docs(evaluation): Usage & analytics

src/pages/docs/evaluation/guides/explore-playground/usage-analytics.mdx

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+---
+title: "Usage & analytics"
+description: "See how an eval has performed over time, and dig into any single run"
+---
+
+The **Usage** tab on an eval's page shows how the eval has performed over time, and lets you open any single run. A summary and chart sit at the top, and the full evaluation log runs below.
+
+## Open the eval
+
+From the **Evaluations** list, open the eval you want to inspect and switch to its **Usage** tab.
+
+<img src="/images/docs/evaluation/explore-playground/test-an-eval/select-eval.png" alt="The Evaluations list, searched for hallucination, with a prompt to select the eval you want to open" style={{ borderRadius: '5px' }} />
+*From the Evaluations list, open an eval to reach its Usage tab*
+
+## Pick a time range
+
+A row of ranges at the top scopes everything below it: **30 mins**, **6 hrs**, **Today**, **Yesterday**, **7D**, **30D**, **3M**, **6M**, and **12M**, or **Custom** for your own dates. Narrow it to a spike you are investigating, or widen it to watch the long trend.
+
+<img src="/images/docs/evaluation/explore-playground/usage-analytics/usage-tab.png" alt="The eval's Usage tab with a time-range selector, summary stats, a volume and completion-rate chart, and searchable evaluation logs below" style={{ borderRadius: '5px' }} />
+*The Usage tab: pick a time range, read the summary and chart, then dig into any run in the evaluation logs*
+
+## The summary and chart
+
+For the chosen range you get the headline numbers, **Runs**, **Success**, **Errors**, and **Task Completion Rate**, alongside a chart that plots **Volume**, how many runs, against the **Task Completion Rate** over time. A rate that dips or a volume that drops is your cue to look closer.
+
+## Evaluation logs
+
+Below the chart, **Evaluation Logs** lists every run the eval scored, one row each: its **Score** and **Result** (passed or failed), the **Input** it saw, the **Reason** for the verdict, the **Source** it ran under (**Playground**, **Dataset**, or **Tracer**, or the name of the project), and when it **Ran**. Use the **Search** box to find a run by a free-text match across its id, input, result, and reason.
+
+## Dive deeper
+
+<CardGroup cols={2}>
+  <Card title="Built-in evals" icon="tags" href="/docs/evaluation/builtin">
+    The library of evals you can browse and open
+  </Card>
+  <Card title="Running evaluations" icon="play" href="/docs/evaluation/guides/running-evaluations">
+    Attach an eval to your data so it starts recording usage
+  </Card>
+</CardGroup>