A manual QA script is written for a reader who fills gaps. "Log in and check the dashboard looks right" assumes the tester knows which account, which browser, which data, and what "right" means. An agent has none of that shared context. When you hand it a vague instruction, it will produce something that technically matches what you wrote and misses what you meant, which is the failure the JetBrains guide to spec-driven coding warns about when it says agents are most effective when given clear structure and guidance rather than vague instructions like "refactor this module" 1.
The second problem is trust. A coding agent's final message can say "done" when nothing has checked the final code at all. One developer audited 516 such claims from his own sessions and found no passing test run behind 65 to 69% of them, depending on how strictly they were counted 12. If you accept a prose checklist as the contract, you are accepting unverified self-reports as your quality record.
The third problem is scope. A checklist item that mixes five assertions ("the form submits, the email arrives, the record appears in the database, the confirmation renders, and the audit log updates") cannot be scored pass or fail honestly, because a partial pass still reads as a fail and hides which part broke. The fix is the same one that makes user stories work: slice vertically into pieces that each have independently measurable value, rather than horizontally into technical layers that only make sense to one specialist 8. In testing terms, each check should cross the whole path of one behavior and report its own verdict.
There is a wider argument for doing this as a written artifact rather than a chat instruction. Quality has to be embedded through gates that an agent cannot bypass, because agents produce plausible-looking code that passes superficial inspection but drifts from requirements, and a framework of enforced gates makes shipping bad work harder than shipping good work 11. The checklist conversion is the smallest useful version of that framing.



