sites (like https://smith.langchain.com) from accessing HTTP localhost servers by default.

Symptoms

  • Running langgraph dev or langgraph dev --allow-blocking starts the server successfully

  • Navigating to http://127.0.0.1:2024/docs shows the API documentation correctly

  • LangSmith Studio at https://smith.langchain.com shows: "Failed to initialize Studio - Please verify if the API server is running or accessible from the browser. TypeError: Failed to fetch"

  • Browser console shows errors like: Permission was denied for this request to access the 'unknown' address space

Solution

Quick Fix: Allow Local Network Access in Chrome

  1. Open LangSmith Studio at https://smith.langchain.com in Chrome

  2. Click the lock icon (or site information icon) to the left of the address bar

  3. Look for the "Local network access" option in the dropdown

  4. Change the setting from "Ask (default)" or "Block" to "Allow"

  5. Reload the page

The Studio should now connect to your local development server successfully.

Additional Troubleshooting

Check for Browser Extension Conflicts

Browser extensions (especially Ollama Chrome extension or AI model extensions) can interfere with localhost connections:

  1. Disable all browser extensions temporarily

  2. Restart Chrome

  3. Try connecting to Studio again

  4. If it works, re-enable extensions one by one to identify the culprit

Verify Dependencies Are Up to Date

pip install -U "langgraph-cli[inmem]"

Clear Browser Cache and Site Data

  1. In Chrome, go to Settings > Privacy and Security > Site Settings

  2. Find https://smith.langchain.com in the list

  3. Click "Clear data"

  4. Restart Chrome and try again