[Google Chrome] CORS errors and "unable to connect to data plane" in hybrid deployments

Issue

Specifically when using Google Chrome - While trying to view experiments, datasets, or logs in the Braintrust web application, you notice "Your browser is unable to connect to the data plane at <custom-domain>" message at the top of the page, along with CORS errors in the browser console Network tab. You may also see a Failed to fetch error in the UI.

Cause

Chrome's local network access security feature blocks public websites (like www.braintrust.dev) from connecting to resources on private network addresses by default. When your data plane is hosted on an internal domain, Chrome prevents the connection unless explicitly allowed.

Resolution(s)

If you can modify Chrome settings (individual users or non-managed browsers)

1. Navigate to Chrome site settings for Braintrust

   Open Chrome and go to: chrome://settings/content/siteDetails?site=https://www.braintrust.dev

2. Enable local network access

   Scroll down to "Additional permissions" section, find "Allow local network access" and change it to Allow

3. Refresh the Braintrust page

   Reload www.braintrust.dev to apply the new permission setting

  Otherwise, if Chrome settings are managed by enterprise policies

1. Try an alternative browser

   Use Firefox or Edge, which may have different local network access policies

2. Contact your IT/Network team

   Request that www.braintrust.dev be allowlisted for local network access via Chrome enterprise policy, or ask if the data plane endpoint can be configured to use a public domain instead of a private network address

3. Apply the enterprise policy or configuration change

   Once IT has made the changes, restart your browser and test access