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Dev.to
Dev.to
7/8/2026
The original title is "How to Build an Evaluation Harness for Your AI Agent (So It Doesn't Break in Production)"

The original title is "How to Build an Evaluation Harness for Your AI Agent (So It Doesn't Break in Production)"

Original: How to Build an Evaluation Harness for Your AI Agent (So It Doesn't Break in Production)

Short summary

This tutorial walks through building a Python-based evaluation harness for AI agents using four graders: Truth (correct tool calls), Path (sane trajectory), Judge (LLM-as-judge for fuzzy outcomes), and Gate (CI regression detection). It explains why manual testing fails for agents—demo bias, non-determinism, and silent regressions—and provides a starter dataset pattern sourced from real failures. The approach is framework-agnostic and integrates into CI to catch regressions before users do.

  • Four graders: Truth, Path, Judge, and Gate cover tool-call correctness, trajectory sanity, outcome quality, and CI regression
  • Start with 20-50 tasks drawn from real failures with unambiguous pass/fail criteria
  • Framework-agnostic pattern works with LangChain, LangGraph, MCP, or custom agent setups

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