elixir-phoenix-guide

Use when a form or operation manages parent and child records together — cast_assoc/cast_embed, on_replace, Ecto.Multi across tables, FK cascade design.

Use when writing GenServer, Supervisor, Task, Agent, or Registry code — init/handle_continue, call vs cast, supervision strategies, process naming.

Use when defining schemas, writing queries, or creating migrations — schema design, Repo usage, indexes, query composition.

Use when writing or refactoring core Elixir — pattern matching, case/cond/with, pipes, {:ok, _}/{:error, _} contracts. Baseline style for any .ex/.exs change not covered by a more specific skill.

Use when writing LiveView modules or HEEx templates — mount/handle_params lifecycle, assigns, streams, events, components.

Use when adding logging, metrics, or instrumentation — structured Logger usage, telemetry handler attachment, Ecto/Phoenix telemetry events.

Use when refactoring for duplication, complexity, or dead code — includes the plugin's on-demand analysis scripts.

Use when preparing releases or deployment config — runtime.exs vs compile-time config, release migrations, PHX_HOST/PHX_SERVER, assets, health checks.

Use when a resource needs multiple changesets (registration vs update), conditional validation, field transforms, or uniqueness validation — changeset composition.

Use when writing background jobs with Oban — worker options, return contracts, idempotency, uniqueness, Oban.Testing.

Use when extending phx.gen.auth — adding registration fields, custom user attributes, extra migrations alongside generated auth, fixture updates.

Use when deciding who may do what — ownership checks, policy modules, scoped queries, role-based access in LiveViews and controllers.

Use when building WebSocket features with Phoenix Channels — socket auth, join authorization, handle_in/push/broadcast, Presence.

Use when building JSON API endpoints — :api pipeline, FallbackController, error rendering, pagination, versioning, Bearer auth.

Use when protecting LiveViews with authentication — on_mount hooks, live_session, mount_current_scope, auth redirect testing.

Use when adding real-time updates via Phoenix.PubSub — subscribe/broadcast topology, topic naming, handle_info message handling.

Use when implementing file uploads — allow_upload, consume_uploaded_entries, validation, dev vs production storage (local, S3/:external), serving files.

Use when code touches user input, tokens, redirects, raw SQL, or logging — injection, XSS, atom exhaustion, timing attacks, audit tooling.

Use when writing or fixing ExUnit tests — case templates, async safety, fixtures, LiveView test helpers, error-path coverage.