# Design And Plan

> Use to specify non-trivial behavior or interfaces, resolve requirements or tradeoffs, or produce a multi-step implementation plan. Do not use for a mechanical edit, routine status update, or execution of a settled plan.

- Skill: `lawzava/design-and-plan` (Agent Skill)
- Install (CLI): `npx skillmds@latest add lawzava/design-and-plan`
- Raw SKILL.md: https://api.skillmd.com/api/skills/lawzava/design-and-plan/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: lawzava (https://skillmd.com/u/lawzava)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/lawzava/design-and-plan

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# Design and Plan

Keep mechanical edits, status updates, and settled plans inline unless
requirements or material tradeoffs change.

## Understand the system

Read repository instructions and relevant code. Establish entry points,
callers, blast radius, the nearest convention-setting sibling, test coverage,
and any unread area that could change the decision.

Before custom design, check existing code, the standard library, native platform
features, and installed dependencies. Simplify while preserving requirements
and conventions. Defer speculative needs while preserving requested behavior
and acceptance criteria.

Resolve factual prerequisites before preference or policy questions. Present
competing sketches only for a high-impact, underconstrained, or hard-to-reverse
design. Recommend one and state its tradeoff.

Mark assumptions and blockers. Model a domain term when repeated state branches
or synchronized booleans obscure one concept. Do not force a glossary or ADR.

## Specify observable behavior

For a non-trivial behavior change, state intent, scope, non-goals, and
implementation-independent requirements before the plan. Give each requirement
concrete scenarios and an acceptance oracle.

Map each requirement ID to scenarios, implementation tasks, and evidence,
including failure and boundary cases. Separate proposed, implemented, and
verified behavior; plans prove only planning.

Describe behavior as Added, Modified, or Removed deltas. Reconcile existing
specifications with code and tests; a stale specification is not evidence.

Before choosing a format, inspect repository instructions and files for
baseline requirements and an active change. Detect them independently; a prompt
that mentions OpenSpec does not establish a repository convention. Use the
existing specification system and read whichever artifacts exist. Preserve its
requirement IDs and format. After verification, reconcile deltas into the
baseline. Archive only under an existing convention and authority.

Without an existing specification system, keep proportional requirements and
their evidence map inline unless repository convention or the user requires a
durable artifact. Do not create new directories or scaffolding. Do not run or
add an OpenSpec CLI or Node dependency. Use plain Markdown and skip a durable
plan for a small reversible change with clear scope, risks, and oracle.

## Produce an executable handoff

Name the outcome, owned files, interfaces, error behavior, acceptance criteria,
dependencies, and exact verification commands. Map each criterion to an
implementation target and local or external oracle. Start behavior tasks with a
failing test. Keep tasks sequential unless ownership is disjoint and neither
result can reshape the other.

Exclude speculative options, placeholders, unrelated cleanup, and unauthorized
commit steps. Before execution, check for missing criteria, inconsistent names,
and unresolved assumptions.