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# Semantic conventions for Node.js runtime metrics

**Status**: [Experimental][DocumentStatus]

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

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- [Experimental](#experimental)
  - [Metric: `nodejs.eventloop.delay.min`](#metric-nodejseventloopdelaymin)
  - [Metric: `nodejs.eventloop.delay.max`](#metric-nodejseventloopdelaymax)
  - [Metric: `nodejs.eventloop.delay.mean`](#metric-nodejseventloopdelaymean)
  - [Metric: `nodejs.eventloop.delay.stddev`](#metric-nodejseventloopdelaystddev)
  - [Metric: `nodejs.eventloop.delay.p50`](#metric-nodejseventloopdelayp50)
  - [Metric: `nodejs.eventloop.delay.p90`](#metric-nodejseventloopdelayp90)
  - [Metric: `nodejs.eventloop.delay.p99`](#metric-nodejseventloopdelayp99)
  - [Metric: `nodejs.eventloop.utilization`](#metric-nodejseventlooputilization)
  - [Metric: `nodejs.eventloop.time`](#metric-nodejseventlooptime)

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## Experimental

**Status**: [Experimental][DocumentStatus]

**Description:** Experimental 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 |
| -------- | --------------- | ----------- | -------------- | --------- |
| `nodejs.eventloop.delay.min` | Gauge | `s` | Event loop minimum delay. [1] | ![Experimental](https://img.shields.io/badge/-experimental-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 |
| -------- | --------------- | ----------- | -------------- | --------- |
| `nodejs.eventloop.delay.max` | Gauge | `s` | Event loop maximum delay. [1] | ![Experimental](https://img.shields.io/badge/-experimental-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 |
| -------- | --------------- | ----------- | -------------- | --------- |
| `nodejs.eventloop.delay.mean` | Gauge | `s` | Event loop mean delay. [1] | ![Experimental](https://img.shields.io/badge/-experimental-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 |
| -------- | --------------- | ----------- | -------------- | --------- |
| `nodejs.eventloop.delay.stddev` | Gauge | `s` | Event loop standard deviation delay. [1] | ![Experimental](https://img.shields.io/badge/-experimental-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 |
| -------- | --------------- | ----------- | -------------- | --------- |
| `nodejs.eventloop.delay.p50` | Gauge | `s` | Event loop 50 percentile delay. [1] | ![Experimental](https://img.shields.io/badge/-experimental-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 |
| -------- | --------------- | ----------- | -------------- | --------- |
| `nodejs.eventloop.delay.p90` | Gauge | `s` | Event loop 90 percentile delay. [1] | ![Experimental](https://img.shields.io/badge/-experimental-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 |
| -------- | --------------- | ----------- | -------------- | --------- |
| `nodejs.eventloop.delay.p99` | Gauge | `s` | Event loop 99 percentile delay. [1] | ![Experimental](https://img.shields.io/badge/-experimental-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 |
| -------- | --------------- | ----------- | -------------- | --------- |
| `nodejs.eventloop.utilization` | Gauge | `1` | Event loop utilization. [1] | ![Experimental](https://img.shields.io/badge/-experimental-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 |
| -------- | --------------- | ----------- | -------------- | --------- |
| `nodejs.eventloop.time` | Counter | `s` | Cumulative duration of time the event loop has been in each state. [1] | ![Experimental](https://img.shields.io/badge/-experimental-blue) |

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

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

---

`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. | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
| `idle` | Idle time. | ![Experimental](https://img.shields.io/badge/-experimental-blue) |

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[DocumentStatus]: https://github.com/open-telemetry/opentelemetry-specification/tree/v1.41.0/specification/document-status.md
[MetricRecommended]: /docs/general/metric-requirement-level.md#recommended
[Eventloop]: https://nodejs.org/api/perf_hooks.html#perf_hooksmonitoreventloopdelayoptions
