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Allow using double-underscores for federation #2839

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Allow using double-underscores for federation #2839

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2 changes: 1 addition & 1 deletion docs/specs/om/open_metrics_spec_2_0.md
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Expand Up @@ -110,7 +110,7 @@ Strings MUST only consist of valid UTF-8 characters and MAY be zero length. NULL

Labels are key-value pairs consisting of strings.

Label names beginning with two underscores are RESERVED and MUST NOT be used unless specified by this standard. Label names SHOULD follow the restrictions in the ABNF section under the `label-name` section. Label names MAY be any quoted escaped UTF-8 string as described in the ABNF section. Be aware that exposing UTF-8 metrics is still experimental and may reduce usability.
Label names beginning with two underscores are RESERVED for use for metric metadata. Label names beginning with two underscores MAY be used in cases where metrics could have conflicting metadata, such as federation, but MUST NOT be used otherwise. Label names SHOULD follow the restrictions in the ABNF section under the `label-name` section. Label names MAY be any quoted escaped UTF-8 string as described in the ABNF section. Be aware that exposing UTF-8 metrics is still experimental and may reduce usability.
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@bwplotka bwplotka Feb 11, 2026

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Label names beginning with two underscores are RESERVED for use for metric metadata. Label names beginning with two underscores MAY be used in cases where metrics could have conflicting metadata, such as federation, but MUST NOT be used otherwise. Label names SHOULD follow the restrictions in the ABNF section under the `label-name` section. Label names MAY be any quoted escaped UTF-8 string as described in the ABNF section. Be aware that exposing UTF-8 metrics is still experimental and may reduce usability.
Label names beginning with two underscores are RESERVED and MUST NOT be used unless specified by this standard. Such Label names MAY be used in cases where MetricFamilies' metadata might otherwise be conflicting, such as a federation cases.
Label names SHOULD follow the restrictions in the ABNF section under the `label-name` section. Label names MAY be any quoted escaped UTF-8 string as described in the ABNF section. Be aware that exposing UTF-8 metrics may reduce usability.
  • We intent to be able to unblock federation cases as follows:
# HELP metric1 some help
metric1{__type...=a}
metric1{__type...=b}

We don't know the exact solution, but we want to experiment.


Empty label values SHOULD be treated as if the label was not present.

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