Paths: File paths (shared/, references/, ../ln-*) are relative to skills repo root. If not found at CWD, locate this SKILL.md directory and go up one level for repo root.

Code Quality Checker

Analyzes Done implementation tasks with quantitative Code Quality Score based on metrics, MCP Ref validation, and issue penalties.

Purpose & Scope

• Load Story and Done implementation tasks (exclude test tasks)
• Calculate Code Quality Score using metrics and issue penalties
• MCP Ref validation: Verify optimality, best practices, and performance via external sources
• Check for DRY/KISS/YAGNI violations, architecture boundary breaks, security issues
• Produce quantitative verdict with structured issue list; never edits Linear or kanban

Code Metrics

Metric	Threshold	Penalty
Cyclomatic Complexity	≤10 OK, 11-20 warning, >20 fail	-5 (warning), -10 (fail) per function
Function size	≤50 lines OK, >50 warning	-3 per function
File size	≤500 lines OK, >500 warning	-5 per file
Nesting depth	≤3 OK, >3 warning	-3 per instance
Parameter count	≤4 OK, >4 warning	-2 per function

Code Quality Score

Formula: Code Quality Score = 100 - metric_penalties - issue_penalties

Issue penalties by severity:

Severity	Penalty	Examples
high	-20	Security vulnerability, O(n²)+ algorithm, N+1 query
medium	-10	DRY violation, suboptimal approach, missing config
low	-3	Naming convention, minor code smell

Score interpretation:

Score	Status	Verdict
90-100	Excellent	PASS
70-89	Acceptable	CONCERNS
<70	Below threshold	ISSUES_FOUND

Issue Prefixes

Prefix	Category	Default Severity	MCP Ref
SEC-	Security (auth, validation, secrets)	high	—
PERF-	Performance (algorithms, configs, bottlenecks)	medium/high	✓ Required
MNT-	Maintainability (DRY, SOLID, complexity, dead code)	medium	—
ARCH-	Architecture (layers, boundaries, patterns, contracts)	medium	—
BP-	Best Practices (implementation differs from recommended)	medium	✓ Required
OPT-	Optimality (better approach exists for this goal)	medium	✓ Required

OPT- subcategories:

Prefix	Category	Severity
OPT-OSS-	Open-source replacement available (cross-ref ln-645 audit)	medium (high if >200 LOC)

ARCH- subcategories:

Prefix	Category	Severity
ARCH-LB-	Layer Boundary: I/O outside infra, HTTP in domain	high
ARCH-TX-	Transaction Boundaries: commit() in 3+ layers, mixed UoW ownership	high (CRITICAL if auth/payment)
ARCH-DTO-	Missing DTO (4+ params without DTO), Entity Leakage (ORM entity in API response)	medium (high if auth/payment)
ARCH-DI-	Dependency Injection: direct instantiation in business logic, mixed DI+imports	medium
ARCH-CEH-	Centralized Error Handling: no global handler, stack traces in prod, uncaughtException	medium (high if no handler at all)
ARCH-SES-	Session Ownership: DI session + local session in same module	medium
ARCH-AI-SEB	Side-Effect Breadth: 3+ side-effect categories in one function	medium
ARCH-AI-AH	Architectural Honesty: read-named function with write side-effects	medium
ARCH-AI-FO	Flat Orchestration: service imports 3+ other services	medium

PERF- subcategories:

Prefix	Category	Severity
PERF-ALG-	Algorithm complexity (Big O)	high if O(n²)+
PERF-CFG-	Package/library configuration	medium
PERF-PTN-	Architectural pattern performance	high
PERF-DB-	Database queries, indexes	high

MNT- subcategories:

Prefix	Category	Severity
MNT-DC-	Dead code: replaced implementations, unused exports/re-exports, backward-compat wrappers, deprecated aliases	medium (high if public API)
MNT-DRY-	DRY violations: duplicate logic across files	medium
MNT-GOD-	God Classes: class with >15 methods or >500 lines (not just file size)	medium (high if >1000 lines)
MNT-SIG-	Method Signature Quality: boolean flag params, unclear return types, inconsistent naming, >5 optional params	low
MNT-ERR-	Error Contract inconsistency: mixed raise + return None in same service	medium

When to Use

• Invoked by ln-510-quality-coordinator Phase 2
• All implementation tasks in Story status = Done
• Before ln-512 tech debt cleanup and ln-513 agent review

Workflow (concise)

1. Load Story (full) and Done implementation tasks (full descriptions) via Linear; skip tasks with label "tests".

2. Collect affected files from tasks (Affected Components/Existing Code Impact) and recent commits/diffs if noted.

3. Calculate code metrics:

   • Cyclomatic Complexity per function (target ≤10)
   • Function size (target ≤50 lines)
   • File size (target ≤500 lines)
   • Nesting depth (target ≤3)
   • Parameter count (target ≤4)

4. MCP Ref Validation (MANDATORY for code changes — SKIP if --skip-mcp-ref flag passed):

   Fast-track mode: When invoked with --skip-mcp-ref, skip this entire step (no OPT-, BP-, PERF- checks). Proceed directly to step 5 (static analysis). This reduces cost from ~5000 to ~800 tokens while preserving metrics + static analysis coverage.

   Level 1 — OPTIMALITY (OPT-):

   • Extract goal from task (e.g., "user authentication", "caching", "API rate limiting")
   • Research alternatives: ref_search_documentation("{goal} approaches comparison {tech_stack} 2026")
   • Compare chosen approach vs alternatives for project context
   • Flag suboptimal choices as OPT- issues

   Level 2 — BEST PRACTICES (BP-):

   • Research: ref_search_documentation("{chosen_approach} best practices {tech_stack} 2026")
   • For libraries: query-docs(library_id, "best practices implementation patterns")
   • Flag deviations from recommended patterns as BP- issues

   Level 3 — PERFORMANCE (PERF-):

   • PERF-ALG: Analyze algorithm complexity (detect O(n²)+, research optimal via MCP Ref)
   • PERF-CFG: Check library configs (connection pooling, batch sizes, timeouts) via query-docs
   • PERF-PTN: Research pattern pitfalls: ref_search_documentation("{pattern} performance bottlenecks")
   • PERF-DB: Check for N+1, missing indexes via query-docs(orm_library_id, "query optimization")

   Triggers for MCP Ref validation:

   • New dependency added (package.json/requirements.txt changed)
   • New pattern/library used
   • API/database changes
   • Loops/recursion in critical paths
   • ORM queries added

5. Analyze code for static issues (assign prefixes): MANDATORY READ: shared/references/clean_code_checklist.md

   • SEC-: hardcoded creds, unvalidated input, SQL injection, race conditions
   • MNT-: DRY violations (MNT-DRY-: duplicate logic), dead code (MNT-DC-: per checklist), complex conditionals, poor naming
   • MNT-DRY- cross-story hotspot scan: Grep for common pattern signatures (error handlers: catch.*Error|handleError, validators: validate|isValid, config access: getSettings|getConfig) across ALL src/ files (count mode). If any pattern appears in 5+ files, sample 3 files (Read 50 lines each) and check structural similarity. If >80% similar → MNT-DRY-CROSS (medium, -10 points): Pattern X duplicated in N files — extract to shared module.
   • MNT-DC- cross-story unused export scan: For each file modified by Story, count export declarations. Then Grep across ALL src/ for import references to those exports. Exports with 0 import references → MNT-DC-CROSS (medium, -10 points): {export} in {file} exported but never imported — remove or mark internal.
   • OPT-OSS- cross-reference ln-645 (static, fast-track safe): IF docs/project/.audit/ln-640/*/645-open-source-replacer*.md exists (glob across dates, take latest), check if any HIGH-confidence replacement matches files changed in current Story. IF match found → create OPT-OSS-{N} issue with module path, goal, recommended package, confidence, stars, license from ln-645 report. Severity: high if >200 LOC, medium otherwise. This check reads local files only — no MCP calls — runs even with --skip-mcp-ref.
   • ARCH-: layer violations, circular dependencies, guide non-compliance
   • ARCH-LB-: layer boundary violations (HTTP/DB/FS calls outside infrastructure layer)
   • ARCH-TX-: transaction boundary violations (commit() across multiple layers)
   • ARCH-DTO-: missing DTOs (4+ repeated params), entity leakage (ORM entities returned from API)
   • ARCH-DI-: direct instantiation in business logic (no DI container or mixed patterns)
   • ARCH-CEH-: centralized error handling absent or bypassed
   • ARCH-SES-: session ownership conflicts (DI + local session in same module)
   • ARCH-AI-SEB: side-effect breadth (3+ categories in one function)
   • ARCH-AI-AH: architectural honesty (read-named function with hidden writes)
   • ARCH-AI-FO: flat orchestration (service importing 3+ services)
   • MNT-GOD-: god classes (>15 methods or >500 lines per class)
   • MNT-SIG-: method signature quality (boolean flags, unclear returns)
   • MNT-ERR-: error contract inconsistency (mixed raise/return patterns in same service)

6. Calculate Code Quality Score:

   • Start with 100
   • Subtract metric penalties (see Code Metrics table)
   • Subtract issue penalties (see Issue penalties table)

7. Output verdict with score and structured issues. Add Linear comment with findings.

Critical Rules

• Read guides mentioned in Story/Tasks before judging compliance.
• MCP Ref validation: For ANY architectural change, MUST verify via ref_search_documentation before judging.
• Context7 for libraries: When reviewing library usage, query-docs to verify correct patterns.
• Language preservation in comments (EN/RU).
• Do not create tasks or change statuses; caller decides next actions.

Definition of Done

• Story and Done implementation tasks loaded (test tasks excluded).
• Code metrics calculated (Cyclomatic Complexity, function/file sizes).
• MCP Ref validation completed:
  • OPT-: Optimality checked (is chosen approach the best for the goal?)
  • BP-: Best practices verified (correct implementation of chosen approach?)
  • PERF-: Performance analyzed (algorithms, configs, patterns, DB)
• ARCH- subcategories checked (LB, TX, DTO, DI, CEH, SES); MNT- subcategories checked (DC, DRY, GOD, SIG, ERR).
• Issues identified with prefixes and severity, sources from MCP Ref/Context7.
• Code Quality Score calculated.
• Output format:

  verdict: PASS | CONCERNS | ISSUES_FOUND
  code_quality_score: {0-100}
  metrics:
    avg_cyclomatic_complexity: {value}
    functions_over_50_lines: {count}
    files_over_500_lines: {count}
  issues:
    # OPTIMALITY
    - id: "OPT-001"
      severity: medium
      file: "src/auth/index.ts"
      goal: "User session management"
      finding: "Suboptimal approach for session management"
      chosen: "Custom JWT with localStorage"
      recommended: "httpOnly cookies + refresh token rotation"
      reason: "httpOnly cookies prevent XSS token theft"
      source: "ref://owasp-session-management"
  
    # OPTIMALITY - OSS Replacement (from ln-645, fast-track safe)
    - id: "OPT-OSS-001"
      severity: high
      file: "src/utils/email-validator.ts"
      goal: "Email validation with MX checking"
      finding: "Custom 245-line module has HIGH-confidence OSS replacement"
      chosen: "Custom email-validator.ts (245 lines)"
      recommended: "zod + zod-email (28k stars, MIT, 95% coverage)"
      reason: "Battle-tested, actively maintained, reduces maintenance burden"
      source: "ln-645-audit"
  
    # BEST PRACTICES
    - id: "BP-001"
      severity: medium
      file: "src/api/routes.ts"
      finding: "POST for idempotent operation"
      best_practice: "Use PUT for idempotent updates (RFC 7231)"
      source: "ref://api-design-guide#idempotency"
  
    # PERFORMANCE - Algorithm
    - id: "PERF-ALG-001"
      severity: high
      file: "src/utils/search.ts:42"
      finding: "Nested loops cause O(n²) complexity"
      current: "O(n²) - nested filter().find()"
      optimal: "O(n) - use Map/Set for lookup"
      source: "ref://javascript-performance#data-structures"
  
    # PERFORMANCE - Config
    - id: "PERF-CFG-001"
      severity: medium
      file: "src/db/connection.ts"
      finding: "Missing connection pool config"
      current_config: "default (pool: undefined)"
      recommended: "pool: { min: 2, max: 10 }"
      source: "context7://pg#connection-pooling"
  
    # PERFORMANCE - Database
    - id: "PERF-DB-001"
      severity: high
      file: "src/repositories/user.ts:89"
      finding: "N+1 query pattern detected"
      issue: "users.map(u => u.posts) triggers N queries"
      solution: "Use eager loading: include: { posts: true }"
      source: "context7://prisma#eager-loading"
  
    # ARCHITECTURE - Entity Leakage
    - id: "ARCH-DTO-001"
      severity: high
      file: "src/api/users.ts:35"
      finding: "ORM entity returned directly from API endpoint"
      issue: "User entity with password hash exposed in GET /users response"
      fix: "Create UserResponseDTO, map entity → DTO before return"
  
    # ARCHITECTURE - Centralized Error Handling
    - id: "ARCH-CEH-001"
      severity: medium
      file: "src/app.ts"
      finding: "No global error handler registered"
      issue: "Unhandled exceptions return stack traces to client in production"
      fix: "Add app.use(globalErrorHandler) with sanitized error responses"
  
    # MAINTAINABILITY - God Class
    - id: "MNT-GOD-001"
      severity: medium
      file: "src/services/order-service.ts"
      finding: "God class with 22 methods and 680 lines"
      issue: "OrderService handles creation, payment, shipping, notifications"
      fix: "Extract PaymentService, ShippingService, NotificationService"
  
    # MAINTAINABILITY - Dead Code
    - id: "MNT-DC-001"
      severity: medium
      file: "src/auth/legacy-adapter.ts"
      finding: "Backward-compatibility wrapper kept after migration"
      dead_code: "legacyLogin() wraps newLogin() — callers already migrated"
      action: "Delete legacy-adapter.ts, remove re-export from index.ts"
  
    # MAINTAINABILITY - DRY
    - id: "MNT-DRY-001"
      severity: medium
      file: "src/service.ts:42"
      finding: "DRY violation: duplicate validation logic"
      suggested_action: "Extract to shared validator"
  

• Linear comment posted with findings.

Reference Files

• Code metrics: references/code_metrics.md (thresholds and penalties)
• Guides: docs/guides/
• Templates for context: shared/templates/task_template_implementation.md
• Clean code checklist: shared/references/clean_code_checklist.md

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Version: 5.0.0 Last Updated: 2026-01-29