Peter Scargill has written an article ‘the world of MQTT on ESP8266:
The obvious choice was a local copy of MOSQUITTO – the free package designed, apparently by Roger Light. A simple DOS application which can also act as a service. Marvellous. Now I needed to put the code into the ESP8266 – that worked – marvellous. I even developed my own little client application (well, I tarted up a demo) on Basic 4 Android (B4A). Now I needed some PC client to test the messages… not so marvellous. The command line tools provided with Mosquitto are, well, command line tools – I may be 60 but I’m still part of the pretty-coloured-buttons generation – I really would rather have as little to do with black boxes as possible. At least half of the links I tried on the web went to projects that haven’t started yet, or old ones that were dead – or just no-where. I finally settled on MQTT-SPY and I have to say.. it’s lovely both in operation and visually. MQTT messages are really trivial comprising a topic – and some content. I set up Mosquitto, subscribed to an arbitrary topic – and sent a message to it. LO AND BEHOLD it appeared at the bottom of MQTT-SPY.