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.