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Naming

Status: Stable, Unless otherwise specified.

Table of Contents

General Naming Considerations

This section applies to attribute names (also known as the "attribute keys"), as well as Metric and Event names. For brevity within this section when we use the term "name" without an adjective it is implied to mean all of these.

Every name MUST be a valid Unicode sequence.

Note: we merely require that the names are represented as Unicode sequences. This specification does not define how exactly the Unicode sequences are encoded. The encoding can vary from one programming language to another and from one wire format to another. Use the idiomatic way to represent Unicode in the particular programming language or wire format.

Names SHOULD follow these rules:

  • Names SHOULD be lowercase.

  • Use namespacing. Delimit the namespaces using a dot character. For example service.version denotes the service version where service is the namespace and version is an attribute in that namespace.

  • Namespaces can be nested. For example telemetry.sdk is a namespace inside top-level telemetry namespace and telemetry.sdk.name is an attribute inside telemetry.sdk namespace.

    Use namespaces (and dot separator) whenever it makes sense. For example when introducing an attribute representing a property of some object, follow *{object}.{property} pattern. Avoid using underscore (*{object}_{property}) if this object could have other properties.

  • For each multi-word dot-delimited component of the name separate the words by underscores (i.e. use snake_case). For example http.response.status_code denotes the status code in the http namespace.

    Use underscore only when using dot (namespacing) does not make sense or changes the semantic meaning of the name. For example, use rate_limiting instead of rate.limiting.

  • Be precise. Attribute, event, metric, and other names should be descriptive and unambiguous.

    • When introducing a name describing a certain property of the object, include the property name. For example, use file.owner.name instead of file.owner and system.network.packet.dropped instead of system.network.dropped
    • Avoid introducing names and namespaces that would mean different things when used by different conventions or instrumentations. For example, use security_rule instead of rule.

  • Use shorter names when it does not compromise clarity. Drop namespace components or words in multi-word components when they are not necessary. For example, vcs.change.id describes pull request id as precisely as vcs.repository.change.id does.

Name Abbreviation Guidelines

Abbreviations MAY be used when they are widely recognized and commonly used.

Examples include common technical abbreviations such as IP, DB, CPU, HTTP, URL, or product names like AWS, GCP, K8s.

Abbreviations that are commonly recognized but only within a certain domain MAY be used when qualified by the corresponding namespace.

For example, use container.csi.* instead of container.container_storage_interface or container.oci.* instead of container.open_container_initiative.*

Abbreviations SHOULD be avoided if they are ambiguous, for example, when they apply to multiple products or concepts.

Name Reuse Prohibition

Two attributes, two metrics, or two events MUST NOT share the same name. Different entities (attribute and metric, metric and event) MAY share the same name.

Attributes, metrics, and events SHOULD NOT be removed from semantic conventions regardless of their maturity level. When the convention is renamed or no longer recommended, it SHOULD be deprecated.

Recommendations for OpenTelemetry Authors

  • When coming up with a new semantic convention make sure to check existing namespaces (Semantic Conventions) to see if a similar namespace already exists.

  • All names that are part of OpenTelemetry semantic conventions SHOULD be part of a namespace.

  • When a new namespace is necessary consider whether it should be a top-level namespace (e.g. service) or a nested namespace (e.g. service.instance).

  • Semantic conventions MUST limit names to printable Basic Latin characters (more precisely to U+0021 .. U+007E subset of Unicode code points). It is recommended to further limit names to the following Unicode code points: Latin alphabet, Numeric, Underscore, Dot (as namespace delimiter).

Note: Semantic Conventions tooling limits names to lowercase Latin alphabet, Numeric, Underscore, Dot (as namespace delimiter). Names must start with a letter, end with an alphanumeric character, and must not contain two or more consecutive delimiters (Underscore or Dot).

Recommendations for Application Developers

As an application developer when you need to record an attribute, metric, event, or other signal first consult existing semantic conventions. If an appropriate name does not exists you will need to come up with a new name. To do that consider a few options:

  • The name is specific to your company and may be possibly used outside the company as well. To avoid clashes with names introduced by other companies (in a distributed system that uses applications from multiple vendors) it is recommended to prefix the new name by your company's reverse domain name, e.g. com.acme.shopname.

  • The name is specific to your application that will be used internally only. If you already have an internal company process that helps you to ensure no name clashes happen then feel free to follow it. Otherwise it is recommended to prefix the attribute name by your application name, provided that the application name is reasonably unique within your organization (e.g. myuniquemapapp.longitude is likely fine). Make sure the application name does not clash with an existing semantic convention namespace.

  • It is not recommended to use existing OpenTelemetry semantic convention namespace as a prefix for a new company- or application-specific attribute name. Doing so may result in a name clash in the future, if OpenTelemetry decides to use that same name for a different purpose or if some other third party instrumentation decides to use that exact same attribute name and you combine that instrumentation with your own.

  • The name may be generally applicable to applications in the industry. In that case consider submitting a proposal to this specification to add a new name to the semantic conventions, and if necessary also to add a new namespace.

It is recommended to limit names to printable Basic Latin characters (more precisely to U+0021 .. U+007E subset of Unicode code points).

Attributes

otel.* Namespace

Attribute names that start with otel. are reserved to be defined by OpenTelemetry specification. These are typically used to express OpenTelemetry concepts in formats that don't have a corresponding concept.

For example, the otel.scope.name attribute is used to record the instrumentation scope name, which is an OpenTelemetry concept that is natively represented in OTLP, but does not have an equivalent in other telemetry formats and protocols.

Any additions to the otel.* namespace MUST be approved as part of OpenTelemetry specification.

Attribute Name Pluralization Guidelines

  • When an attribute represents a single entity, the attribute name SHOULD be singular. Examples: host.name, container.id.

  • When attribute can represent multiple entities, the attribute name SHOULD be pluralized and the value type SHOULD be an array. E.g. process.command_args might include multiple values: the executable name and command arguments.

  • When an attribute represents a measurement, Metric Name Pluralization Guidelines SHOULD be followed for the attribute name.

Signal-specific Attributes

Status: Experimental

Attributes are defined in semantic conventions in a signal-agnostic way. The same attribute is expected to be used on multiple signals.

When an attribute is defined, it is not always clear if it will be applicable outside of a certain metric, event, or other convention.

Attributes that are unlikely to have any usage beyond a specific convention, SHOULD be added under that metric (event, etc) namespace.

Examples:

Attributes mode and mountpoint for metric system.filesystem.usage should be namespaced as system.filesystem.mode and system.filesystem.mountpoint.

Metrics, events, resources, and other signals are expected and encouraged to use applicable attributes from multiple namespaces.

Examples:

Metric http.server.request.duration uses attributes from the registry such as server.port, error.type.

Metrics

Status: Experimental

Naming Rules for Counters and UpDownCounters

Pluralization

Metric namespaces SHOULD NOT be pluralized.

Metric names SHOULD NOT be pluralized, unless the value being recorded represents discrete instances of a countable quantity. Generally, the name SHOULD be pluralized only if the unit of the metric in question is a non-unit (like {fault} or {operation}).

Examples:

  • system.filesystem.utilization, http.server.request.duration, and system.cpu.time should not be pluralized, even if many data points are recorded.
  • system.paging.faults, system.disk.operations, and system.network.packets should be pluralized, even if only a single data point is recorded.

Use count Instead of Pluralization for UpDownCounters

If the value being recorded represents the count of concepts signified by the namespace then the metric should be named count (within its namespace).

For example if we have a namespace system.process which contains all metrics related to the processes then to represent the count of the processes we can have a metric named system.process.count.

Do Not Use total

UpDownCounters SHOULD NOT use _total because then they will look like monotonic sums.

Counters SHOULD NOT append _total either because then their meaning will be confusing in delta backends.

Instrument Naming

Status: Experimental

  • limit - an instrument that measures the constant, known total amount of something should be called entity.limit. For example, system.memory.limit for the total amount of memory on a system.

  • usage - an instrument that measures an amount used out of a known total (limit) amount should be called entity.usage. For example, system.memory.usage with attribute state = used | cached | free | ... for the amount of memory in a each state. Where appropriate, the sum of usage over all attribute values SHOULD be equal to the limit.

    A measure of the amount consumed of an unlimited resource, or of a resource whose limit is unknowable, is differentiated from usage. For example, the maximum possible amount of virtual memory that a process may consume may fluctuate over time and is not typically known.

  • utilization - an instrument that measures the fraction of usage out of its limit should be called entity.utilization. For example, system.memory.utilization for the fraction of memory in use. Utilization can be with respect to a fixed limit or a soft limit. Utilization values are represented as a ratio and are typically in the range [0, 1], but may go above 1 in case of exceeding a soft limit.

  • time - an instrument that measures passage of time should be called entity.time. For example, system.cpu.time with attribute state = idle | user | system | .... time measurements are not necessarily wall time and can be less than or greater than the real wall time between measurements.

    time instruments are a special case of usage metrics, where the limit can usually be calculated as the sum of time over all attribute values. utilization for time instruments can be derived automatically using metric event timestamps. For example, system.cpu.utilization is defined as the difference in system.cpu.time measurements divided by the elapsed time and number of CPUs.

  • io - an instrument that measures bidirectional data flow should be called entity.io and have attributes for direction. For example, system.network.io.

  • Other instruments that do not fit the above descriptions may be named more freely. For example, system.paging.faults and system.network.packets. Units do not need to be specified in the names since they are included during instrument creation, but can be added if there is ambiguity.