MQTT topic wildcard tester
Enter a subscription filter and a list of topics to see exactly which ones match — following the MQTT 3.1.1 and 5.0 rules for +, # and $ topics.
home/kitchen/temperaturematcheshome/kitchen/humidityno matchhome/garage/doorno matchhomeno matchoffice/kitchen/temperatureno match$SYS/broker/uptimeno match
Want to see it on a live broker? Subscribe with the same filter in the online MQTT client, or read the guide to MQTT topics and wildcards.
Wildcard FAQ
What does + mean in an MQTT topic?
The + wildcard matches exactly one topic level. home/+/temperature matches home/kitchen/temperature but not home/kitchen/sensor/temperature.
What does # mean in an MQTT topic?
The # wildcard matches any number of levels, including zero, and must be the last character of the filter. home/# matches home, home/kitchen and home/kitchen/temperature.
Why does # not match $SYS topics?
Topics starting with $ are reserved for broker-internal use. The MQTT specification says filters starting with a wildcard must not match them, so you must subscribe to $SYS/# explicitly.