THE JOURNAL PLAYBOOK · 20 SEPTEMBER 2026
1 MIN READ
(PLAYBOOK) PUBLISHED · UPDATED · 1 MIN READ · PLAYBOOKS

Prompt libraries rot. Build evaluation sets instead.

A prompt that worked last quarter is a liability this one. What to keep instead, and how to know when the output has drifted.

An evaluation set being used to check AI output quality
Keep the test, not the prompt. PHOTO · U [IN] AI LAB

01 — Why libraries rot

Models change, offers change, and the person who wrote the prompt has left. What survives is not the instruction but the example of a good answer.

02 — What to keep instead

Twenty cases with the output you would accept, and the rule that decides pass or fail. When the model or the offer changes, you re-run them and see the damage in an hour.

FILED UNDER PlaybooksAI agentsQuality
Olga Bialkovich Founder · AI and marketing strategy Olga founded the lead-generation product that now runs as U [in] AI, and she sets the direction of the lab: which parts of marketing are worth automating, and which stay with people. Her working claim is a practical one — a system built around the right profile and the right message takes up to 60% out of the cost of finding customers and partners.
03 — YOUR TURN

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