Fix Claude Connection Failed & Network Errors

When using Claude.ai, you may encounter an on-screen banner reading "Connection failed" or "Network connection lost." Unlike simple server-side downtime, these errors usually mean the browser's persistent network connections (specifically WebSockets or Server-Sent Events, which Claude uses to stream responses in real-time) have been blocked or interrupted.

To restore your connection to Claude, follow these sequential steps to diagnose and repair local network, firewall, and browser socket configurations.

Step 1: Verify WebSocket and HTTP/2 Compatibility

Claude's chat interface relies on active WebSockets (wss://) to stream text word-by-word. If your network or browser blocks persistent connections, Claude will fail to complete responses.

1. Open a new tab and visit a WebSocket testing site such as websocketstest.com.
2. Let the diagnostic test run. If the test indicates that WebSockets are blocked or port 80 / 443 is closed, your current network setup is preventing Claude from communicating with its API.
3. If WebSockets are blocked, proceed to Step 2 to configure your network settings.

Step 2: Deactivate Local VPNs and iCloud Private Relay

Routing tools like virtual private networks (VPNs) and macOS's iCloud Private Relay can split or drop persistent TCP connections, causing Claude's interface to throw a connection failed error.

1. Disable your VPN client: Completely quit your VPN application.
2. Disable iCloud Private Relay (Mac/iOS): Go to System Settings > [Your Name] > iCloud > Private Relay and toggle it Off.
3. Reload the Claude web page and attempt to send a message to see if the connection is restored.

Step 3: Whitelist Anthropic Domains in Firewall and Security Software

Local antivirus software, anti-malware tools (such as Malwarebytes), and corporate firewalls can mistakenly block the background connections Claude uses for real-time data streaming.

1. Open your firewall or antivirus control panel.
2. Navigate to the Web Protection, Exclusions, or Whitelist settings.
3. Add exceptions for the following domains (include the asterisks for wildcards if supported):
4. *.claude.ai
5. *.anthropic.com
6. cdn.usefathom.com (if used for tracking/analytics resolution)
7. Save the changes, restart your browser, and test the connection.

Step 4: Switch to a Public DNS Resolver

Local ISP DNS servers can sometimes experience routing failures or slow resolutions for Anthropic's globally distributed servers. Switching your network DNS to a reliable public resolver can restore connectivity.

On Windows: 1. Open the Control Panel and go to **Network and Sharing Center** > **Change adapter settings**. 2. Right-click your active connection (Wi-Fi or Ethernet) and select **Properties**. 3. Select **Internet Protocol Version 4 (TCP/IPv4)** and click **Properties**. 4. Choose **Use the following DNS server addresses** and enter: * Preferred: `1.1.1.1` (Cloudflare) * Alternative: `8.8.8.8` (Google) 5. Click **OK** to apply.

On macOS: 1. Go to **System Settings** > **Network**. 2. Click your active connection, then click **Details**. 3. Select the **DNS** tab on the left. 4. Click the **+** icon under the DNS Servers list and add `1.1.1.1` and `8.8.8.8`. 5. Click **OK** to save.

Step 5: Test via Mobile Hotspot

To determine if the connection issue is localized to your router or local ISP configuration, perform a network isolation test.

1. Disconnect your computer from your primary Wi-Fi or Ethernet network.
2. Enable the Mobile Hotspot feature on your cellular phone.
3. Connect your computer to your phone's cellular hotspot.
4. Navigate to Claude.ai and check if you can send prompts without a connection error. If this works, your primary router’s firewall, Parental Controls, or ISP routing settings are blocking the site.

When to escalate

If the connection failed error persists across multiple distinct internet connections (e.g., both home Wi-Fi and mobile data) and on different devices (computer and phone), check status.anthropic.com to see if there is an active system-wide API or WebSocket degradation. If all services are green, clear your browser's local storage and reach out to Anthropic's billing or technical support via the help widget on the main site, as your specific IP address block or account token might be flagged for review.