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Binate AI
Generative AI · February 12, 2026

How to Evaluate LLM Applications: Building an Eval Harness

You cannot improve what you cannot measure. Here is how to build an evaluation harness that tells you if your LLM app is getting better or worse.

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Binate AI

February 12, 2026

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01What is an LLM eval harness?

An eval harness is an automated test suite for an AI system: a fixed set of representative inputs, expected behaviors, and scoring functions that run on every change. It turns "it feels better" into a number you can defend.

02Build a golden dataset first

Collect 50–200 real, hard cases — the edge cases, the ambiguous queries, the ones that broke before. This golden set is your regression net. Without it, every prompt tweak is a gamble.

Action Checklist

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Golden set checklist

03Score with rules first, judges second

Use deterministic checks where possible (exact match, schema valid, contains citation). For open-ended quality, use an LLM-as-judge with a clear rubric — but calibrate the judge against human ratings before trusting it.

04Test yourself

The foundation of evaluation is not the scorer.

Quick Quiz

What should you build first when evaluating an LLM app?

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The takeaway

Golden set, deterministic checks, a calibrated judge, and CI integration: that is an eval harness that keeps quality climbing.

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