> ## Documentation Index
> Fetch the complete documentation index at: https://docs.openlayer.com/llms.txt
> Use this file to discover all available pages before exploring further.

# 99th latency percentile

> Learn how to use the 99th latency percentile test

## Definition

The 99th latency percentile test ensures that the 99th percentile latency for the data is within a given range.

## Taxonomy

* **Task types**: LLM, tabular classification, tabular regression, text classification.
* **Availability**: monitoring (Monitor a model in production, measure its health, check for drifts and set up alerts.).

## Why it matters

* The 99th percentile latency captures the performance experienced by nearly all users, excluding only the worst 1% of cases.
* This metric helps identify performance issues that could affect even a small percentage of users, which is important for maintaining high service quality.
* Monitoring the 99th percentile is crucial for applications where consistent performance is critical, even for edge cases.

## Test configuration examples

If you are writing a `tests.json`, here are a few valid configurations for the 99th latency percentile test:

```json Development theme={null}
[
  {
    "name": "99th percentile latency below 12000 msec",
    "description": "Make sure that the 99th percentile latency is below 12000 msec",
    "type": "performance",
    "subtype": "metricThreshold",
    "thresholds": [
      {
        "insightName": "metrics",
        "measurement": "p99Latency",
        "operator": "<",
        "value": 12000
      }
    ],
    "subpopulationFilters": null,
    "mode": "development",
    "usesValidationDataset": true,
    "usesTrainingDataset": false,
    "usesMlModel": true,
    "syncId": "b4dee7dc-4f15-48ca-a282-63e2c04e0689"
  }
]
```

```json Monitoring theme={null}
[
  {
    "name": "99th percentile latency below 12000 msec",
    "description": "Make sure that the 99th percentile latency is below 12000 msec",
    "type": "performance",
    "subtype": "metricThreshold",
    "thresholds": [
      {
        "insightName": "metrics",
        "measurement": "p99Latency",
        "operator": "<",
        "value": 12000
      }
    ],
    "subpopulationFilters": null,
    "mode": "monitoring",
    "usesProductionData": true,
    "evaluationWindow": 3600,
    "delayWindow": 0,
    "syncId": "b4dee7dc-4f15-48ca-a282-63e2c04e0689"
  }
]
```

## Related

* [Mean latency test](https://docs.openlayer.com/tests/catalog/mean-latency.md).
* [Max latency test](https://docs.openlayer.com/tests/catalog/max-latency.md).
* [90th latency percentile test](https://docs.openlayer.com/tests/catalog/p90-latency.md).
* [95th latency percentile test](https://docs.openlayer.com/tests/catalog/p95-latency.md).


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