Fix Claude 'Connection Lost. Please Retry' Error

While using the Claude web interface (claude.ai), a red or orange banner reading "Connection lost. Please retry." can interrupt your session. This error occurs when the persistent WebSocket connection or Server-Sent Events (SSE) stream between your web browser and Claude's backend engines drops. Because Claude streams responses token-by-token in real-time, any network instability or local browser interference can instantly trigger this banner. Follow these steps to diagnose and re-establish a stable connection.

1. Force a Cache-Bypassing Hard Reload

Standard browser reloads often pull assets from local storage, preserving corrupted connection states. You need to force the browser to establish a completely fresh handshake with Claude's servers.

• Chrome, Edge, and Firefox (Windows): Press Ctrl + F5, or hold Ctrl and click the Reload icon.
• Chrome and Firefox (macOS): Press Cmd + Shift + R, or hold Shift and click the Reload icon.
• Safari (macOS): Press Option + Cmd + E to empty the cache, then press Cmd + R to refresh the page.

2. Inspect WebSocket Blocks in Developer Tools

Claude relies heavily on WebSockets to maintain real-time bidirectional communication. If your network blocks WebSockets, the page will load, but sending a prompt will fail with a connection error.

1. Open your browser's Developer Tools by pressing F12 (or Cmd + Option + I on Mac).
2. Navigate to the Network tab.
3. Filter the network requests by selecting WS (WebSockets) or typing transport=websocket in the search filter.
4. Type a short prompt in Claude and press Enter.
5. Watch the active WebSocket connection. If it immediately turns red or shows a status of Closed or 403, your local network configuration or an active software suite is blocking real-time WebSocket traffic.

3. Configure Local Security Software and Extensions

Aggressive local security settings can actively dissect and terminate persistent streaming connections.

• Disable Content Blockers: Ad-blockers like uBlock Origin, AdBlock Plus, or Brave Shields can misidentify Claude's streaming scripts as tracking mechanisms. Add claude.ai to your extension's whitelist or turn the extension off entirely to test.
• Check Antivirus SSL/TLS Inspection: Security suites (such as Kaspersky, Bitdefender, or Avast) use "Web Protection" features that decrypt and inspect secure web traffic. This process breaks long-lived WebSocket connections. Temporarily disable "Encrypted connections scanning" or "HTTPS inspection" in your antivirus settings.
• Deactivate VPNs and Proxies: Virtual Private Networks (VPNs) and proxy servers often have strict timeout thresholds that kill idle TCP/IP connections. Turn off your VPN or switch to a different server location to rule this out.

4. Bypass Corporate Firewalls

If you are accessing Claude from an enterprise or school network, the network administrator may have implemented Deep Packet Inspection (DPI) policies that flag long-lived streaming connections as anomalous traffic.

• Test via Cellular Hotspot: Disconnect your computer from the local enterprise network and tether it to your mobile phone's cellular hotspot. If Claude connects successfully without dropping, the issue lies entirely with the enterprise firewall's routing restrictions.
• Request Whitelisting: Ask your network administrator to allow outgoing WebSocket traffic and to whitelist the following domains:
• *.claude.ai
• *.anthropic.com

When to escalate

If you have verified that WebSockets are functioning on other platforms, disabled all extensions, flushed your DNS, and still get the "Connection lost" banner across multiple networks (both Wi-Fi and mobile data), the underlying server cluster hosting your chat session may be suffering a regional routing node failure. Click the ? (Help) icon in the bottom corner of the Claude web interface to report the bug, specifying your browser version, operating system, and whether the issue occurs on other browsers.