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Subscribing to topics

A client can subscribe to the exact topic of a published message. It can also use wildcards to subscribe to multiple topics simultaneously. There are two wildcards available:

Single level (+)


For the one topic level where the + wildcard is placed, any string matches.

Multi level (#)

A multi-level wildcard can only be placed as the last character in the topic. E. g.:


All topics that begin with my-module/my-category/ are subscribed now.

Special characters

There are only one reserved character (apart from /): $. Don't use it. In general try to use lower-case ASCII character and no spaces wherever possible.

Best practices

Never use a leading forward slash

This would introduce an additional unnecessary topic level.

Use lower-case ASCII characters

Like this topics always work. Also try to avoid spaces.

Use specific topics - don't subscribe to #

This would create a huge load. Try to specify the required topics as exact as possible.