# Prompt libraries rot. Build evaluation sets instead.

Source: https://u-in.ai/blog/prompt-libraries-rot/
Updated: 2026-10-12

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- Prompt libraries rot. Build evaluation sets instead.

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PUBLISHED 20 SEPTEMBER 2026 · UPDATED 12 OCTOBER 2026 · 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.

[Olga Bialkovich · Founder · AI and marketing strategy](https://u-in.ai/authors/olga-bialkovich/)

Keep the test, not the prompt. PHOTO · U [IN] AI LAB

(IN THIS STORY)
- [01 — Why libraries rot](#01--why-libraries-rot)

- [02 — What to keep instead](#02--what-to-keep-instead)

1 MIN READ

## 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 Playbooks AI agents Quality

[Olga Bialkovich](https://u-in.ai/authors/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.

(WHO ANSWERS) Olga Bialkovich Founder · AI and marketing strategy
Reads every request and comes to the call with a first map of where agents would pay back in your funnel.

REPLIES WITHIN ONE WORKING DAY [Or book the call yourself](https://calendly.com/obelkovich/new-meeting)

(KEEP READING) [All stories](https://u-in.ai/blog/)

OPINION 09 OCT · 5 MIN

### U [in] AI founder Olga Bialkovich publishes new article on AI agent consistency in Unite.AI

Another conversation around U [in] AI has made its way into the international AI media space.

Olga Bialkovich

→ https://u-in.ai/blog/olga-bialkovich-unite-ai-ai-agent-consistency/

STRATEGY 29 SEPT · 1 MIN

### Why most AI pilots in marketing never reach production

Pilots are built to impress a steering committee, not to survive a Monday. What the fifth that ship do differently.

Olga Bialkovich

→ https://u-in.ai/blog/ai-pilots-never-reach-production/

CASE STUDY 24 SEPT · 1 MIN

### Three agents, one lead flow: the math behind −62%

We rebuilt qualification for an agri-tech distributor. Every number, every hand-off, every mistake on the way.

Katsiaryna Tsyrkina

→ https://u-in.ai/blog/three-agents-one-lead-flow/