Diagnose a broker connection

Find a connection error, copy the relevant log lines and check recovery.

About 3 minutes · MQTT Viewer 1.2 · Web UI screenshots

Before you start

Use a connection you can safely reconnect. The example first targets a closed local port, then restores the disposable broker’s listening port.

1. Open the connection logs

Open the connection name menu and choose View logs. The Client logs dialog shows connection and subscription activity for that connection.

2. Find and copy the error

Type a term in Filter logs. Toggle DEBUG, INFO, WARN or ERROR to show or hide a level. Click Copy to copy the lines matching your current filters.

Client logs filtered to a connection refused error on a local test port — This test deliberately used a closed port. Full size (opens in a new tab)

3. Correct the connection and retry

Close the logs. Open Edit connection…, disconnect if necessary and correct the host, port or other relevant setting. Click Connect, then reopen View logs and clear the text filter to inspect the new activity.

Client logs after correcting the port and reconnecting to the test broker — The connected state confirms the retry succeeded. Full size (opens in a new tab)

If the dialog looks empty

Clear the text filter and turn the level buttons back on. Enable Debug logging only when you need more detail. Clear removes the displayed log history; it does not repair a connection or clear MQTT messages.