# What is Tessary's tool_error classifier?

tool_error is one of Tessary's built-in classifiers: it watches the rate at which a tool's calls fail, not any single call. A call counts as failed only on structural evidence, an error status on the span, a recorded exception, or a result that declares itself an error, never on output text that merely mentions the word `error`.

Each tool gets its own alert threshold, set from that tool's own normal failure rate and a false-alarm budget, rather than one fixed cutoff shared across every tool. That way a chatty, error-prone integration and a normally reliable API aren't judged against the same bar. Evidence accumulates call by call, so a tool failing at its usual rate stays quiet, and only a sustained shift fires.

A detection is one finding per tool: when the rate moved, which failure patterns drove it, and which call sites the traffic came through. Triage confirms a real deviation before it becomes a case anyone has to act on.

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Source: https://tessary.ai/answers/tessary-tool-error/what-is-tessarys-tool-error-classifier
More on Tessary tool error: https://tessary.ai/answers/tessary-tool-error
From Tessary, agent reliability for AI agents in production: https://tessary.ai