Plan Skill

Purpose

Core principle: Write plans assuming the engineer has zero codebase context. Document everything they need: which files, what code, how to test, how to verify. No guessing.

Create or update specs/{feature}/plan.md as the execution source of truth, including technical context, key decisions, phased tasks, and completion conditions.

Input

• Existing specs/constitution.md when present
• specs/{feature}/spec.md

Output

• specs/{feature}/plan.md
• specs/{feature}/spec.md when backflow is required

Steps

1. Resolve language and shared rules from specs/constitution.md when present; otherwise infer from the available workflow documents and the user's own message. Ask only if still unclear, then conduct all subsequent interaction in this language.
2. Read spec.md, extract frontmatter dependencies, user stories, and constraints, and confirm spec approval state.
   • Require spec.md to be approved before generating the execution plan
   • Read listed dependencies before planning; use them to resolve scope, sequencing, or validation constraints
3. Create the plan from references/plan-template.md.
   • Summary
   • Execution Context
   • Key Decisions
   • Requirement Coverage
   • Phases: Setup, Foundational, User Story (P1, P2, ...), Polish
   • When uncertainty could change the spec or plan structure, delegate to spec-research instead of investigating inline
4. Map out the file structure before defining tasks.
   • List which files will be created or modified and what each one is responsible for
   • Prefer smaller, focused files over large ones that do too much; files that change together should live together
   • In existing codebases, follow established patterns; if a file has grown unwieldy, include a split in the plan
5. Capture only execution-facing detail that must stay aligned during implementation.
   • Record technical context, constraints, validation strategy, and key decisions here instead of splitting them into another document
   • Reference the spec for user-facing intent rather than repeating full story prose
6. Standardize the task format.
   • - [ ] Txxx ...
   • Use (P) for parallel candidates
   • Use [USn] for story linkage
   • Assume the implementer is skilled but has little codebase or domain context; each task should be a single action that can be completed quickly and independently
   • When testing is required, make the expected test change, verification command, and expected outcome explicit instead of assuming the implementer will fill them in
   • Every task must contain the concrete content needed to execute it; do not use placeholders such as "TBD", "TODO", "implement later", "fill in details", or references like "Similar to Task N"
   • Do not defer critical details behind vague instructions such as "Add appropriate error handling" or "Write tests for the above"; spell out the required work directly
7. Add a requirement coverage map.
   • Map each user story, functional requirement, and success criterion to task IDs or phase DoD
   • If a requirement has no task or DoD coverage, add the missing task or run backflow
8. Add DoD under each phase.
   • Include checks for testing, observability, and rollback readiness
   • Write DoD as proof that the phase itself is complete
9. Express execution dependencies through phase order and task descriptions.
   • Place high-uncertainty discovery work before irreversible implementation tasks
   • Preserve spec-to-spec prerequisites in spec.md frontmatter dependencies
10. Run backflow if requirement gaps or contradictions are discovered.
    • Update spec.md
    • Reset spec.md status to draft
11. Update frontmatter.
    • Required keys: status, summary
    • Initial status: draft
    • Set status: approved when the plan is ready for implementation
12. Perform final review and keep the file within 150 lines.
    • Verify every story, requirement, and success criterion has task or DoD coverage
    • Search for placeholders and vague work instructions
    • Check that paths, task IDs, commands, and expected outputs are internally consistent
    • Remove repetition
    • Simplify wording
    • Resolve contradictions
13. In the completion message, suggest the next step.
    • After approval: spec-implement
    • If requirement changes are needed: spec-specify
    • If technical investigation is needed: spec-research

Success Criteria

• The plan combines execution design and delivery sequencing without requiring another execution document.
• The plan supports independent delivery by story.
• Every story, requirement, and success criterion has explicit task or DoD coverage.
• Each phase has a clear DoD.
• (P) marks valid parallel work.
• Every task contains concrete code, commands, and expected output — no placeholders.
• High-uncertainty work is front-loaded as spike or research tasks when needed.
• Spec frontmatter dependencies are considered before tasking.
• Backflow handling is explicit.

Completion Guidance

• Next recommended step: spec-implement
• If technical investigation is needed before proceeding: spec-research
• Include the target feature and generated plan.md path in the response