Claude Code Elixir

Claude Code plugins for Elixir development.

Installation

claude plugin marketplace add georgeguimaraes/claude-code-elixir

Install all plugins:

claude plugin install elixir-lsp@claude-code-elixir && \
claude plugin install mix-format@claude-code-elixir && \
claude plugin install mix-compile@claude-code-elixir && \
claude plugin install mix-credo@claude-code-elixir && \
claude plugin install elixir@claude-code-elixir

Prerequisites

Platform	Command
macOS	brew install elixir elixir-ls
Windows	choco install elixir elixir-ls
Any (mise)	mise use -g elixir-ls

Note: mix-format, mix-compile, and mix-credo require bash (Git Bash or WSL on Windows).

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Plugins

Overview

Plugin	Type	Description
elixir-lsp	LSP	Language Server with completions, go-to-definition, Dialyzer
mix-format	Hook	Auto-format .ex/.exs files on save
mix-compile	Hook	Compile with --warnings-as-errors on save
mix-credo	Hook	Run Credo code quality checks on save
elixir	Skills	BEAM architecture, Phoenix, Ecto, OTP patterns

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Tools

elixir-lsp

Elixir Language Server integration powered by elixir-ls.

Feature	Description
Navigation	Go to definition, find references
Completions	With signature help and docs
Diagnostics	Dialyzer type checking
File types	.ex, .exs, .heex, .leex

Default settings

Option	Default	Description
dialyzerEnabled	true	Enable Dialyzer diagnostics
fetchDeps	false	Auto-fetch deps on compile
suggestSpecs	true	Suggest @spec annotations

Override per-project: .elixir_ls/settings.json

mix-format

Auto-runs mix format after editing .ex and .exs files.

mix-compile

Auto-runs mix compile --warnings-as-errors after editing .ex files.

• Only .ex files (not .exs scripts/tests)
• Finds mix.exs by walking up directories
• Fails on warnings or errors

mix-credo

Auto-runs mix credo after editing .ex and .exs files to check code quality.

• Runs on both .ex and .exs files
• Uses project's default Credo configuration
• Gracefully skips if Credo is not installed
• Fails on code quality issues

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Skills

elixir

Paradigm-shifting skills for Elixir, Phoenix, and OTP development. Includes a SessionStart hook that auto-suggests skills when working on Elixir code.

Included skills:

Skill	Use When
elixir-thinking	Designing modules, processes, data structures
phoenix-thinking	Working with Phoenix, LiveView, PubSub
ecto-thinking	Working with Ecto, contexts, schemas
otp-thinking	Implementing GenServers, supervisors, Tasks

elixir-thinking

Mental models for writing Elixir — how it differs from OOP.

Concept	Insight
Iron Law	NO PROCESS WITHOUT A RUNTIME REASON
Three dimensions	Behavior, state, mutability are decoupled
Processes	For runtime (state/concurrency/faults), not code organization
"Let it crash"	Means "let it heal" — supervisors restart
Polymorphism	Behaviors → Protocols → Message passing (least to most dynamic)

Sources

• José Valim - Gang of None
• Saša Jurić - The Soul of Erlang and Elixir
• Saša Jurić - Clarity
• Designing Elixir Systems with OTP
• Official Elixir Guides

phoenix-thinking

Architectural patterns for Phoenix and LiveView.

Concept	Insight
Iron Law	NO DATABASE QUERIES IN MOUNT
Scopes (1.8+)	Security-first authorization threading
mount vs handle_params	mount = setup, handle_params = data
PubSub	Scoped topics, broadcast_from to avoid self-broadcast
Channel fastlane	Socket state can be stale — re-fetch or include in broadcast

Sources

• Phoenix 1.8 Scopes
• Phoenix LiveView Docs
• Stephen Bussey - Real-Time Phoenix

ecto-thinking

Architectural patterns for Ecto and contexts.

Concept	Insight
Contexts	Bounded domains with their own "dialect"
Cross-context refs	Use IDs, not belongs_to associations
Schemas	Multiple changesets per schema, embedded_schema for forms
Preloads	Separate vs join — pick based on data shape
pool_count vs pool_size	pool_count = DBConnection pools, pool_size = connections per pool

Sources

• Phoenix Contexts Guide
• German Velasco - DDD for Phoenix Contexts (ElixirConf 2024)
• Ecto Multi-Tenancy Guide

otp-thinking

OTP design patterns and when to use each abstraction.

Concept	Insight
Iron Law	GENSERVER IS A BOTTLENECK BY DESIGN
ETS	Bypasses bottleneck — concurrent reads with :read_concurrency
Task.Supervisor	THE pattern for async work (not raw Task.async)
Registry + DynamicSupervisor	Named dynamic processes without atom leaks
Broadway vs Oban	External queues vs background jobs — different problems

Sources

• Erlang OTP Design Principles
• Elixir GenServer Docs
• Elixir School - OTP Concurrency
• Saša Jurić - Elixir in Action
• Stephen Bussey - Real-Time Phoenix

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Troubleshooting

elixir-ls not found: Ensure Homebrew bin is in PATH:

export PATH="/opt/homebrew/bin:$PATH"

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License

Copyright (c) 2025 George Guimarães

Licensed under the Apache License, Version 2.0. See LICENSE for details.