# Resolving "Connection Lost" message

The "Connection lost" message means GitBook can't establish the network connections it needs. This is usually caused by something on your computer or network blocking the connection.

Common causes include browser extensions, firewalls, security software, proxies, and temporary network issues in your area.

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### **Troubleshooting steps**

Work through these steps in order until the issue is resolved.

1. **Clear your cache and restart your browser.** This resolves most temporary connection issues.
2. **Restart your Wi-Fi or ethernet connection.** Turn your connection off and back on, then try again.
3. **Try a different browser or device.** If GitBook works elsewhere, the issue is specific to your original setup. Contact support and let us know which browser you were using.
4. **Disable browser extensions.** Extensions — especially those that block content or manage network requests — can interfere with GitBook. Try disabling them one by one to identify the cause.
5. **Check your firewall or security software.** If your network blocks any of the domains GitBook relies on, see the safelisting section below.

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**Safelisting GitBook's domains**

If a firewall or security application is blocking traffic, add the following domains to your allowlist.

**GitBook app**

* `*.gitbook.com`
  * `app.gitbook.com`
  * `api.gitbook.com`
  * `clearbit-risk.gitbook.com`
  * `files.gitbook.com`
  * `segment-cdn.gitbook.com`
  * `segment-api.gitbook.com`
* `*.gitbook.io`

**CDNs**

* `cdn.iframe.ly`
* `cdn.polyfill.io`

**Google APIs**

* `*.googleapis.com`
  * `firebase.googleapis.com`
  * `firestore.googleapis.com`
  * `www.googleapis.com`
* `*.googleusercontent.com`
* `*.googletagmanager.com`

**Sentry** (error monitoring)

* `*.sentry.io`

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If the issue persists after working through all of these steps, contact GitBook support. Include details about your browser, device, and network setup so we can investigate.