# legacy-modernizer

> Claude/Codex skill by [@jeffallan](https://omgskills.com/library/jeffallan/index.md) · 12k stars · Updated 2026-10-30

Designs incremental migration strategies, identifies service boundaries, produces dependency maps and migration roadmaps, and generates API facade designs for aging codebases. Use when modernizing legacy systems, implementing strangler fig pattern or branch by abstraction, decomposing monoliths, upgrading frameworks or languages, or reducing technical debt without disrupting business operations.

Tags: ai-agents, claude, claude-code, claude-marketplace, claude-skills

## Install

```sh
git clone https://github.com/Jeffallan/claude-skills /tmp/claude-skills && ln -s /tmp/claude-skills/skills/legacy-modernizer ~/.claude/skills/legacy-modernizer
```

## From README

Legacy Modernizer Core Workflow Assess system — Analyze codebase, dependencies, risks, and business constraints. Produce a dependency map and risk register before proceeding. Validation checkpoint: Confirm all external integrations and data contracts are documented before moving to step 2. Plan migration — Design an incremental roadmap with explicit rollback strategies per phase. Reference references/system-assessment.md for code analysis templates. Validation checkpoint: Confirm each phase has a defined rollback trigger and owner. Build safety net — Create characterization tests and monitoring before touching production code. Target 80%+ coverage of existing behavior. Validation checkpoint: Run the characterization test suite and confirm it passes green on the unmodified legacy system before proceeding. Migrate incrementally — Apply strangler fig pattern with feature flags. Route traffic via a facade; shift load gradually.

## Links

- HTML page: https://omgskills.com/library/jeffallan/claude-skills/legacy-modernizer/
- GitHub: https://github.com/Jeffallan/claude-skills
- Author: [@jeffallan](https://omgskills.com/library/jeffallan/index.md)

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