Legacy Modernization & Migration

For engineers in legacy code: modernize incrementally, no big-bang rewrite. — built in-house by Skill Me.

Reach for this when you inherit a business-critical codebase that has to keep running while you drag it onto a modern stack. Plan a strangler-fig migration that runs old and new side by side, carve one safe bounded-context seam out of a monolith, drive major framework and language-version upgrades as small reversible CI-gated PRs, recover the business rules buried in tangled code, pin current behavior with characterization tests before you touch it, audit dependency risk as you upgrade, and delete dead code with evidence - so nothing breaks while everything moves.

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Install

  • From the catalog: skillme.dev/pack/legacy-modernization — install the whole pack into Claude in one step.
  • With the skills CLI: npx skills add SkillMedev/legacy-modernization
  • Manually: copy any skills/<slug>/SKILL.md into your Claude skills directory.

Skills in this pack

  • Strangler Fig Planner — Produces an incremental migration plan that runs a legacy and a new system side by side behind a routing seam, slicing and sequencing whole capabilities so the old system stays live until its last route is cut.
  • Framework Upgrader — Drives a major-version framework bump as a sequence of small, reversible, CI-gated PRs using official codemods and changelog diffing while keeping the app green.
  • Language Version Migrator — Ports a codebase across a breaking language or runtime version with compatibility shims, batched automated transforms, dual-runtime CI, and old-vs-new output diffing, ending in a flag-flip cutover with a rollback rule.
  • Business Rule Extractor — Produces a documented inventory of the implicit business rules, edge cases, and bug-as-feature behaviors that tangled code encodes, with real input-to-output examples, so a rewrite preserves behavior.
  • Characterization Test Writer — Writes pinning and characterization tests that lock in the current behavior of untested legacy code - bugs included - before a refactor, so any later behavior change trips an alarm.
  • Dead Code Eliminator — Proves code is unreachable with converging evidence, then removes it and its tests, fixtures, and flags in reversible slices without breaking dynamic callers.
  • Monolith Decomposer — Finds and validates one bounded-context seam to extract from a monolith - gated on coupling-graph, co-change, data-ownership, and transaction-boundary evidence - and sequences an incremental strangler-fig extraction plan.
  • Dependency Risk Audit — Audits third-party dependencies for exploitable CVEs, abandonment, license exposure, and supply-chain hygiene, and delivers a ranked findings report with a remediation order.
  • TDD Expert — Drive development with strict Red-Green-Refactor discipline - write one failing test, write the minimum code to pass it, refactor on green - including test-list planning and a worked kata cycle.

License

MIT — see LICENSE. Skills are portable SKILL.md files; the canonical copies live in the Skill Me catalog.