Elixir Skills Awareness

When working on Elixir, Phoenix, or OTP code, check if any of these skills apply before writing code.

Available Skills

elixir-architectural-thinking

Use when: Designing modules, processes, data structures, or making architectural decisions in Elixir.

Covers:

• The fundamental paradigm shift: "You don't need a process" (processes are for runtime, not code organization)
• Functional core / imperative shell pattern
• "Let it crash" actually means "let it heal" (supervisors restart)
• Data transformation vs state management
• The three decoupled dimensions: behavior (modules), state (data), mutability (processes)
• Polymorphism mechanisms: behaviors, protocols, message passing
• Design patterns in Elixir (from José Valim's "Gang of None?" talk)
• Testing behavior, not implementation (unit = behavior, not code)
• Library author guidelines (avoid global config, provide child_spec)
• Pre-coding checklist: domain, data, process architecture, APIs, failure modes

Trigger phrases: "design", "architecture", "should I use a process", "how to structure", "pattern", "module organization", "testing strategy"

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phoenix-ecto-thinking

Use when: Working with Phoenix controllers, LiveView, contexts, Ecto schemas, or database patterns.

Covers:

• Phoenix Scopes (1.8): security-first authorization threading, multi-tenancy
• Contexts as bounded domains with their own "dialect"
• Cross-context references: use IDs, not belongs_to associations
• Ecto schemas: embedded_schema for forms, virtual fields, schemaless changesets, multiple changesets per schema
• Preload strategies: separate vs join preloads, N+1 prevention
• Multi-tenancy with composite foreign keys and prepare_query/3
• LiveView lifecycle: mount (setup only) vs handle_params (data queries)
• Stateful vs functional components
• PubSub patterns: scoped topics, broadcast_from to avoid self-broadcast
• External data polling: GenServer + PubSub, not LiveView polling
• DDD concepts for better contexts (from German Velasco's talk)

Trigger phrases: "LiveView", "context", "schema", "Ecto", "Phoenix", "preload", "PubSub", "multi-tenant", "scope", "mount", "handle_params"

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otp-thinking

Use when: Implementing GenServers, supervisors, Tasks, or deciding which OTP abstraction to use.

Covers:

• GenServer is a bottleneck BY DESIGN (processes one message at a time)
• When GenServer becomes a problem: mailbox filling, timeouts, degradation
• ETS pattern for bypassing GenServer bottleneck (concurrent reads)
• Decision tree: Agent vs GenServer vs Task vs plain functions
• GenStateMachine for explicit state machines with timeouts
• Supervision strategies: one_for_one, one_for_all, rest_for_one
• DynamicSupervisor for dynamic children, PartitionSupervisor for scaling
• Task.Supervisor.async is THE recommended pattern (not raw Task.async)
• Registry + DynamicSupervisor pattern for named dynamic processes
• Distributed OTP: Horde, :pg for cluster-wide process groups
• Broadway vs Oban: external queues vs background jobs (different problems)
• Telemetry for observability
• Debugging with :sys module

Trigger phrases: "GenServer", "supervisor", "Task", "process", "ETS", "bottleneck", "distributed", "Broadway", "Oban", "pool", "concurrent"

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How to Use

When you recognize trigger phrases or contexts above, invoke the skill:

Skill tool: elixir-architectural-thinking
Skill tool: phoenix-ecto-thinking
Skill tool: otp-thinking

The skill content will guide your approach before writing code.