Phx Boundaries Skill for Claude

Phoenix Context Boundary Validation

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

Usage

$elixir-phoenix:phx-boundaries              # Check for violations
$elixir-phoenix:phx-boundaries --assess     # Score context health (0-100)
$elixir-phoenix: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

• Controllers call only contexts - No direct Repo access from web layer
• Schemas are pure data - No side effects, no Repo calls in schema modules
• Contexts own their schemas - Don't import schemas from other contexts
• Explicit dependencies only - Cross-context calls must be intentional
• 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

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

Next Steps

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

get lost:

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

References

For detailed patterns, see:

• references/context-design.md - Context design principles
• references/refactoring-boundaries.md - Fixing boundary violations