Glossary · definition-drift
GLOSSARY
Definition drift
What happens when the same formula or reference table is copied into several scripts and updated in only some of them. The stale copy keeps reporting correctly from the wrong facts, which is exactly why it survives review. One stored definition is executed directly, or re-derived by a check that fails naming the key.
Principle 10 · A metric without its definition is not a number
Where does Definition drift come from?
Principle 10 of the Kymira doctrine, A metric without its definition is not a number. Definition drift is the name the doctrine gives to what that principle requires in practice.
What failure is Definition drift named after?
The definition that drifted between copies. The same reference table pasted into three scripts, updated in two. The stale copy keeps reporting, correctly, from the wrong facts.
What does it look like on a real file?
The same churn formula lives in three scripts, two were updated, and the third keeps reporting correctly from stale facts.
Not for
Not caught by testing each script. Every copy passes its own tests; the drift shows only when the copies are compared.
Nearest terms
Last updated 2026-09-02 · Dylan, founder · one of 40 terms in the Kymira glossary, each one named after something we watched go wrong in a real build or in our own audits.