

Free Lesson
Build an Eval Harness from Scratch
30 min
Nov 2, 2026 9:00 AM
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What you'll learn
Structure a dataset, runner and scorer
Build all three from an empty file to a passing run in one sitting.
Add a regression check on every change
Wire the harness in so quality drops get caught before they ship.
Keep it fast enough that people run it
Make design choices that stop the suite becoming something everyone skips.
Why this topic matters
Everyone agrees you should have evals. Far fewer people have opened one and seen what it consists of. Stripped of frameworks it is three things: a dataset, a runner and a scorer. Building it by hand once makes every eval tool afterwards make sense and makes it obvious when you do not need one.






