Tags YAML Registry Format

Any number of custom "tags" can be added to any metric or ping. This can be useful in data discovery tools like the Glean Dictionary. The tags for an application are defined in YAML files which follow the tags.yaml JSON schema.

These files must be parsed by glean_parser at build time in order to generate the metadata.

For more information on how to introduce the glean_parser build step for a specific language / environment, refer to the "Adding Glean to your project" section of this book.

Note on the naming of these files

Although we refer to tag definitions YAML files as tags.yaml throughout Glean documentation this files may be named whatever makes the most sense for each project and may even be broken down into multiple files, if necessary.

File structure

# Schema
$schema: moz://mozilla.org/schemas/glean/tags/1-0-0

  description: Metrics or pings in the "search" domain


Declaring the schema at the top of a tags definitions file is required, as it is what indicates that the current file is a tag definitions file.


Tag names are the top-level keys on tag definitions files. One single definition file may contain multiple tag declarations.

There is no restriction on the name of a tag, aside from the fact that they have a maximum of 80 characters.

Tag parameters

Required parameters


A textual description of the tag. It may contain markdown syntax.