Source Tags

Tag all subsequent outgoing pings with a maximum of 5 comma-separated tags.

"To tag" a ping with Source Tags means that the ping request will contain the X-Source-Tags header with a comma separated list of the given tags.

Once enabled, the only way to disable this feature is to restart or manually reset the application.


  • Any valid HTTP header value is a valid source tag (e.g. any value that matches the regex [a-zA-Z0-9-]{1,20}) and values starting with the substring glean are reserved for internal Glean usage and thus are also considered invalid. If any value in the list of source tags is invalid, the whole list will be ignored.
  • If the list of tags has more than five members, the whole list will be ignored.
  • The special value automation is meant for tagging pings generated on automation: such pings will be specially handled on the pipeline (i.e. discarded from non-live views).



Sets the Source Tags to a given value.

This API can safely be called before Glean.initialize. The tag will be applied upon initialization in this case.

import mozilla.telemetry.glean.Glean

Glean.setSourceTags(setOf("my-tag", "your-tag", "our-tag"))
Glean.INSTANCE.setSourceTags(setOf("my-tag", "your-tag", "our-tag"))
import Glean

Glean.shared.setSourceTags(["my-tag", "your-tag", "our-tag"])
use glean;

glean.set_source_tags(["my-tag", "your-tag", "our-tag"]);
import Glean from "@mozilla/glean/<platform>";

Glean.setSourceTags(["my-tag", "your-tag", "our-tag"]);

Environment variable


It is also possible to set the debug view tag through the GLEAN_SOURCE_TAGS environment variable.

This variable must be set at runtime, not at compile time. It will be checked upon Glean initialization.

Xcode IDE scheme editor popup screenshot

To set environment variables to the process running your app in an iOS device or emulator you need to edit the scheme for your app. In the Xcode IDE, use the shortcut Cmd + < to open the scheme editor popup. The environment variables editor is under the Arguments tab on this popup.

$ GLEAN_SOURCE_TAGS=my-tag,your-tag,our-tag python
$ GLEAN_SOURCE_TAGS=my-tag,your-tag,our-tag cargo run
$ GLEAN_SOURCE_TAGS=my-tag,your-tag,our-tag ./mach run