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legacy-modernization

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Analyze, document, and modernize legacy systems (COBOL, Mainframe, Fortran).

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Source SKILL.md: https://github.com/majiayu000/claude-skill-registry/blob/HEAD/skills/development/architecture-andreibesleaga-gabbe-4/SKILL.md

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Legacy Modernization Skill

Triggers

  • legacy code
  • cobol
  • mainframe
  • fortran
  • ibm z
  • jcl
  • db2
  • cics
  • modernization
  • rewrite
  • migration

Purpose

To respect the critical nature of legacy systems while safely guiding them toward modernization. Rule #1: Do no harm.

Capabilities

1. Code Analysis (The Archaeologist)

  • Explain Logic: Translate COBOL/Fortran business logic into plain English or Pseudocode.
  • Identify Risks: Spot GOTO spaghetti, hardcoded dates (Y2K style), and tight coupling.
  • Data Mapping: Map VSAM/Copybooks to JSON/SQL schemas.

2. Modernization Patterns

  • API Wrapping (The Facade): Create a REST/gRPC wrapper around the legacy core.
  • Strangler Fig: Incrementally replace functions with microservices.
  • Replatform: Lift-and-shift to cloud emulators (AWS Mainframe Modernization).

3. Testing Legacy

  • Characterization Tests: "Lock down" current behavior before changing ANYTHING.
  • Golden Master: Capture inputs/outputs of the old system to verify the new one.

Instructions

  1. Assume Importance: If it's running, it's making money. Treat legacy code with reverence.
  2. No Big Bang: Never suggest a full rewrite from scratch unless the system is < 10k LOC.
  3. Document First: most legacy failures happen because nobody knows what the code does.

Deliverables

  • legacy-analysis.md: Explanation of flow.
  • wrapper-api.yaml: OpenAPI spec for the legacy system.
  • strangler-plan.md: Step-by-step migration path.