elixir-expert-lsp

elixir-expert-lsp — Elixir Code Intelligence for Claude Code

A Claude Code plugin that connects Expert LSP — the official unified Elixir language server — to give Claude real-time code intelligence while working on Elixir projects.

What Claude gains

• Auto-diagnostics: After every file edit, Expert analyzes changes and reports errors, warnings, and missing imports. Claude sees issues immediately and fixes them in the same turn.
• Code navigation: Go to definition, find references, hover for type info, list symbols, code actions — precise navigation instead of grep-based search.

Verified capabilities

Capability	Status
File change sync	Yes
Code completion	Yes
Hover / type info	Yes
Go to definition	Yes
Find references	Yes
Document symbols	Yes
Workspace symbols	Yes
Code actions (quick fixes)	Yes
Code lens	Yes
Formatting	Yes
Execute commands	Yes

Performance Notes

Tested against an Elixir project (Rig, 8 lib files). Results are from a single project and may vary based on project size, hardware, and Expert version:

Metric	Expert LSP	ElixirLS v0.30.0
Project compile	12s	30s
Diagnostic latency	1.0s	Did not return diagnostics in test window
Incremental recompile	58ms	N/A

In this test, Expert detected an undefined function run/3 error within 1 second of saving. ElixirLS did not return diagnostics within the test window. Expert is in release candidate status; ElixirLS is more mature. Your results will vary.

First Run

On first use, Expert builds an analysis engine (~30 seconds). This is a one-time cost cached at ~/Library/Caches/expert/. Subsequent starts take under 1 second.

To warm the cache before using in Claude Code:

cd your-project
expert --stdio
# Wait until you see "Engine initialized" in .expert/expert.log (~30s)
# Then Ctrl+C

Each project also needs an initial compile on first open (~5-10s with warm engine). After that, incremental recompiles take milliseconds.

Requirements

• Claude Code v1.0.33+
• Expert LSP v0.1.0-rc.6+ installed and in your $PATH
• Elixir 1.15+ with OTP 26+ (check with elixir --version)

Install the plugin

# From the Claude Code CLI
claude plugin install elixir-expert-lsp@<marketplace>

# Or load locally for development
claude --plugin-dir /path/to/expert-lsp

Install Expert LSP

The plugin configures the connection but doesn't include the server binary. Install Expert using one of these methods:

Download pre-built binary (recommended)

Download the latest release for your platform from github.com/elixir-lang/expert/releases and place it in your $PATH:

# macOS ARM (Apple Silicon)
gh release download v0.1.0-rc.6 --pattern 'expert_darwin_arm64' --repo elixir-lang/expert --dir /tmp
cp /tmp/expert_darwin_arm64 ~/.local/bin/expert
chmod +x ~/.local/bin/expert

# macOS Intel
gh release download v0.1.0-rc.6 --pattern 'expert_darwin_amd64' --repo elixir-lang/expert --dir /tmp
cp /tmp/expert_darwin_amd64 ~/.local/bin/expert
chmod +x ~/.local/bin/expert

# Linux
gh release download v0.1.0-rc.6 --pattern 'expert_linux_amd64' --repo elixir-lang/expert --dir /tmp
cp /tmp/expert_linux_amd64 ~/.local/bin/expert
chmod +x ~/.local/bin/expert

Nightly builds

gh release download nightly --pattern 'expert_darwin_arm64' --repo elixir-lang/expert --dir /tmp
cp /tmp/expert_darwin_arm64 ~/.local/bin/expert
chmod +x ~/.local/bin/expert

Verify installation

expert --version
# Should output: 0.1.0-rc.6 (or newer)

Make sure ~/.local/bin is in your $PATH. Add this to your ~/.zshrc if needed:

export PATH="$HOME/.local/bin:$PATH"

Supported file types

Extension	Language ID
.ex	elixir
.exs	elixir
.heex	phoenix-heex
.leex	elixir

How it works

This plugin provides an .lsp.json configuration that tells Claude Code how to connect to Expert via stdio transport. Expert runs as a subprocess spawned by Claude Code, analyzing your project files and providing real-time diagnostics and navigation.

When you edit an Elixir file, Expert analyzes the changes and pushes diagnostics back to Claude Code. Claude sees type errors, missing imports, and compilation warnings immediately and can fix them in the same turn — without you running mix compile manually.

Expert LSP vs ElixirLS

Expert is the official unified Elixir language server, created by the Elixir core team by merging the three previous implementations (ElixirLS, Lexical, Next LS). It's built on the Lexical codebase with Next LS components for single-binary releases and protocol abstraction.