vertical-slice

Vertical slices decompose feature work into end-to-end user-visible capabilities, spanning mock APIs, frontend, and real database layers. This approach enables incremental delivery and faster feedback by avoiding horizontal layering that hides dependencies until late in the process.

You plan multi-stage UI and database changes by organizing each user-visible capability into a single slice containing a mock API, frontend component, real database update, and tests. Each slice ends with a checkpoint and model annotation to guide implementation.

You should prefer horizontal layering over vertical slices when end-to-end feature decomposition is impractical or obscures dependency resolution. The Skill provides specific guidance on avoiding anti-patterns and identifying scenarios where horizontal layering is the better architectural choice.

Model annotations use a tag (Model: sonnet|opus) to guide implementation and planning for each slice. Checkpoints mark the end of a slice, ensuring all steps—mock API, frontend, real database, and tests—are completed before progressing to the next incremental delivery phase.