# Semantic conventions for Node.js runtime metrics

**Status**: [Development][DocumentStatus]

This document describes semantic conventions for Node.js Runtime metrics in OpenTelemetry.


**Description:** In-development Node.js Runtime metrics captured under `nodejs`.

Note: The metrics for eventloop delay are split into separated values instead of a single histogram, because node runtime
only returns single values through [`perf_hooks.monitorEventLoopDelay([options])`][Eventloop] and not the entire
histogram, so it's not possible to convert it to an OpenTelemetry histogram.

## Metric: `nodejs.eventloop.delay.min`

This metric is [recommended][MetricRecommended].

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| Name | Instrument Type | Unit (UCUM) | Description | Stability | Entity Associations |
| -------- | --------------- | ----------- | -------------- | --------- | ------ |
| `nodejs.eventloop.delay.min` | Gauge | `s` | Event loop minimum delay. [1] | ![Development](https://img.shields.io/badge/-development-blue) | |

**[1]:** Value can be retrieved from value `histogram.min` of [`perf_hooks.monitorEventLoopDelay([options])`](https://nodejs.org/api/perf_hooks.html#perf_hooksmonitoreventloopdelayoptions)

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## Metric: `nodejs.eventloop.delay.max`

This metric is [recommended][MetricRecommended].

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| Name | Instrument Type | Unit (UCUM) | Description | Stability | Entity Associations |
| -------- | --------------- | ----------- | -------------- | --------- | ------ |
| `nodejs.eventloop.delay.max` | Gauge | `s` | Event loop maximum delay. [1] | ![Development](https://img.shields.io/badge/-development-blue) | |

**[1]:** Value can be retrieved from value `histogram.max` of [`perf_hooks.monitorEventLoopDelay([options])`](https://nodejs.org/api/perf_hooks.html#perf_hooksmonitoreventloopdelayoptions)

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## Metric: `nodejs.eventloop.delay.mean`

This metric is [recommended][MetricRecommended].

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| Name | Instrument Type | Unit (UCUM) | Description | Stability | Entity Associations |
| -------- | --------------- | ----------- | -------------- | --------- | ------ |
| `nodejs.eventloop.delay.mean` | Gauge | `s` | Event loop mean delay. [1] | ![Development](https://img.shields.io/badge/-development-blue) | |

**[1]:** Value can be retrieved from value `histogram.mean` of [`perf_hooks.monitorEventLoopDelay([options])`](https://nodejs.org/api/perf_hooks.html#perf_hooksmonitoreventloopdelayoptions)

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## Metric: `nodejs.eventloop.delay.stddev`

This metric is [recommended][MetricRecommended].

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| Name | Instrument Type | Unit (UCUM) | Description | Stability | Entity Associations |
| -------- | --------------- | ----------- | -------------- | --------- | ------ |
| `nodejs.eventloop.delay.stddev` | Gauge | `s` | Event loop standard deviation delay. [1] | ![Development](https://img.shields.io/badge/-development-blue) | |

**[1]:** Value can be retrieved from value `histogram.stddev` of [`perf_hooks.monitorEventLoopDelay([options])`](https://nodejs.org/api/perf_hooks.html#perf_hooksmonitoreventloopdelayoptions)

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## Metric: `nodejs.eventloop.delay.p50`

This metric is [recommended][MetricRecommended].

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| Name | Instrument Type | Unit (UCUM) | Description | Stability | Entity Associations |
| -------- | --------------- | ----------- | -------------- | --------- | ------ |
| `nodejs.eventloop.delay.p50` | Gauge | `s` | Event loop 50 percentile delay. [1] | ![Development](https://img.shields.io/badge/-development-blue) | |

**[1]:** Value can be retrieved from value `histogram.percentile(50)` of [`perf_hooks.monitorEventLoopDelay([options])`](https://nodejs.org/api/perf_hooks.html#perf_hooksmonitoreventloopdelayoptions)

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## Metric: `nodejs.eventloop.delay.p90`

This metric is [recommended][MetricRecommended].

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| Name | Instrument Type | Unit (UCUM) | Description | Stability | Entity Associations |
| -------- | --------------- | ----------- | -------------- | --------- | ------ |
| `nodejs.eventloop.delay.p90` | Gauge | `s` | Event loop 90 percentile delay. [1] | ![Development](https://img.shields.io/badge/-development-blue) | |

**[1]:** Value can be retrieved from value `histogram.percentile(90)` of [`perf_hooks.monitorEventLoopDelay([options])`](https://nodejs.org/api/perf_hooks.html#perf_hooksmonitoreventloopdelayoptions)

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## Metric: `nodejs.eventloop.delay.p99`

This metric is [recommended][MetricRecommended].

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| Name | Instrument Type | Unit (UCUM) | Description | Stability | Entity Associations |
| -------- | --------------- | ----------- | -------------- | --------- | ------ |
| `nodejs.eventloop.delay.p99` | Gauge | `s` | Event loop 99 percentile delay. [1] | ![Development](https://img.shields.io/badge/-development-blue) | |

**[1]:** Value can be retrieved from value `histogram.percentile(99)` of [`perf_hooks.monitorEventLoopDelay([options])`](https://nodejs.org/api/perf_hooks.html#perf_hooksmonitoreventloopdelayoptions)

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## Metric: `nodejs.eventloop.utilization`

This metric is [recommended][MetricRecommended].

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| Name | Instrument Type | Unit (UCUM) | Description | Stability | Entity Associations |
| -------- | --------------- | ----------- | -------------- | --------- | ------ |
| `nodejs.eventloop.utilization` | Gauge | `1` | Event loop utilization. [1] | ![Development](https://img.shields.io/badge/-development-blue) | |

**[1]:** The value range is [0.0, 1.0] and can be retrieved from [`performance.eventLoopUtilization([utilization1[, utilization2]])`](https://nodejs.org/api/perf_hooks.html#performanceeventlooputilizationutilization1-utilization2)

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## Metric: `nodejs.eventloop.time`

This metric is [recommended][MetricRecommended].

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| Name | Instrument Type | Unit (UCUM) | Description | Stability | Entity Associations |
| -------- | --------------- | ----------- | -------------- | --------- | ------ |
| `nodejs.eventloop.time` | Counter | `s` | Cumulative duration of time the event loop has been in each state. [1] | ![Development](https://img.shields.io/badge/-development-blue) | |

**[1]:** Value can be retrieved from [`performance.eventLoopUtilization([utilization1[, utilization2]])`](https://nodejs.org/api/perf_hooks.html#performanceeventlooputilizationutilization1-utilization2)

**Attributes:**

| Key | Stability | [Requirement Level](/docs/specs/semconv/general/attribute-requirement-level/) | Value Type | Description | Example Values |
| --- | --- | --- | --- | --- | --- |
| [`nodejs.eventloop.state`](/docs/specs/semconv/registry/attributes/nodejs.md) | ![Development](https://img.shields.io/badge/-development-blue) | `Required` | string | The state of event loop time. | `active`; `idle` |

---

`nodejs.eventloop.state` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

| Value | Description | Stability |
| --- | --- | --- |
| `active` | Active time. | ![Development](https://img.shields.io/badge/-development-blue) |
| `idle` | Idle time. | ![Development](https://img.shields.io/badge/-development-blue) |

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[DocumentStatus]: https://github.com/open-telemetry/opentelemetry-specification/blob/v1.54.0/specification/document-status.md
[MetricRecommended]: /docs/specs/semconv/general/metric-requirement-level.md#recommended
[Eventloop]: https://nodejs.org/api/perf_hooks.html#perf_hooksmonitoreventloopdelayoptions