Every classifier and every LLM-as-judge eval reduces to a confusion matrix, but the screen is whether you handle the zero-denominator cases without crashing and can say which metric matters for the problem at hand.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
Every classifier and every LLM-as-judge eval reduces to a confusion matrix, but the screen is whether you handle the zero-denominator cases without crashing and can say which metric matters for the problem at hand.
The discriminators are the degenerate denominators. A model that predicts nothing positive has undefined precision (no positives to be right about); one where the dataset has no positives has undefined recall. Candidates who divide by zero and crash, or who silently return 1.0 without saying why, miss the signal. The deeper probe is whether they can pick precision over recall for a given cost asymmetry, which is the real FDE judgment call.
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