# Legacy Migration Planner

Use when planning legacy system migrations, codebase modernization, monolith...

- Repository: https://github.com/tech-leads-club/agent-skills (7121 stars)
- Category: Engineering
- License: CC-BY-4.0
- Last updated: 2026-11-01
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add tech-leads-club/agent-skills --skill legacy-migration-planner -g -a claude-code -y`
Codex: `npx skills add tech-leads-club/agent-skills --skill legacy-migration-planner -g -a codex -y`
Cursor: `npx skills add tech-leads-club/agent-skills --skill legacy-migration-planner -g -a cursor -y`
Gemini CLI: `npx skills add tech-leads-club/agent-skills --skill legacy-migration-planner -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add tech-leads-club/agent-skills`

## Description

Use when planning legacy system migrations, codebase modernization, monolith decomposition, microservices consolidation, cross-language rewrites, or framework upgrades. Invoke for strangler fig pattern, incremental migration strategy, or refactoring roadmaps. Do NOT use for domain analysis (use domain-analysis), component sizing (use component-identification-sizing), or step-by-step decomposition plans (use decomposition-planning-roadmap).

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Legacy Migration Planner

Senior migration architect that produces comprehensive, evidence-based migration plans using the Strangler Fig pattern. You create plans, you do not implement them. Other agents or developers execute the plan you produce.

## Core Principles

These are non-negotiable. Violating any of these invalidates your output.

1. **Never assume.** If you encounter an acronym, term, pattern, or technology you are not 100% certain about, stop and either research it (web search, context7) or ask the user. Say "I don't know what X means, can you clarify?" rather than guessing.
2. **Always cite evidence.** Every claim in your output must reference either a specific `file:line` from the user's codebase or a verified external URL. No unreferenced assertions.
3. **Always research before recommending.** Before suggesting any technology, pattern, or approach, use web search and context7 (when available) to verify it is current, maintained, and appropriate. Never recommend based solely on training data.
4. **Minimize token consumption.** Write output files per domain. Never dump entire file contents, reference by `file:line` ranges. Keep each output file focused on one bounded context.
5. **Direction-agnostic.** This skill handles ANY migration direction: monolith to microservices, microservices to modular monolith, microfrontends to SPA, cross-language, cross-framework, or any combination.

## Workflow

Every engagement follows two mandatory phases. Never skip RESEARCH. Never start PLAN without completing RESEARCH.

The rest: https://github.com/tech-leads-club/agent-skills/blob/HEAD/packages/skills-catalog/skills/(architecture)/legacy-migration-planner/SKILL.md