Agent-Skills.md

Agent Skills: Legacy Modernization

Modernize legacy systems using proven migration patterns like strangler fig, feature flags, and incremental refactoring. Use when planning system migrations, modernizing monoliths, or managing technical debt.

UncategorizedID: NickCrew/claude-cortex/legacy-modernization

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NickCrew/claude-cortex
NickCrewLicense: MIT
93

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pnpm dlx add-skill https://github.com/NickCrew/claude-cortex/tree/HEAD/skills/legacy-modernization

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skills/legacy-modernization/SKILL.md

Skill Metadata

Name
legacy-modernization
Description
Modernize legacy systems using proven migration patterns like strangler fig, feature flags, and incremental refactoring. Use when planning system migrations, modernizing monoliths, or managing technical debt.

Legacy Modernization

Expert guidance for safe, incremental modernization of legacy systems, frameworks, and dependencies using proven migration patterns and risk mitigation strategies.

When to Use This Skill

  • Planning framework migrations (jQuery to React, Java 8 to 17, Python 2 to 3)
  • Decomposing monoliths into microservices or modular architectures
  • Modernizing databases (stored procedures to ORMs, schema migrations)
  • Reducing technical debt with a phased, low-risk approach
  • Updating outdated dependencies with backward compatibility concerns
  • Establishing test coverage for untested legacy code before refactoring
  • Designing rollback procedures for migration phases
  • Implementing feature flags for gradual rollout of modernized components

Quick Reference

| Task | Load reference | | --- | --- | | Strangler fig, feature flags, migration checklists, rollback procedures | skills/legacy-modernization/references/modernization-patterns.md |

Workflow

1. Assessment

Inventory legacy components, risks, and dependencies before changing anything.

  • Map the dependency graph and identify high-risk areas
  • Define modernization goals and phased milestones
  • Establish success metrics (test coverage, performance, defect rate)
  • Prioritize based on business value and risk

2. Safety Net Setup

Establish guardrails before any migration work begins.

  • Add characterization tests for existing behavior
  • Set up feature flags for gradual rollout
  • Create compatibility layers and adapter interfaces
  • Document current behavior and integration points

3. Incremental Execution

Apply the strangler fig pattern: replace components one at a time.

  • Route traffic gradually to new implementations
  • Maintain backward compatibility at every step
  • Run old and new paths in parallel where possible
  • Monitor for regressions continuously

4. Stabilization

Validate the migration and retire legacy paths.

  • Run full regression suites against new implementations
  • Monitor adoption metrics and error rates
  • Deprecate and remove legacy code paths
  • Document the new architecture and migration decisions

Common Mistakes

  • Attempting big-bang rewrites instead of incremental migration
  • Refactoring without tests covering existing behavior
  • Removing backward compatibility before all consumers migrate
  • Skipping rollback planning for each migration phase
  • Ignoring data migration complexity and state synchronization
  • Not involving stakeholders in deprecation timelines