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System labels in Synthetic Monitoring

Synthetic Monitoring applies a set of labels to the metrics and logs that your checks generate. These system labels identify the check, the probe, and details of each result, and power features in the Synthetic Monitoring app.

This page is a complete reference of the labels Synthetic Monitoring generates. All of these labels are reserved: you can’t use their names as custom labels on your checks or private probes. This prevents your labels from colliding with the labels that Synthetic Monitoring writes to the same metrics and logs.

Reserved system labels

The following label names are reserved for system use.

Common metric labels

These labels appear on every check metric, for every check type.

Together, job, instance, probe, and config_version uniquely identify a check result.

The sm_check_info metric

The labels of the sm_check_info metric provide additional information about the check. Query sm_check_info with other check metrics by joining on the common metric labels.

Histogram metrics

Duration metrics for DNS, HTTP, k6 scripted, MultiHTTP, and ping checks

TLS metrics

TLS metrics are generated by check types that inspect TLS connections and certificates, such as HTTP and TCP checks.

k6-based check metrics

These labels appear on metrics from k6 scripted, MultiHTTP, and k6 browser checks.

HTTP request metrics

These labels appear on HTTP request metrics from k6-based checks.

k6 browser-based check metrics

Check logs

The instance, job, and probe labels are the same common labels that appear on check metrics. Check logs carry the following labels.

What happens if you use a reserved label

The Synthetic Monitoring API enforces the reserved label names when you create or change checks and private probes:

If a check or probe uses a reserved label name, the API rejects the request with an error that identifies the conflicting label. Rename the label to save your changes. You can always disable or delete a check, even if it uses a reserved label name.

If you manage checks with Terraform or the API, rename reserved labels in your check definitions. To rename a label key across every check in your tenant in a single request, use the Synthetic Monitoring API POST /api/v1/check/labels/{key} endpoint. For more information about managing checks as code, refer to Provision Synthetic Monitoring resources.

When a k6 tag uses a reserved label

Tags that you define in a k6 script aren’t validated against the reserved label names, because Synthetic Monitoring doesn’t inspect the contents of your script. If a k6 tag name collides with a reserved system label name, Synthetic Monitoring overwrites your tag value with its own value on metrics. Check logs are unaffected, because k6 tags aren’t indexed as labels.

For more information about how k6 tags appear on your data, refer to the k6 compatibility section of the k6 scripted and k6 browser check documentation.

When an existing label becomes reserved

Synthetic Monitoring occasionally reserves new label names after your tenant has migrated, for example when a new check type introduces new metrics. This is different from the initial label migration, which requires you to rename any labels that collide with existing reserved names before you can proceed.

If a label you already use becomes reserved later:

• Your label keeps working. Your checks continue to run and emit your value for that label. Synthetic Monitoring doesn’t overwrite or drop your data.
• System features tied to the new label don’t apply to affected checks. Any new functionality that depends on the reserved label is unavailable for checks that carry your conflicting label, until you rename it.
• The API blocks edits to affected checks. Updates to a check that carries the conflicting label are rejected until you rename the label. The check continues to run in the meantime, and you can still disable or delete it.
• In-app warnings identify affected checks. The Synthetic Monitoring app flags checks with label conflicts so you can find and fix them.