legacy-modernizer
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.
npx skills add Jeffallan/claude-skills --skill legacy-modernizer --agent claude-code
Same command for any agent — swap --agent for codex, cursor, copilot.
Weekly change comes from our own snapshots, not the repository page — it measures attention, not adoption.
# Legacy Modernizer ## Core Workflow 1. **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. 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. 3. **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. 4. **Migrate incrementally** — Apply strangler fig pattern with feature flags. Route traffic via a facade; shift load gradually. - *Validation checkpoint:* Verify error rates and latency metrics remain within baseline thresholds after each traffic increment (e.g., 5% → 25% → 50% → 100%). 5. **Validate & iterate** — Run full test suite, review
- Core Workflow
- Reference Guide
- Code Examples
- Strangler Fig Facade (Python)
- Feature Flag Wrapper
- Characterization Test Template (pytest)
- Constraints
- MUST DO
- MUST NOT DO
- Output Templates
- Knowledge Reference
What does the legacy-modernizer skill do?
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.
How do I install it?
Run `npx skills add Jeffallan/claude-skills --skill legacy-modernizer --agent claude-code` — it drops the skill into your project so the agent can pick it up. Swap the --agent value for codex, cursor or copilot if you use one of those.
Where does this skill come from?
From Jeffallan/claude-skills, a repository with 10,871 stars. We read it straight from the repository tree rather than a submitted listing, so what you see here is what is actually published.
Is a popular skill a good skill?
Not necessarily. Stars measure attention, not adoption — a repository can trend for a week and be abandoned. That is why we show the weekly change from our own snapshots next to the total, instead of a single flattering number.