Tachyon client devices can have a number of custom tags assigned using Tachyon and the Tachyon clients. There are two types of tag: Device tags, which can be used in the scopes for questions and actions to help target specific collections of devices; and freeform tags that can be queried and set using specific questions and actions.

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Device versus freeform tags

Tachyon supports two kinds of tag that can be used to set properties on Tachyon client devices. The Tachyon client stores both types of tag in persistent storage. Values are set or deleted using actions and queried using questions. The differences are described below.

Tag typeDescription

Can also be used when defining the coverage for questions and actions. A Tachyon Full Administrator must define the names and values for Device tags before they can be applied to devices using Device tag actions.

Once set by an action, the Tachyon client reports device tags back to the System where they are stored in the Tachyon Master database for each device, which is how they can be used to define coverage for questions and actions.

The Tachyon client regularly reports back its list of tags. The list consists of a separator and name=value for each tag plus a final separator at the end of the list. The entire list of name=value pairs and their separators must not exceed 511 bytes. Any tags that exceed this limit are not reported back. Only the tags reported back by each Tachyon client can be used for coverage. Therefore, the length of tag names and values should be kept short if many different tags are to be used. The maximum length of a tag name is 16 characters, and the maximum length of a tag value is 32.

More details on the Coverage tag workflow are given below, including links to associated tutorials.


Cannot be used when defining the coverage for a question.

Freeform tags can be set with arbitrary names and values that are defined only when running a Freeform tag action.

There is no limit to the number of freeform tags or the length of the list, and no limit to the length of tag name or tag value.

Tag names are case-insensitive. Tag values are not case-sensitive, and case is preserved.

Please refer to Tachyon SDK - Tags for how to use tagging methods when writing your own Tachyon instructions.

The Device tag workflow

You create and manage Device tags using the Custom properties page in Settings→Configuration

Tachyon enables Device tag properties to be created and set on Tachyon client devices, which can then be used when setting the coverage for a question. The basic workflow is:

  1. A Tachyon Full Administrator defines the name of a Device tag and one or more associated values. See Adding properties - tutorial for more details on this step.
  2. Actioners with permissions to the Tachyon client tags product pack run actions that use the defined properties and values and assign them to particular Tachyon client devices. See Actions to set tags - tutorial for more details on this step.
  3. Questioners can then use the Tags parameter, when defining the coverage for a question, to constrain the coverage to particular properties and values thereby targeting particular Tachyon client devices. See Using tags to set the coverage for a question - tutorial for more details on this step.