Cobol Modernization Planning Playbook

COBOL Modernization Planning Playbook

Instructions

Use this skill to turn a large, poorly documented COBOL codebase into an actionable modernization plan, then execute migration incrementally with up-front validation.

1) Map the codebase (build a shared understanding)

1. Ask the AI to read the whole codebase and produce:
   • Program entry points
   • Execution paths across called subroutines
   • Data flows between modules
   • Dependencies spanning hundreds of files
2. Require the mapping to include implicit dependencies that often hide in:
   • Shared data structures
   • File operations that create coupling
   • Initialization sequences that affect runtime behavior

2) Assess modernization risk and candidates

Ask the AI to annotate the map with:

• High-coupling modules that are risky to change early
• Isolated components that are good early candidates
• Duplicated logic (refactoring opportunities)
• Areas of accumulated technical debt (migration risk)

3) Plan a roadmap with human decision-making

1. Have the AI propose an initial sequence of components to modernize based on risk, dependencies, and complexity.
2. Your team reviews and finalizes priorities based on:
   • Business value
   • Technical risk
   • Organizational constraints
3. Define at this stage (with human ownership):
   • Target architecture
   • Code standards
   • Integration requirements

4) Define testing and validation before changes

1. Ask the AI to draft functional tests that confirm migrated code produces identical outputs to the legacy COBOL.
2. Decide with subject-matter experts:
   • Which business scenarios require manual validation
   • Performance benchmarks the modernized components must meet

5) Execute incrementally with side-by-side validation

For each component:

• Translate COBOL logic into the target language
• Create API wrappers around legacy components that remain in place
• Build scaffolding to run old and new code side by side during transition
• Validate at each step before proceeding

6) Start small

Start with a single component/workflow with clear boundaries and moderate complexity.

Examples

• See: COBOL modernization workflow checklist
• See: Prompt pack for mapping and planning
• See: Example: component-by-component execution plan

Source

• https://claude.com/blog/how-ai-helps-break-cost-barrier-cobol-modernization