The baseline ping


This ping is intended to provide metrics that are managed by the library itself, and not explicitly set by the application or included in the application's metrics.yaml file. If the application crashes no baseline ping is sent, no additional ping is generated with the data from before the crash.

Note: As the baseline ping was specifically designed for mobile operating systems, it is not sent when using the Glean Python bindings.


The baseline ping is automatically sent when the application is moved to the background.


The baseline ping includes the following fields:

Field nameTypeDescription
durationTimespanThe duration, in seconds, of the last foreground session. 1
localeStringThe locale of the application.

A quick note about the duration metric: it measures specifically the time that the user spent in the last foreground session. This is distinct from the start_time and end_time values (on every ping), which measure the ping lifetime. start_time is always set to be the time the previous ping of the same type was sent, so the span from start_time to end_time is normally longer than the span measured by duration.

  ↑   ↓           ↑          ↓
      start_time             end_time

  ↑ = foreground
  ↓ = background

The baseline ping shall also include the common ping sections found in all pings.

Querying ping contents

A quick note about querying ping contents (i.e. for Each metric in the baseline ping is organized by its metric type, and uses a namespace of glean.baseline. For instance, in order to select duration you would use metrics.timespan['glean.baseline.duration']. If you were trying to select a String based metric such as os, then you would use metrics.string['glean.baseline.os']

Example baseline ping

  "ping_info": {
    "ping_type": "baseline",
    "experiments": {
      "third_party_library": {
        "branch": "enabled"
    "seq": 0,
    "start_time": "2019-03-29T09:50-04:00",
    "end_time": "2019-03-29T09:53-04:00"
  "client_info": {
    "telemetry_sdk_build": "0.49.0",
    "first_run_date": "2019-03-29-04:00",
    "os": "Android",
    "android_sdk_version": "27",
    "os_version": "8.1.0",
    "device_manufacturer": "Google",
    "device_model": "Android SDK built for x86",
    "architecture": "x86",
    "app_build": "1",
    "app_display_version": "1.0",
    "client_id": "35dab852-74db-43f4-8aa0-88884211e545"
  "metrics": {
    "string": {
      "glean.baseline.locale": "en-US"
    "timespan": {
      "glean.baseline.duration": {
        "value": 52,
        "time_unit": "second"