Agent skill

code-migration

Use when migrating codebases between frameworks, languages, versions, or platforms. Provides migration assessment patterns, planning templates, framework-specific migration examples, testing strategies, rollback procedures, and automation approaches.

View SKILL.md on GitHub Repository
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Install this agent skill to your Project

npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/other/other/code-migration

SKILL.md

Code Migration

Migration Assessment

Complexity Factors

Factor Considerations
Size File count, LOC, component count
Architectural Coupling, layer separation, pattern usage
Dependency Third-party libs, version constraints, compatibility
Business Logic Complexity of rules, domain knowledge needed
Data Schema migrations, data transformations, integrity

Risk Patterns to Scan

python
risk_patterns = {
    'global_state': { 'pattern': r'(global|window)\.\w+\s*=', 'severity': 'high' },
    'direct_dom': { 'pattern': r'document\.(getElementById|querySelector)', 'severity': 'medium' },
    'async_patterns': { 'pattern': r'(callback|setTimeout|setInterval)', 'severity': 'medium' },
    'deprecated_apis': { 'pattern': r'(componentWillMount|componentWillReceiveProps)', 'severity': 'high' }
}

Migration Planning

Simple Migration (complexity < 3):

Phase Duration Tasks
Preparation 1 week Setup project, install deps, configure build, setup testing
Core Migration 2-3 weeks Migrate utilities, port components, update models, migrate logic
Testing 1 week Unit, integration, performance testing, bug fixes

Complex Migration (complexity >= 3):

Phase Duration Tasks
Foundation 2 weeks Architecture design, PoC, tool selection, team training
Infrastructure 3 weeks Build pipeline, dev environment, core abstractions
Incremental 6-8 weeks Feature modules, adapters/bridges, dual runtime
Cutover 2 weeks Complete remaining, remove legacy, optimize, final testing

Framework Migration: React to Vue

javascript
// JSX to Template conversions
template = template.replace(/className=/g, 'class=');
template = template.replace(/onClick={/g, '@click="');
template = template.replace(/{(\w+) && (.+?)}/g, '<template v-if="$1">$2</template>');
template = template.replace(/{(\w+)\.map\(.*?\)}/g, '<template v-for="...">...</template>');

// Lifecycle mapping
lifecycleMapping = {
    'componentDidMount': 'mounted',
    'componentDidUpdate': 'updated',
    'componentWillUnmount': 'beforeDestroy',
    'getDerivedStateFromProps': 'computed'
};

Framework Migration: Python 2 to 3

python
# Key transformations
'.iteritems()' -> '.items()'
'.iterkeys()' -> '.keys()'
'xrange' -> 'range'
'.has_key(' -> ' in '
'print statement' -> 'print()'
'print >> file,' -> 'print(..., file=file)'

Framework Migration: REST to GraphQL

javascript
// Map REST endpoints to GraphQL
// GET /resources -> Query { resources }
// POST /resources -> Mutation { createResource }
// PUT /resources/:id -> Mutation { updateResource }
// DELETE /resources/:id -> Mutation { deleteResource }

Database: SQL to NoSQL

python
# Design decisions for document structure
for rel in relationships:
    if rel['type'] == 'one-to-one' or should_embed(rel):
        # Embed related data in document
        structure['embedded'].append(rel)
    else:
        # Store reference (foreign key equivalent)
        structure['references'].append(rel)

# Batch migration pattern
async def migrate_table(table, mapping):
    async for batch in read_in_batches(table, batch_size=1000):
        documents = [transform_row_to_document(row, mapping) for row in batch]
        await nosql[mapping['collection']].insert_many(documents)

Rollback Triggers

Condition Threshold Detection
Critical functionality broken Any P0 feature Automated monitoring
Performance degradation >50% response time increase APM metrics
Data corruption Any integrity issues Data validation checks
High error rate >5% error rate increase Error tracking

Rollback by Strategy

  • Blue-Green: Switch load balancer back to blue environment
  • Canary: Shift traffic back to stable version
  • Feature Flag: Toggle flag off, monitor recovery

Key Deliverables Checklist

  • Migration analysis of source codebase
  • Risk assessment with mitigation strategies
  • Phased migration plan with timeline
  • Automated migration scripts
  • Comparison tests and validation
  • Rollback procedures
  • Progress tracking and monitoring

Agent Team Mode

For large codebases (>50 files affected) or multi-module migrations where independent subsystems can be migrated in parallel.

Team Configuration

yaml
team:
  recommended_size: 3-5
  agent_roles:
    - name: module-migrator-N
      type: general-purpose
      focus: "Migrate assigned module/subsystem independently"
      skills_loaded: ["migration:code-migration"]
    - name: migration-reviewer
      type: Explore
      focus: "Validate each migration against comparison tests and compatibility"
      skills_loaded: ["migration:code-migration", "testing:language-testing-patterns"]
  file_ownership: "by-module"
  lead_mode: "delegate"

Team Workflow

  1. Lead runs Migration Assessment phase — complexity analysis, dependency graph, risk patterns
  2. Lead creates phased plan, assigns independent modules to module-migrator teammates
  3. Each module-migrator owns their file set exclusively — no cross-module edits
  4. migration-reviewer validates each completed module (tests pass, API compatibility, no regressions)
  5. Lead handles integration phase — cross-module wiring, full test suite, rollback preparation

File Ownership Example

module-migrator-1:
  files: src/auth/**
  constraint: Do NOT modify files outside this path

module-migrator-2:
  files: src/payments/**
  constraint: Do NOT modify files outside this path

Single-Agent Fallback

Without team mode, execute all phases sequentially (default behavior). Team mode is an optional enhancement.

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