> For the complete documentation index, see [llms.txt](https://docs.zenml.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.zenml.io/kitaru/core-concepts.md).

# Core Concepts

- [Overview](https://docs.zenml.io/kitaru/core-concepts/concepts.md): A handful of nouns and one verb, and how sessions, replays, evaluators, cohorts, experiments, investigations, and workers fit together.
- [Agents & Sessions](https://docs.zenml.io/kitaru/core-concepts/agents-and-sessions.md): The agent is the identity, the session is the recording of every model call, tool call, and decision a run left behind.
- [Investigations & Annotations](https://docs.zenml.io/kitaru/core-concepts/investigations.md): Where your judgment enters the system: your coding assistant maps the evidence, interviews you in context, and pins your answers to exact trace evidence as annotations.
- [Replay](https://docs.zenml.io/kitaru/core-concepts/replay.md): Re-run a recorded session against your real code, unchanged for a faithful baseline or forked with one thing different.
- [Evaluators & Evaluations](https://docs.zenml.io/kitaru/core-concepts/evaluators.md): Evaluators turn sessions into evaluations: the rows they write. Numbers average, words count, free text gets read.
- [Analyzers & Insights](https://docs.zenml.io/kitaru/core-concepts/analyzers.md): Analyzers turn many sessions into insights: the aggregate read a single evaluator can't give you.
- [Cohorts](https://docs.zenml.io/kitaru/core-concepts/cohorts.md): Named, versioned sets of sessions; the population an experiment replays, frozen so results stay comparable.
- [Experiments](https://docs.zenml.io/kitaru/core-concepts/experiments.md): A named change, replayed across a cohort and evaluated. What improved, what regressed, before you ship.
- [Workers](https://docs.zenml.io/kitaru/core-concepts/workers.md): The process that runs replays, imports, and evaluators as subprocesses in your environment, so your code and data never leave your systems.
- [Under the Hood](https://docs.zenml.io/kitaru/core-concepts/under-the-hood.md): The machinery behind the loop: a FastAPI server on Postgres, workers claiming tasks, and where Kitaru sits beside your observability stack.


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