Connecting
The top bar shows host:port, TLS status and the MQTT version.
Click the pencil to edit settings or the plug to connect or disconnect.
The plug’s colour shows the connection state; hover for details or an error.
| Colour | State |
|---|---|
| Green | Connected |
| Yellow | Connecting or reconnecting |
| Red | Failed |
| Grey | Disconnected |
Dropped connections retry every second. Failed stops retries for errors that would recur, such as an oversized packet.
Connection settings
Connect saves settings and starts a new connection, ending any existing one.
Cancel or Esc discards edits.
| Setting | Default | Notes |
|---|---|---|
| Host, Port | localhost, 1883 | TCP only; no WebSockets. |
| TLS | off | See TLS. |
| MQTT version | 3.1.1 | Choose 5 for MQTT 5 properties. |
| Client id | rstmqtt- + 8 random hex digits | Reusing another client’s id disconnects it. |
| Username, Password | empty | Passwords are never saved, and clear when the broker, TLS setting or username changes. |
| Keep alive | 30 s | MQTT 5 uses at least 5 s. |
| Clean session | on | See Persistent sessions. |
Client id, username and password cannot contain null characters or exceed 65,535 bytes. Errors name the offending field.
TLS
Enable TLS for an encrypted connection with certificate and hostname verification.
Set the port yourself, usually 8883.
System root certificates are trusted by default. For a private CA, set CA file to a PEM file containing its certificates; this replaces the system roots. Client certificates and skipping verification are not supported.
Subscriptions
Each Subscriptions row pairs a topic filter with a QoS level.
The defaults, # and $SYS/# at QoS 0, cover all topics, including broker statistics.
Use Add subscription or the minus button to add or remove rows.
Wildcards occupy whole levels: + matches one, and a final # matches the rest, as in home/+/temperature or home/#.
Invalid filters turn red; hover for the reason. Broker rejections appear in the status bar.
Retained messages fill the tree with the broker’s last known values when you subscribe.
Persistent sessions
Uncheck Clean session to keep subscriptions and queued QoS 1 and 2 messages on the broker while disconnected. Reuse the client id to resume. MQTT 5 sessions never expire unless the broker caps them; an empty client id always uses a clean session.
rstmqtt remembers the last persistent session’s filters and unsubscribes removed filters when you reconnect to that session.