Design feature

Design Feature

Product definition — the stage that turns an idea or a feature request into an exhaustive, checkable set of acceptance criteria, before any engineering planning happens. Docs only — no code, no branch.

Turn contract — verify before ending the turn

✓ The Product half of the SPEC is filled (Context, Business goals, Scope,
  Capability closure, Expectation sweep, Tooling, Product decisions, Deferred
  decisions) OR a `NEEDS_INPUT` question is pending — never a half-filled
  section left silently incomplete
✓ Every Capability closure row resolves to a filled surface (UI + API + test)
  or an explicit `n/a: <reason>` — a blank row is not a valid end state
✓ Integration closure walked the capability inventory (`docs/CAPABILITIES.md`,
  or the derived inventory when the project has none) with one resolved row
  per subsystem — zero subsystems skipped; every capability's role matrix
  lists EVERY inventory role as `allowed`/`denied`
✓ The Expectation sweep table is present and fully resolved (≥ 10 rows M/L,
  ≥ 5 XS/S; each `in-scope`/`out-of-scope`/`deferred` with a pointer) — an
  enumerated expectation left unresolved is not a valid end state
✓ Interview questions (when any were needed) went out ONE per turn — never a
  batched round
✓ `## Design status` is set to `designed` only when the Spec-lint product
  boxes all tick (closure complete included) — otherwise it stays
  `not designed` and the turn reports the failed boxes
✓ The roadmap row's status is set to `defined` in lockstep with `designed`
  (added at `idea` first if it didn't exist) — never `defined` with an
  incomplete closure, never `designed` with the roadmap row left at `idea`
✓ Upsert discipline honored: an existing SPEC/decisions.md was re-read first;
  nothing recorded there was destroyed; revisions were appended, not overwritten
✓ Artifact language: explicit user instruction > the project's declared docs
  language > English. The CONVERSATION language never decides — a Spanish
  prompt still produces an English SPEC/decisions unless one of the first two
  says otherwise
✓ The closing `→ Next:` block is printed as the ABSOLUTE last output

About to end the turn with any box unchecked? The turn is NOT done — complete the missing box first (weak models drop end-of-document duties; this list is first on purpose).

When to use

• A rough idea, no issue yet, and no SPEC: design-feature "<idea>".
• An existing feature slug whose SPEC is not yet marked designed: design-feature <NN-slug>.
• Revising an already-designed feature's product definition: design-feature <NN-slug> "<change>" (instruction mode), or bare design-feature <NN-slug> for review mode (see Interaction & upsert).
• plan-feature redirects here automatically when it detects an undesigned feature — you don't have to notice the gap yourself.

Step 0 — Discover the project (always first)

Per the agent guide's Workflow conventions + documentation map, then read what THIS skill needs: docs/features/_TEMPLATE/SPEC.md (the two-halves layout + ## Design status marker), the roadmap (docs/features/ROADMAP.md), the capability inventory (docs/CAPABILITIES.md — the substrate the Integration closure walks; if the project has none, derive an ad-hoc inventory from the architecture doc + codebase during step 5 and offer to seed the file from the template), and — if the slug already has a folder — its existing SPEC.md and decisions.md in full (upsert never starts blind). Skim the architecture doc and domain/style docs relevant to the idea's area only far enough to ground capability closure in the project's real entities and roles — deep engineering research is the Engineering half's job, not this one.

Process

1. Resolve the slug. A raw idea with no existing folder → propose a number (next free roadmap slot) and a kebab-case slug; confirm before writing. An existing NN-slug → that folder's SPEC.md (create the folder + copy the template if the roadmap has the row but no folder yet).

2. Interaction rule (fixed — no interpretation):

   • Bare design-feature <slug> (existing SPEC/decisions found): print a summary of what the feature currently does (or would do, from a fresh idea) → ask what to add / remove / change. This doubles as review mode.
   • design-feature <slug> <instruction>: apply the instruction directly, no questions — touch only what the instruction implies. Still re-reads the existing SPEC/decisions first (upsert, never blind).
   • Nothing exists yet (brand-new idea, no prior SPEC): go straight to step 3 (interview), since there is nothing to review or upsert.

3. Raw-idea interview (folded in, only when starting from zero or the instruction leaves genuine gaps). Fixed protocol — structural, not judgement:

   • One question per turn, never batched. Each question carries a recommended default the user can accept with one word. Ask nothing the docs or the instruction already answer.
   • Vagueness rubric (fixed slots — the question list IS this list). Probe each slot until it is filled or explicitly n/a: <reason>:
     1. Affected users/roles — who uses it; who must not.
     2. Error & edge states — what happens on failure / empty / invalid.
     3. Data shape — what is stored and shown, roughly.
     4. Boundaries & limits — sizes, counts, rates, thresholds.
     5. Out of scope — what this deliberately does NOT do.
     6. Success criteria — how we verify it worked.
   • Mandatory-question rule. A stated requirement that has no verifiable acceptance criterion yet is automatically the next question — no requirement enters the SPEC without one.
   • Reframe, don't interrogate. Restate each vague requirement as measurable criteria ("fast" → "list renders < 200 ms at 1k rows") and ask: "are these the right targets?" — a yes converts directly into acceptance criteria.
   • Deferred decisions. An answer of "decide later" is recorded as a row in the SPEC's ### Deferred decisions (with a decide-by trigger) — never dropped, never silently guessed.
   • Escalation (structural). If, after the interview, ≥ 3 rubric slots remain empty (neither filled nor n/a), do not guess: end the turn NEEDS_INPUT, listing the empty slots verbatim as the pending questions — the feature is not designable yet.
   • The identity questions ride the same one-per-turn protocol: problem & goal, business goals, size estimate (XS/S/M/L — XS/S stays SPEC-only, M/L gets the full artifact set), non-goals / future work, traceability (offer a tracking issue; if created, the eventual PR will Closes #n).

4. Proportional research. Capability closure (step 5) is cheap and comes first. Reach for external or domain research only when the feature touches a domain genuinely new to the project (a regulation, an unfamiliar integration, an industry convention with no precedent in the codebase) — never as a systematic per-feature step.

5. Capability closure (the core). Walk the SPEC template's three fixed checklists (docs/features/_TEMPLATE/SPEC.md → ### Capability closure is the authoritative block — instantiate it, never paraphrase it) and write the result into the SPEC's ### Capability closure section. Every row resolves to a filled surface or an explicit n/a: <reason> — a blank row is not a valid state, it is an unfinished design:

   1. Entity closure — for every entity the feature introduces or touches: Create/Read/Update/Delete/state-transitions, each with UI entry point + API surface + test.
   2. Integration closure — reconcile the feature against every subsystem in the capability inventory (docs/CAPABILITIES.md), one row per subsystem, none skipped: how does this feature touch auth, ACL, navigation, notifications, search, audit, settings, …? ("blog" ⇒ ACL gets a blog:write permission; the dashboard gets an "Articles" link with drafts above published and a "New article" button; auth is required to write.) No inventory file → derive the inventory from the architecture doc + codebase, record it in the section, walk it, and offer to seed docs/CAPABILITIES.md from the template (upsert-safe, user confirms).
   3. Role matrix — for every capability, EVERY role in the inventory is explicitly allowed or denied — no role unlisted, no "admins obviously can" left implicit.

   The filled rows become the Acceptance criteria — copy each resolved row (or its n/a line) into ## Acceptance criteria as an objective, checkable condition. Do not restate them loosely; the checklist row is the criterion.

6. Expectation sweep (the implicit-knowledge gate). Enumerate ≥ 10 candidate expectations (M/L; ≥ 5 for XS/S) a competent human would assume ship with a feature of this kind without being told — domain conventions, not project specifics ("a blog has drafts and a publish action", "a list has an empty state", "a delete asks for confirmation"). Fill the SPEC's ### Expectation sweep table: each row resolves to exactly one of in-scope (add/point to an acceptance criterion), out-of-scope (add to Out of scope / non-goals), or deferred (row in Deferred decisions) — never left unmentioned. Rows the user rejects are recorded as out-of-scope, not dropped: a rejected expectation is a future surprise defused. When a resolution genuinely needs the user's call, it rides the step-3 interview protocol (one question per turn, recommended default).

7. Scale-down for XS features. The gate stays uniform — every closure row and inventory subsystem is still walked, the sweep still runs (≥ 5 rows) — but for a small feature most rows resolve to n/a: out of scope for this slice in one pass, and the interview (step 3) may be a single confirming question. Passing the gate is cheap; the gate itself never opens.

8. Per-feature tooling notes. Check which installed skills/MCPs are relevant to this feature (e.g. a payments MCP for a billing feature) and record them in ## Tooling. This is not a global discovery sweep — that is product-audit's job; record only what this feature will actually use.

9. Write the Product half. Fill Context, Business goals, Scope (in/out), Capability closure, Acceptance criteria, Tooling, Product decisions, and Deferred decisions (none if empty) in the SPEC. When instantiating the closure, replace the template's fenced example block with the filled rows (keeping it fails the spec-lint's placeholder box). Record every non-obvious call in Product decisions with its rationale, and log any residual unknown as an open question in decisions.md rather than guessing.

10. Run the Spec-lint product boxes, then stamp. Mechanically check the SPEC template's ### Spec-lint product boxes (docs/features/_TEMPLATE/SPEC.md) and paste the box results. All product boxes tick → set the marker to designed and set this feature's docs/features/ROADMAP.md row status to defined (the idea → defined transition this skill owns — see the roadmap's Status legend). If the row doesn't exist yet (brand-new feature, no prior idea row), add it first at idea (number, slug, dependencies), then promote it to defined in the same edit — no feature is ever registered directly at defined without passing through idea. Any spec-lint product box FAILing (a blank closure row, an unlabelled prose criterion, an in-scope item with no criterion, …), or an unresolved question blocking closure → leave ## Design status at not designed, leave the roadmap row at idea (or unadded), and end the turn with the failed boxes / pending question stated plainly instead of a false designed stamp or a premature defined write.

11. Confirm the roadmap row. The row from step 11 carries the right number, slug, dependencies, and status (defined). Beyond defined, status transitions (planned, in-progress, done) are plan-feature-scaffold's and execute-phase's job — this skill never writes past defined.

12. Upsert semantics (never destroy). Re-running on an existing slug re-reads the SPEC and decisions.md first; a revision appends to decisions.md (dated, with what changed and why) — it never rewrites or deletes a prior decision. The only path that starts the product half from zero is an explicit "delete and redesign" in the prompt; even then, record that reset itself in decisions.md. This is the retrofit path audit-pr's closure-integrity gate routes to: a legacy SPEC with no Capability closure block trips that gate's dated design-debt: closure absent, SPEC predates the rule warning (never a blocker) on the next PR touching the feature; re-running design-feature <slug> there fills only the missing closure rows via this same upsert — it never rewrites what's already recorded.

13. Hand off. Once designed, print the closing block (see Done when) recommending /plan-feature <slug>.

Guardrails

• Docs only — no code, no branch (that is execute-phase), no engineering content (architecture, design, phases, testing — that is plan-feature's Engineering half; do not pre-fill it here even if the answer seems obvious).
• Never stamp ## Design status: designed with a blank Capability closure row, a skipped inventory subsystem, an incomplete role matrix, or an unresolved Expectation sweep row — a skipped row silently un-does the entire point of this skill.
• The Expectation sweep enumerates domain conventions, not new scope: it may only route each expectation to in-scope / out-of-scope / deferred — it never silently grows the feature beyond what the user confirms.
• No systematic per-feature market research; no global skill/MCP discovery sweep (product-audit's job); no --update flag — upsert is always the default behavior, not an opt-in.
• Don't build a separate DESIGN.md — one SPEC, two halves, always.
• Composition tier. This skill is planning-class (judgment work — run it on your strongest model / highest effort). plan-feature-from-issue composing this skill in-turn for a thin issue is allowed only when it runs at ≥ this skill's tier; otherwise it must hand off (run /design-feature <slug>) rather than under-power it.
• Otherwise per the project's Workflow conventions (docs-language).

Interaction & upsert (worked shape)

design-feature <slug>                → print summary → ask what to add/remove/change
design-feature <slug> "<instruction>" → apply directly, no questions, scoped to the instruction
design-feature "<new idea>"           → interview from zero (no prior SPEC to review)
design-feature <slug> "delete and redesign, <new direction>" → the only from-zero reset path

Portability (agents other than Claude Code)

The workflow is the contract; Claude Code features are conveniences. On an agent that lacks one, apply the fallback — never skip the step the feature enables:

• No slash-command menu — where this skill says /<skill>, open that skill's SKILL.md (wherever your agent installed the skills) and follow it literally, in a fresh conversation: hand-offs assume a clean context.
• No per-skill model:/effort: — on the #claude branch the frontmatter pins these tiers; here, pick tiers yourself: capability closure is judgment work — run it on your strongest model available.
• No /loop — re-invoke this skill by hand when a review round or an instruction-mode revision is needed; follow the closing → Next: block each time.

Relationship to other skills

• plan-feature redirects here (no bypass flag) when a feature's product half is not marked designed; once this skill hands off, plan-feature fills the Engineering half and scaffolds the artifacts.
• plan-feature-from-issue may compose this skill in-turn for a thin issue (only at ≥ tier — see Guardrails), or hand off to it directly.
• triage-issue's promote-to-feature verdict routes through plan-feature, which redirects here if the promoted issue is still undesigned.
• execute-phase never calls this skill — it only executes an already-planned SPEC's Engineering half.

Done when

• The Product half of the SPEC is filled and every Capability closure row is resolved (filled surface or explicit n/a).

• ## Design status accurately reflects the outcome (designed only when closure is complete).

• The roadmap row exists (created at idea if this was a brand-new feature) and its status matches the outcome — defined when designed, left at idea on NEEDS_INPUT.

• The closing → Next: block is printed:

  → Next: /plan-feature <slug> — product half designed, ready for engineering planning
    · more to design → re-run /design-feature <slug> "<instruction>" (upsert, destroys nothing)
    · recurring gap in this project's capability closure → /product-audit (a systemic pattern,
      not a one-off design fix)
  

  When ending NEEDS_INPUT instead:

  → Next: answer the pending question, then re-run /design-feature <slug>
    · unsure how to scope it → propose the smallest version and confirm