MQTT broker

An MQTT broker just for EMF, for all of your real-time data

MQTT is a pub-sub protocol for real-time data, popular in IoT and embedded scenarios because of how lightweight it is.

In MQTT, a “broker” is basically a server that you connect to, in order to read (subscribe) or write (publish) data on named topics. A topic has a name (such as emf/ducks)and a set of clients which are subscribed to it at any point in time.

We would love to see what you can share with the field over MQTT. Everything is readable by everyone, so prepare to embrace the openness but don’t share anything private!

MQTT doesn’t place any restrictions on what you send in payloads to a given topic. It could be UTF-8 text, JSON, or a binary message! Try to publish your data in a format that’s relatively easy to decode, though :)

Server connection details

Hostname: mqtt.emf.camp

Ports available:

  • 1883, no TLS (plaintext)
  • 8883, with TLS (encrypted)

You don’t need to authenticate, see below.

Topics and permissions

Anyone can subscribe to any topic. You could subscribe to everything if you wanted!

Without authenticating with a username/password, you can publish to topics beginning with open/. (This is a change from pre-2026 where anything except emf/... was publishable anonymously.)

Some event infrastructure is publishing to MQTT too, using other topic prefixes where publishing (but not subscribing) is protected with usernames & passwords. We use these to help run the event! There are also a number of installations and games doing cool things on MQTT.

Known topic namespaces

Check out topics under these prefixes, which might have something fun to look at:

  • bar/ – live stats from the bars at the Robot Arms and NullSector. See the Bar page for the full rundown of what’s published here.
    TL;DR: anything published over the bar system’s websocket API can also be found on MQTT.
  • weather/hq – live weather data from HQ. Full details on the Weather page.

Tips on topic naming, and wildcard subscriptions

Topics are best named hierarchically, because MQTT supports subscribing to entire groups of topics at once using wildcards.

For example, you could subscribe to all the bar data with one subscription to bar/#. The # wildcard works much like how an asterisk – * – works outside of MQTT, like in typical filename wildcards, but it can only appear at the end of a subscription.

There is also a + wildcard, which works at a single topic ’level’, that is, a bit of a topic name between slashes. For example, subscribing to fauna/+/count would subscribe to both fauna/ducks/count and fauna/spiders/count – if those topics existed ;)

Here is some further reading material on MQTT topic names and wildcard subscriptions: https://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices/

Last modified July 7, 2026: Make the MQTT page lead more truthful; the broker's in Slough (52898ec)