glean/docs/user/error-reporting.md

Error reporting

The Glean SDK records the number of errors that occur when metrics are passed invalid data or are otherwise used incorrectly. This information is reported back in special labeled counter metrics in the glean.error category. Error metrics are included in the same pings as the metric that caused the error. Additionally, error metrics are always sent in the metrics ping ping.

The following categories of errors are recorded:

• invalid_value: The metric value was invalid or out-of-range.
• invalid_label: The label on a labeled metric was invalid.

For example, if you had a string metric and passed it a string that was too long:

MyMetrics.stringMetric.set("this_string_is_longer_than_the_limit_for_string_metrics")

The following error metric counter would be incremented:

Glean.error.invalidValue.add(1)

Resulting in the following keys in the ping:

{
  "metrics": {
    "labeled_counter": {
      "glean.error.invalid_value": {
        "my_metrics.string_metric": 1
      }
    }
  }
}

If you have a debug build of the Glean SDK, details about the errors being recorded are included in the logs. This detailed information is not included in Glean pings.