# Tessary behavior drift

behavior_drift is one of Tessary's built-in classifiers. It learns how an agent normally behaves
from its own history, the steps it takes and the order it takes them in, and flags traces that
depart from that. It doesn't judge whether any answer was correct.

It catches the changes correctness checks miss: an agent that starts skipping a step it always ran,
calling tools it never used, or taking paths it has never taken. The baseline is fitted per call
site from its own traffic, so a new project is quiet by design until normal is established. New
patterns graduate into normal only after recurring across many sessions. Firings are grouped by
cause and triaged, and a confirmed finding opens a case.

## Questions answered under this concept

- [Does a behavior drift baseline go stale if an agent goes quiet?](https://tessary.ai/answers/tessary-behavior-drift/does-a-behavior-drift-baseline-go-stale-when-idle)
- [What does a behavior drift baseline catch, and what does it miss?](https://tessary.ai/answers/tessary-behavior-drift/what-does-a-behavior-drift-baseline-catch-and-miss)
- [Why did my agent stop doing a step it always used to do?](https://tessary.ai/answers/tessary-behavior-drift/why-did-my-agent-stop-doing-a-step-it-always-used-to-do)
- [Why doesn't one strange trace trigger a behavior drift alert?](https://tessary.ai/answers/tessary-behavior-drift/why-doesnt-one-strange-trace-trigger-a-behavior-drift-alert)
- [Why is my agent taking an action it never took before?](https://tessary.ai/answers/tessary-behavior-drift/why-is-my-agent-taking-an-action-it-never-took-before)

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Source: https://tessary.ai/answers/tessary-behavior-drift
All concepts: https://tessary.ai/answers
From Tessary, agent reliability for AI agents in production: https://tessary.ai