Most error patterns in Claude Desktop have known causes. Before I touch the configuration, I take three diagnostic steps – that saves considerable time in practice.
Three diagnostic steps first
Open the log file. On macOS under ~/Library/Logs/Claude, on Windows in %APPDATA%Claudelogs, on Linux under ~/.config/Claude/logs. The last 50 lines reveal the problem in most cases.
Check the Anthropic status. A glance at status.anthropic.com rules out that the error lies outside your own setup. That tends to save hours of misdirected searching.
Isolate the network path. Tethering via your phone quickly shows whether VPN, proxy, or Zscaler is responsible. If the app works on the hotspot, you know where to look.
Symptom index: the most common error patterns
Black or blank screen on start. Cause: GPU conflict or corrupted cache. Delete the cache directory, disable hardware acceleration, restart.
App loads endlessly, spinner turns. Cause: network blockade by VPN, proxy, or Zscaler. Allow api.anthropic.com, test briefly without VPN.
403 Forbidden or “invalid authorization”. Cause: token expired or region header altered. Create a new token, check plan status, examine the proxy for header manipulation.
500 Internal Server Error. Cause: a server problem on Anthropic’s side. Check status.anthropic.com, retry after five minutes.
Hammer icon missing, no MCP servers visible. Cause: syntax error in claude_desktop_config.json or wrong command path. Run a JSON lint, set paths absolute, restart the app completely.
App starts, closes immediately on Linux. Cause: missing system libraries. Start the app from the terminal, read the error message, install the missing packages.
What often goes wrong on a corporate network
Zscaler. When Zscaler re-signs the traffic, Claude Desktop rejects the certificate. Solution: exclude api.anthropic.com from TLS inspection or place the Zscaler root certificate in the system trust store.
Intune. App packages for Intune need the right detection path. Skip it, and you only see the app on devices after manual intervention.
Authenticated proxy. Set HTTPS_PROXY and HTTP_PROXY in the system context, not only in the user shell. Otherwise the app does not use the proxy and runs into timeouts.
Frequently asked questions
What do I check first when Claude Desktop is unresponsive?
Three steps: open the log file, check status.anthropic.com and isolate the network path. In practice this saves a lot of time.
Where do I find the log files?
On macOS under ~/Library/Logs/Claude, on Windows under %APPDATA%Claudelogs, on Linux under ~/.config/Claude/logs. The last 50 lines usually reveal the cause.
The app loads endlessly – why?
Usually a network block from VPN, proxy or Zscaler. Allow api.anthropic.com and test briefly without the VPN.
I see a black or empty screen. What helps?
That points to a GPU conflict or a corrupted cache. Delete the cache directory, disable hardware acceleration and restart.