INVEST
Acronyminvest criteria, invest user story criteriaDefinition
Bill Wake's six tests of a good user story — Independent, Negotiable, Valuable, Estimable, Small, Testable: it can be built in any order, its details are a conversation rather than a contract, it delivers something a user would notice, the team can size it, it fits in a sprint, and there is a way to know it is done
A checklist for backlog refinement, and a diagnosis when a story is stuck: not estimable usually means not understood, not small usually means an epic in disguise, not testable means the acceptance criteria were never written — which is where Gherkin's Given / When / Then comes in. Valuable is the one teams skip: a story that only a developer would notice is a task, and belongs under a story that is not.
Six adjectives, one question each, asked before a story is pulled. The value is in the ones that fail: a story that misses a letter is telling the team what to do to it — split it, talk about it, write the test — before anyone starts.