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Builds multi-layer features as vertical end-to-end slices instead of horizontal layers. Each slice is verified before the next begins. Use when: starting any task that spans 2+ layers (DB, API, UI, tests), building CRUD features, implementing multi-step flows, decomposing features into subtasks, or planning implementation order.
npx skill4agent add oakoss/agent-skills tracer-bullets| Principle | Practice |
|---|---|
| Vertical over horizontal | Build one slice through all layers, not one layer across all features |
| Verify before advancing | Tests pass, page renders, round-trip works before next slice |
| One slice per session | Each slice should be completable in a single agent session |
| First feature sets pattern | First CRUD establishes conventions; subsequent CRUDs go faster |
| Check before building | Task trackers may already decompose the work into slices |
| Skip when trivial | Single-layer work or proven patterns don't need this ceremony |
| Slice | Scope | Verifies |
|---|---|---|
| 1 | Backend/API + tests (no UI) | Data layer works, conventions set, tests prove it |
| 2 | List page with real data | Data flows DB -> server -> rendered page |
| 3 | Create dialog | Full round-trip: form -> server -> DB -> refresh |
| 4 | Edit + delete | Full CRUD cycle, mutation patterns, confirm dialog |
| 5 | E2E test | Locks in the whole feature |
| Mistake | Correct Pattern |
|---|---|
| Building all API endpoints before any UI | Build one endpoint + its UI + its test, then the next |
| Starting UI before the backend is tested | Slice 1 is backend-only with tests; prove the data layer first |
| Building the full create/edit/delete UI in one pass | Create dialog first (slice 3), then edit + delete (slice 4) |
| Skipping verification between slices | Run tests and check output before starting the next slice |
| Making slices too large for one session | Split further; a slice that can't finish in one session is too big |
| Applying tracer bullets to trivial single-layer work | Skip for one component, one utility, or patterns already proven |