Plans large-scale refactoring campaigns across codebases. Analyzes dependency graphs, calculates
blast radius, designs migration strategies, and creates incremental plans that keep the system
deployable at every step. The strategist to the refactoring-surgeon's operator.
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Plans large-scale refactoring campaigns across codebases. Analyzes dependency graphs, calculates
blast radius, designs migration strategies, and creates incremental plans that keep the system
deployable at every step. The strategist to the refactoring-surgeon's operator.
[{"skill":"refactoring-surgeon","reason":"Architect plans, surgeon executes individual refactoring steps"},{"skill":"code-architecture","reason":"Understands the target architecture being refactored toward"},{"skill":"dependency-management","reason":"Dependency graph analysis is foundational to safe refactoring order"},{"skill":"test-automation-expert","reason":"Tests are the safety net that makes incremental refactoring possible"},{"skill":"monorepo-management","reason":"Cross-package refactoring in monorepos requires package-aware planning"}]
Refactor Architect
Plans and coordinates large-scale refactoring campaigns. Analyzes dependency graphs to determine
safe execution order, designs migration strategies that keep the system deployable at every step,
calculates blast radius of proposed changes, and creates incremental plans that multiple developers
or agents can execute in parallel.
Activation Triggers
Use this skill when:
A refactoring affects more than 5 files or crosses package/module boundaries
You need to rename a widely-used interface, type, or function
A database schema migration requires coordinated application code changes
You are migrating from one API version to another across consumers
A type system upgrade (e.g., stricter TypeScript config) will break many files
You need to split a monolith module into separate packages
You are planning a codebase-wide pattern migration (e.g., class components to hooks)
The refactoring must be done incrementally because the system cannot go offline
Do NOT use this skill for:
Refactoring a single file or function (use refactoring-surgeon)
Planning new architecture from scratch (use code-architecture)
Database-only migrations with no application code impact (use database-migration-manager)
Dependency version upgrades with no API changes (use dependency-management)
Core Capabilities
1. Dependency Graph Analysis
Before touching anything, map what depends on what.
=== Blast Radius Report ===
Target: Rename UserService.getUser() -> UserService.findUser()
Changed files (1):
src/services/user-service.ts
Directly affected (8):
src/routes/user-routes.ts
src/routes/admin-routes.ts
src/middleware/auth.ts
src/controllers/user-controller.ts
src/controllers/admin-controller.ts
src/jobs/user-sync.ts
src/jobs/cleanup.ts
tests/services/user-service.test.ts
Transitively affected (12):
src/routes/index.ts
src/app.ts
tests/routes/user-routes.test.ts
tests/routes/admin-routes.test.ts
...
Risk level: HIGH (21 files affected)
Recommendation: Split into 3 PRs over 2 days.
PR 1: Add findUser() as alias, deprecate getUser() [0 breakage]
PR 2: Migrate all callers to findUser() [0 breakage]
PR 3: Remove getUser() [0 breakage if PR 2 is complete]
3. Safe Refactoring Order
Topological sort of the dependency graph gives you the order in which files can be
safely modified without breaking intermediate states:
functioncomputeSafeRefactoringOrder(graph: DepGraph,
affectedFiles: string[]
): RefactoringWave[] {
// Build sub-graph of only affected filesconst inDegree = newMap<string, number>();
const subEdges = newMap<string, Set<string>>();
for (const file of affectedFiles) {
inDegree.set(file, 0);
subEdges.set(file, newSet());
}
for (const file of affectedFiles) {
const deps = graph.imports.get(file) || newSet();
for (const dep of deps) {
if (affectedFiles.includes(dep)) {
subEdges.get(dep)!.add(file);
inDegree.set(file, (inDegree.get(file) || 0) + 1);
}
}
}
// Kahn's algorithm — group into waves (same as DAG wave computation)constwaves: RefactoringWave[] = [];
let remaining = newSet(affectedFiles);
while (remaining.size > 0) {
const wave = [...remaining].filter(f => (inDegree.get(f) || 0) === 0);
if (wave.length === 0) {
// Cycle detected — these files have circular dependencies
waves.push({ files: [...remaining], parallel: false, note: 'CIRCULAR — manual ordering required' });
break;
}
waves.push({ files: wave, parallel: true, note: `Wave ${waves.length + 1}: safe to modify in parallel` });
for (const file of wave) {
remaining.delete(file);
for (const dependent of subEdges.get(file) || []) {
inDegree.set(dependent, (inDegree.get(dependent) || 0) - 1);
}
}
}
return waves;
}
interfaceRefactoringWave {
files: string[];
parallel: boolean;
note: string;
}
Output example:
=== Refactoring Order (4 waves) ===
Wave 1 (parallel-safe):
src/types/user.ts — Change the type definition first
src/types/admin.ts — Also independent
Wave 2 (parallel-safe):
src/services/user-service.ts — Update service (depends on types)
src/services/admin-service.ts — Update service (depends on types)
Wave 3 (parallel-safe):
src/controllers/user-controller.ts — Update consumers of services
src/controllers/admin-controller.ts
src/middleware/auth.ts
src/jobs/user-sync.ts
Wave 4 (parallel-safe):
src/routes/user-routes.ts — Update route wiring (depends on controllers)
src/routes/admin-routes.ts
tests/**/*.test.ts — Update tests last (they verify the new state)
4. Migration Strategy Patterns
Pattern A: Expand-Contract (Parallel Change)
The safest pattern for API changes. Three phases, each independently deployable:
Phase 1: EXPAND — Add the new alongside the old
- New method/field/endpoint exists
- Old method/field/endpoint still works
- All tests pass, nothing breaks
Phase 2: MIGRATE — Move consumers to the new
- Update all callers one by one
- Each caller migration is a separate commit
- Old method/field/endpoint still works (for safety)
Phase 3: CONTRACT — Remove the old
- Delete deprecated method/field/endpoint
- Remove any shim/adapter code
- Final cleanup
Pattern B: Strangler Fig (Module Replacement)
For replacing an entire module or subsystem:
1. Identify the boundary (imports into and out of the module)
2. Create the new module with the same public interface
3. Route traffic/calls through a facade that delegates:
- Initially 100% to old module
- Gradually shift to new module (feature flag or config)
- Monitor for errors at each percentage
4. When new module handles 100%, remove old module and facade
Pattern C: Branch by Abstraction
For replacing a dependency that is deeply woven into the codebase:
1. Create an abstraction layer (interface) in front of the old dependency
2. Make all existing code use the abstraction instead of the dependency directly
3. Create a second implementation of the abstraction using the new dependency
4. Switch the implementation (DI container, factory, config flag)
5. Remove the old implementation and the abstraction (if only one impl remains)
Pattern D: Database Schema Evolution
For schema changes that require coordinated app changes:
Step 1: Deploy app that WRITES to both old and new schema
Step 2: Backfill — migrate existing data to new schema
Step 3: Deploy app that READS from new schema
Step 4: Deploy app that stops WRITING to old schema
Step 5: Drop old columns/tables
NEVER: Change schema and app code in the same deployment.
5. Multi-Agent Refactoring Plans
When the refactoring is large enough to parallelize across agents or developers:
# refactoring-plan.yamlcampaign:rename-getUser-to-findUserstrategy:expand-contractestimated_waves:4estimated_duration:2daysphases:-name:expanddescription:AddfindUser()asanaliasforgetUser()files:-src/services/user-service.tsverification:npmtestpr_title:"refactor: add findUser() alias (expand phase)"-name:migrate-wave-1description:Migratecontrollersandmiddlewareparallel:truefiles:-src/controllers/user-controller.ts-src/controllers/admin-controller.ts-src/middleware/auth.tsverification:npmtestdepends_on:expandpr_title:"refactor: migrate controllers to findUser()"-name:migrate-wave-2description:Migratebackgroundjobsandtestsparallel:truefiles:-src/jobs/user-sync.ts-src/jobs/cleanup.ts-tests/services/user-service.test.ts-tests/controllers/*.test.tsverification:npmtestdepends_on:migrate-wave-1pr_title:"refactor: migrate jobs and tests to findUser()"-name:contractdescription:RemovedeprecatedgetUser()files:-src/services/user-service.tsverification:|
npm test
grep -r "getUser" src/ --include="*.ts" && exit 1 || exit 0
depends_on:migrate-wave-2pr_title:"refactor: remove deprecated getUser()"
6. Import Graph Rewiring
When reorganizing modules (moving files, splitting packages), the import graph must be
systematically updated. Approach:
# 1. Find all imports of the file being moved
grep -rn "from ['\"].*old-path" src/ --include="*.ts" --include="*.tsx"# 2. Generate a sed script for the rename
find src -name '*.ts' -o -name '*.tsx' | xargs sed -i '' \
"s|from ['\"]\.\.\/services\/user-service['\"]|from '../services/identity/user-service'|g"# 3. Verify no broken imports
npx tsc --noEmit 2>&1 | grep "Cannot find module" || echo"All imports resolved"# 4. Verify no circular dependencies introduced
npx madge --circular src/
Automated verification after each wave:
tsc --noEmit -- type checker confirms all imports resolve
npx madge --circular src/ -- no new circular dependencies
npm test -- behavior is unchanged
git diff --stat -- confirms only expected files changed
Decision Points
When to use Expand-Contract vs. Big Bang
Factor
Expand-Contract
Big Bang
Change scope
> 10 files
< 5 files, all in one module
Deployment risk
Low (each phase is safe)
High (all or nothing)
Team coordination
Multiple developers/agents
Single developer
Rollback cost
Trivial (revert one phase)
Painful (revert everything)
Duration
Days to weeks
Hours
When to use
Production systems, shared APIs
Internal tools, early-stage code
When to split into multiple PRs
Always split if the total diff exceeds 500 lines
Always split if changes cross package boundaries in a monorepo
Always split if different parts of the change have different risk levels
OK to merge if the entire change is under 200 lines and touches one module
How to handle circular dependencies during refactoring
Identify the cycle: npx madge --circular src/
Determine which edge in the cycle is the "wrong" direction
Extract the shared dependency into its own module (break the cycle)
Update imports on both sides
Verify: npx madge --circular src/ should show one fewer cycle
Anti-Patterns
1. Planning without a dependency graph
Symptom: "Let's just rename this interface everywhere" without knowing what "everywhere" means
Why wrong: You will miss transitive consumers, break CI for other teams, and spend days debugging
Fix: Build or generate the dependency graph first. Every refactoring plan starts with blast radius.
2. Monolithic refactoring PRs
Symptom: A 3000-line PR titled "refactor: modernize user module"
Why wrong: Unreviewable, unrevertable, blocks the main branch for days
Fix: Split by wave. Each wave is a PR. Each PR is reviewable in 15 minutes.
3. Skipping the expand phase
Symptom: Renaming a function and updating all callers in one commit
Why wrong: If any caller was missed (dynamic imports, config files, scripts), the deploy breaks
Fix: Always add the new name alongside the old, migrate callers, then remove the old name.
4. Refactoring without a verification step per wave
Symptom: "We'll run tests after the whole refactoring is done"
Why wrong: When tests fail, you don't know which wave introduced the failure
Fix: npm test after every wave. If tests fail, fix before moving to the next wave.
5. Changing interfaces and implementations simultaneously
Symptom: Modifying a service's public API and its internal logic in the same PR
Why wrong: If a bug appears, you can't tell if it's from the API change or the logic change
Fix: Separate PRs. First change the interface shape (with the old behavior). Then change the behavior.
6. Ignoring downstream consumers outside the repo
Symptom: Renaming an API endpoint without checking who calls it
Fix: Check API access logs, search for the endpoint in other repositories, notify consumers before the contract phase.
7. Planning the entire campaign upfront with no feedback loops
Symptom: A 50-page refactoring document that becomes stale after the first wave
Fix: Plan 2-3 waves ahead. After each wave, reassess. The dependency graph may change as you refactor.
Quality Checklist
Dependency graph is built and blast radius is calculated before any code changes
Risk level is categorized (low/medium/high/critical) and communicated to stakeholders
Migration strategy is chosen (expand-contract, strangler fig, branch by abstraction) and documented
Refactoring is broken into waves, each independently deployable
Each wave has a verification step (tests, type check, circular dependency check)
No wave introduces circular dependencies
Each wave's PR is under 500 lines of diff
The system is deployable and functional after every wave (no intermediate broken states)
Downstream consumers outside the repo are identified and notified
Rollback plan exists for each phase (usually: revert the PR)
The refactoring plan is a living document, updated after each wave
All renamed/moved symbols have their old names available during the migration period
Automated tooling (sed, codemod, IDE refactor) is preferred over manual find-replace
Test coverage for affected areas is verified before starting (add tests if gaps exist)
