Use when designing REST or GraphQL APIs, creating OpenAPI specifications, or planning API architecture. Invoke for resource modeling, versioning strategies, pagination patterns, error handling standards.
legacy-modernizer
legacy-modernizer is an open-source backend skill for Claude Code and compatible agents, published by Jeffallan. Its author describes it as: “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, impl…”. The project has 11k stars on GitHub and is available under the MIT license. Add it to your setup with `/plugin marketplace add Jeffallan/claude-skills`.
What legacy-modernizer does
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.
Installation
Add legacy-modernizer to your agent with:
/plugin marketplace add Jeffallan/claude-skillsAlways review a skill's source before installing it. This command comes from the skill's public repository; the linked repo is the source of truth for exact setup steps.
What's inside
The SKILL.md for legacy-modernizer is organised into these sections:
- 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
When to use it
Reach for legacy-modernizer when you want backend help from your agent without writing the same instructions every session. Load the skill and the agent picks it up automatically for relevant tasks.
Strengths
- Clear MIT license — safe to read and adapt
- Ships in Jeffallan/claude-skills, an established project with 11,060 GitHub stars
- Actively maintained (recent commits)
Topics
Frequently asked questions
- What does legacy-modernizer 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 legacy-modernizer?
- Run /plugin marketplace add Jeffallan/claude-skills in your agent, then reload your skills. Review the source at https://github.com/Jeffallan/claude-skills before installing.
- Is legacy-modernizer free to use?
- Yes. legacy-modernizer is free and open source under the MIT license, so you can read, run, and adapt it within that license's terms.
- Where does legacy-modernizer come from?
- legacy-modernizer ships inside Jeffallan/claude-skills, a repository that contains 41 catalogued skills in total. The repository's 11,060 GitHub stars apply to that whole collection, not to this skill on its own.
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