Phoenix Context Boundary Validation skill

Phoenix Context Boundary Validation

Analyze module dependencies to ensure clean context separation and proper architectural boundaries.

Usage

/phx:boundaries              # Check for violations
/phx:boundaries --assess     # Score context health (0-100)
/phx:boundaries --fix        # Suggest fixes for violations

--assess Mode: Context Health Score

Evaluate overall boundary health with a quantified score.

Metrics Calculated

Metric	Healthy Range	Red Flag	Weight
Modules per context	3-15	>20 or <2	20%
Public API surface	5-30 funcs	>40 funcs	15%
Fan-out (contexts called)	1-4	>6	20%
Fan-in (called by contexts)	1-6	>10	15%
Circular dependencies	0	>0	15%
Boundary violations	0	>0	15%

Commands for Assessment

Use Glob to count .ex files per context directory under lib/my_app/*/. Use Grep to count public function definitions per context file under lib/my_app/*.ex. Run mix xref graph --format stats for dependency analysis. Run mix xref graph --format cycles --label compile for compile-time circular dependencies.

Output Format

## Context Health Assessment

### Overall Score: 82/100 (Good)

| Context | Modules | API | Fan-Out | Fan-In | Score |
|---------|---------|-----|---------|--------|-------|
| Accounts | 5 | 12 | 2 | 4 | 95 |
| Orders | 18 | 45 | 8 | 3 | 62 |
| Shared | 2 | 8 | 0 | 12 | 78 |

### Issues Found

1. **Orders** - Too large (18 modules, 45 funcs)
   - Consider: Extract Fulfillment, Invoicing sub-contexts

2. **Orders** - High fan-out (8 contexts)
   - Consider: Review if all dependencies necessary

### Recommendations

- Split Orders into Orders + Fulfillment
- Review Accounts ← Billing dependency

Iron Laws - Never Violate These

1. Controllers call only contexts - No direct Repo access from web layer
2. Schemas are pure data - No side effects, no Repo calls in schema modules
3. Contexts own their schemas - Don't import schemas from other contexts
4. Explicit dependencies only - Cross-context calls must be intentional
5. DO NOT refactor context boundaries without running mix xref first — Refactoring without dependency data creates new violations; always map the dependency graph before moving modules

Dependency Rules

Layer	Can Call	Cannot Call
Controllers	Contexts, Plug, Conn	Repo, Schemas directly
LiveViews	Contexts, Components, PubSub	Repo, Schemas directly
Contexts	Own schemas, Repo, other contexts	Web layer modules
Schemas	Ecto types, validations	Contexts, Repo

Analysis Commands

Check Compile Dependencies

Run mix xref graph --label compile-connected.

Find What Depends on a Context

Run mix xref graph --sink MyApp.Accounts --label compile.

Find What a Module Calls

Run mix xref callers MyApp.Accounts.get_user!/1.

Check for Circular Dependencies

Run mix xref graph --format cycles --label compile.

Red Flags to Detect

Issue	Detection Command	Fix
Repo in web layer	grep -r "Repo\." lib/my_app_web/	Move to context
Schema with queries	grep -r "import Ecto.Query" lib/my_app/**/schemas/	Move queries to context
Cross-context schema import	grep -r "alias MyApp.Other.Schema" lib/my_app/ctx/	Call context API
Business logic in LiveView	grep -r "Repo\.|Ecto\.Multi" lib/my_app_web/live/	Extract to context

Boundary Verification Process

1. Run mix xref graph --label compile-connected for overview
2. Check for context cross-contamination
3. Verify no direct Repo calls from web layer
4. Ensure schemas have no side effects
5. Validate explicit cross-context dependencies

Next Steps

Always end with actionable follow-up — findings without a plan get lost:

- `/phx:plan` — Create a plan to fix violations (recommended for 3+ issues)
- `/phx:quick` — Fix a single boundary violation directly
- `/phx:review` — Review specific modules for deeper issues

References

For detailed patterns, see:

• ${CLAUDE_SKILL_DIR}/references/context-design.md - Context design principles
• ${CLAUDE_SKILL_DIR}/references/refactoring-boundaries.md - Fixing boundary violations