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
Install the expert binary and make sure it's on your PATH. See installation instructions.
Note:
mix-format,mix-compile, andmix-credorequire bash (Git Bash or WSL on Windows).
Plugins
Overview
| Plugin | Type | Description |
|---|---|---|
| elixir-lsp | LSP | Language Server with completions, go-to-definition, diagnostics |
| 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 |
Tools
elixir-lsp
Elixir Language Server integration powered by Expert.
| Feature | Description |
|---|---|
| Navigation | Go to definition, find references |
| Completions | With signature help and docs |
| Diagnostics | Compiler warnings and errors |
| File types | .ex, .exs, .heex, .leex |
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
.exfiles (not.exsscripts/tests) - Finds
mix.exsby 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
.exand.exsfiles - Uses project's default Credo configuration
- Gracefully skips if Credo is not installed
- Fails on code quality issues
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
phoenix-thinking
Architectural patterns for Phoenix and LiveView.
| Concept | Insight |
|---|---|
| Where to load data | mount/3 by default; handle_params/3 for live navigation (push_patch) |
| Initial double-load | mount and handle_params both run twice; use connected?/1, assign_async/3, or assign_new/3 |
| Scopes (1.8+) | Security-first authorization threading |
| PubSub | Scoped topics, broadcast_from to avoid self-broadcast |
| Channel fastlane | Socket state can be stale — re-fetch or include in broadcast |
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
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
Known Issues
elixir-lsp: client/registerCapability workaround. Claude Code's LSP client doesn't respond to client/registerCapability requests that Expert sends during initialization (anthropics/claude-code#32595). The plugin includes a Python wrapper (expert-wrapper) that intercepts these requests and auto-responds so Expert can initialize properly. The wrapper will be removed once the upstream fix lands. Requires Python 3 on PATH.
Troubleshooting
expert not found: Ensure the expert binary is on your PATH. See installation instructions.
License
Copyright (c) 2025 George Guimarães
Licensed under the Apache License, Version 2.0. See LICENSE for details.