redesign

name	redesign
description	Design or redesign a project's architecture from scratch. Use when the user asks about redesigning or re-architecting a project. Trigger phrases include "設計を見直したい", "アーキテクチャを再設計", "redesign this", "if I were to start over".

redesign

Analyze a project's architecture and produce a structured redesign proposal. The process has four phases: reconnaissance, analysis, dialogue, and proposal.

Unlike mechanical workflow skills, this skill is a thinking process. The goal is to deeply understand the codebase and have a genuine conversation about tradeoffs. The proposal should be honest about what works and what doesn't. If the current design is sound, say so.

Locale

Match the language the user is using in the conversation. Default to Japanese (ja) if ambiguous. All output — phase summaries, questions, the final proposal — should be in the detected locale.

Phase 1: Reconnaissance

The goal is to build a mental model of the project before forming opinions.

1.1 Determine Scope

Ask the user what they want to redesign:

• The entire project
• A specific subsystem or module
• A particular concern (e.g., data layer, API surface, deployment)

For monorepos, narrow down to specific packages before proceeding. Don't try to redesign everything at once.

1.2 Explore the Codebase

Use the Agent tool with subagent_type=Explore for thorough exploration. Work through this checklist systematically:

Area	What to look at
Structure	Directory layout, module boundaries, entry points
Dependencies	package.json, go.mod, requirements.txt, Cargo.toml, etc. — both what's used and what's surprising
Configuration	Environment variables, config files, feature flags
Data	Database schemas, migrations, data flow patterns
Tests	Test structure, coverage patterns, what's tested vs. what isn't
CI/CD	Pipeline definitions, deployment targets, build steps
Git history	Recent churn (git log --oneline -30), hot files (sort by frequency from git log output)
Documentation	README, ADRs, inline docs — what's documented vs. what's tribal knowledge

Not every area applies to every project. Skip what's irrelevant. For small projects (<5 files), a quick read-through replaces this checklist.

1.3 Assess Project Scale

Categorize the project to calibrate the depth of analysis:

Scale	Heuristic	Approach
Small	<5 files, single concern	Lightweight analysis. Often the answer is "rewrite it" rather than "redesign it."
Medium	5-50 files, a few modules	Standard four-phase process.
Large	50+ files, multiple domains	Focus on the highest-impact subsystem first. Break the redesign into scoped proposals.

1.4 Gather Constraints

Ask the user about constraints that shape the design space. Don't ask all at once — weave these into the conversation naturally:

• Domain: What the project does and the core problem it solves.
• Team: Team size and experience level.
• Deployment: Where the project runs (cloud, on-prem, edge, CLI).
• Technical constraints: Whether it must stay in the current language/framework. Integration requirements.
• Appetite for change: Whether the user wants incremental improvements or is open to a significant rewrite.
• Timeline: Whether there is urgency, or this is exploratory.

If the user doesn't know or doesn't care about some of these, use reasonable defaults and move on.

Phase 2: Analysis

The goal is to form an honest assessment of the current architecture.

2.1 Identify Strengths

Start with what's working. Every codebase has good decisions in it — find them and acknowledge them. This builds trust and ensures the proposal preserves what shouldn't change.

2.2 Classify Complexity

For each problem area you find, classify it:

• Essential complexity: Inherent to the problem domain. Can't be eliminated, only managed. (e.g., "payment processing has many edge cases" — that's the nature of payments)
• Accidental complexity: Introduced by implementation choices. Can be reduced or eliminated. (e.g., "three different HTTP clients because nobody knew the first one existed")

Focus redesign effort on accidental complexity. Essential complexity warrants better management strategies, not elimination attempts.

2.3 Pattern Recognition

Read references/analysis-patterns.md to inform your analysis. Look for:

• Which architectural patterns are currently in use (explicitly or implicitly)
• Whether the current patterns fit the project's actual needs
• Common antipatterns that are causing friction

Don't force-fit pattern names onto the codebase. If the project has its own implicit patterns that work, describe them on their own terms.

2.4 Find Hotspots

Identify specific areas of friction:

• Coupling hotspots: Changes in module A frequently require changes in module B
• Abstraction mismatches: An abstraction that doesn't match how it's used (over-abstracted or under-abstracted)
• Knowledge silos: Code that only one person understands (detectable from git blame patterns)
• Churn: Files that change in every PR (from git history)

2.5 Share Findings

Before proposing solutions, share your analysis with the user. Present it conversationally, not as a formal report. Ask for their reaction:

• "Does this match your experience."
• "Are there pain points I missed."
• "Is anything I flagged actually intentional."

This step matters. Your analysis might be wrong, and the user has context you don't.

Phase 3: Dialogue

The goal is to align on direction before writing a proposal.

3.1 Present Design Directions

Based on the analysis, present 2-3 possible directions. Typically:

1. Incremental improvement: Keep the current structure, fix the worst pain points. Low risk, fast payoff, but doesn't address structural issues.
2. Structural reorganization: Reshape module boundaries and abstractions while preserving the core. Medium risk, requires coordinated effort.
3. Clean-slate design: Design from scratch with current knowledge. High risk, high potential, but loses existing institutional knowledge embedded in the code.

For each direction, be concrete about what changes and what stays. Don't present vague platitudes — give specific examples of what the code would look like.

Not every project needs all three options. A small project might only warrant "keep it" vs. "rewrite it." Sound architectures might only need targeted fixes.

3.2 Discuss Tradeoffs

Help the user think through tensions:

• Simplicity vs. flexibility: A simpler design is easier to understand but harder to extend. Determine which matters more for this project.
• Migration speed vs. quality: Consider whether the team can afford a long migration or needs quick wins.
• Consistency vs. pragmatism: Evaluate whether rewriting working code for consistency is worthwhile.

3.3 Reach Agreement

Get explicit agreement on a direction before writing the proposal. The proposal should hold no surprises — it's a formalization of what you've already discussed.

If the user is just looking for validation that their current architecture is fine, and it is, say so clearly. Don't manufacture a redesign proposal for a codebase that doesn't need one.

Phase 4: Proposal

The goal is to produce a clear, actionable redesign document.

4.1 Generate the Proposal

Read references/output-template.md for the exact template. Fill it in based on the agreed-upon direction from Phase 3.

Key principles for the proposal:

• Grounded in evidence: Every claim references specific code, files, or patterns found during analysis. No hand-waving.
• Honest about tradeoffs: Every design decision has a cost. State it.
• Phased migration: Break the work into phases that each deliver standalone value. No "big bang" rewrites unless the project is small enough that it's actually safer.
• Risk-aware: Each phase should note what could go wrong and how to detect it.

4.2 Migration Path

The migration path is the most important part of the proposal. A beautiful target architecture is worthless without a realistic plan to get there.

For each phase:

• What changes: Specific modules, files, or boundaries that move
• Size estimate: T-shirt size (S/M/L/XL) — avoid false precision with hour estimates
• Prerequisites: What must be true before this phase can start
• Risks: What could go wrong and how to mitigate it
• Validation: How to confirm this phase succeeded before moving to the next

4.3 Present and Refine

Show the proposal to the user. Ask if anything needs adjustment. Iterate until they're satisfied.

Edge Cases

Project with No Clear Architecture

Some projects grow organically without deliberate architecture. In this case:

• Don't criticize the lack of architecture — it's a common and often reasonable outcome
• Focus on discovering the implicit patterns that do exist
• Propose a minimal structure that formalizes what's already working

User Wants Validation, Not Change

If the user is really asking "is my architecture OK", and it is:

• Clearly state that the current design is sound
• Point out specific strengths
• Suggest only minor improvements if any
• Don't manufacture problems to justify the skill's existence

Overwhelming Technical Debt

If the codebase has severe, pervasive issues:

• Be honest but kind
• Focus on the 2-3 highest-leverage changes rather than cataloging every problem
• Propose a realistic first step, not a fantasy end state

Legacy Codebase with Active Users

When the system is in production and can't be taken offline:

• Emphasize strangler fig pattern or similar incremental strategies
• Each migration phase must maintain backward compatibility
• Include rollback plans