elixir-mix-install-debug

name	elixir-mix-install-debug
description	Create and use Mix.install standalone scripts for debugging Elixir code, testing APIs, exploring libraries, and isolating problems. Use when you need to test third-party integrations, verify library behavior, debug signatures, or prototype solutions outside the main project.

Elixir Mix.install Debug Script Workflow

When to Use This Skill

Use standalone .exs debug scripts when you need to:

• Isolate API integration issues - Test API signatures, request formats, authentication
• Explore new libraries - Understand library APIs before integrating into main project
• Debug complex problems - Remove project dependencies to narrow down root cause
• Test multiple approaches - Compare different solutions side-by-side
• Verify fixes - Reproduce bugs in isolation before applying fixes to main codebase
• Prototype features - Quick proof-of-concept without modifying project

Don't use for:

• Unit tests (use ExUnit in test/ directory)
• Production code (belongs in lib/)
• Simple one-line checks (use iex instead)

Prerequisites

• Elixir 1.12+ (for Mix.install support)
• Project .env file with required credentials (if testing authenticated APIs)
• For Windows users: WSL or Git configured with core.autocrlf input

Instructions

Step 1: Identify What Needs Debugging

Ask yourself:

• What specific behavior am I trying to understand or fix?
• Can I isolate this from the rest of the project?
• What dependencies does this require?

Common scenarios:

• Third-party API returning unexpected errors
• Library behaving differently than documented
• Signature/authentication issues
• Response parsing problems
• Multimodal content handling (images, audio)

Step 2: Choose the Right Template

Select from templates/ based on your scenario:

Template	Use When	Example
basic.exs	Testing HTTP APIs, simple library functions	API client testing, signature debugging
liveview.exs	Testing Phoenix LiveView components interactively	Upload flows, form interactions
multimodal.exs	Working with images, audio, or other media	Vision APIs, content parsing
dotenv_loader.exs	Just the DotEnv module for custom scripts	Building your own script from scratch

Copy the template:

# From project root
cp .factory/skills/elixir-mix-install-debug/templates/basic.exs scripts/my_debug.exs

Step 3: Configure Dependencies

Edit the Mix.install/1 block in your script:

Mix.install([
  {:req, "~> 0.5"},           # From Hex.pm
  {:my_lib, "~> 1.0"},        # Add needed dependencies
  # {:local_lib, path: "../my_lib", override: true},  # Local testing
  # {:pr_lib, github: "user/repo", branch: "fix-123", override: true}  # Test PR
])

Common patterns:

• Use override: true when dependency conflicts arise
• Test GitHub branches before merging: github: "user/repo", branch: "feature"
• Test local changes: path: "../relative/path"

Step 4: Load Environment Variables

The templates include the DotEnv module that handles .env files:

DotEnv.load()  # Searches .env, ../.env, ../../.env

# Then access variables
api_key = System.get_env("API_KEY") || raise "API_KEY not set"

Tips:

• DotEnv gracefully handles missing files
• Add fallback values for non-sensitive defaults
• Mask sensitive values in debug output

Step 5: Structure Your Tests

Organize your script into clear sections:

# ============================================================================
# Configuration
# ============================================================================
config = %{
  api_key: System.get_env("API_KEY"),
  endpoint: "https://api.example.com"
}

IO.puts("=== Configuration ===")
IO.inspect(config, pretty: true)

# ============================================================================
# Test 1: Basic Request
# ============================================================================
IO.puts("\n=== Test 1: Basic Request ===")
# Test code...

# ============================================================================
# Test 2: With Parameters
# ============================================================================
IO.puts("\n=== Test 2: With Parameters ===")
# Test code...

Best practices:

• Print clear section headers
• Use IO.inspect/2 with labels for debugging
• Test one thing at a time
• Include both success and failure cases

Step 6: Run and Debug

Execute your script:

# Method 1: Direct execution (if script has shebang)
chmod +x scripts/my_debug.exs
./scripts/my_debug.exs

# Method 2: Via elixir command
elixir scripts/my_debug.exs

# Method 3: In WSL (for Windows users)
wsl -e bash -c "cd /mnt/f/path/to/project && elixir scripts/my_debug.exs"

Common issues:

Problem	Solution
Syntax errors with backslashes	Run mix format scripts/my_debug.exs to fix CRLF issues
"Module X not available"	Add missing dependency to Mix.install
Environment variable nil	Check DotEnv loaded before accessing, verify .env file exists
Dependency conflict	Add override: true to dependency spec

Step 7: Extract Learnings

Once you've isolated the problem:

1. Document the finding - Add comments to the script explaining what worked
2. Update main codebase - Apply the fix to your project code
3. Keep or delete script:
   • Keep if it's a reusable test (rename to xxx_demo.exs)
   • Delete if it was one-time debugging (cleanup test_*.exs)
4. Update documentation - Note the issue and solution in project docs

Script naming conventions:

• xxx_demo.exs - Reusable demonstrations/explorations (keep in repo)
• xxx_test.exs - Problem debugging/verification (can delete after)
• test_xxx.exs - Temporary debugging (clean up after solving)

Advanced Patterns

Testing Multiple Approaches

approaches = [
  {"Approach A", fn -> method_a() end},
  {"Approach B", fn -> method_b() end},
  {"Approach C", fn -> method_c() end}
]

Enum.each(approaches, fn {name, func} ->
  IO.puts("\n=== #{name} ===")
  case func.() do
    {:ok, result} -> IO.puts("✅ Success: #{inspect(result)}")
    {:error, reason} -> IO.puts("❌ Failed: #{inspect(reason)}")
  end
end)

Mock vs Real API Testing

From scripts/cot_debug.exs pattern:

mode = if System.get_env("API_KEY"), do: :real, else: :mock

case mode do
  :real -> run_real_api_call()
  :mock -> run_mock_simulation()
end

Generating curl Commands

Useful for comparing Elixir behavior with raw HTTP:

IO.puts("""
Test with curl:
curl -X POST '#{url}' \\
  -H 'Authorization: Bearer #{api_key}' \\
  -d '#{Jason.encode!(body)}'
""")

Verification

Before considering the script complete:

• Script runs without syntax errors
• All environment variables are loaded correctly
• Dependencies install successfully
• Test cases produce expected output
• Windows users: Run mix format scripts/my_debug.exs to fix line endings
• Sensitive data (API keys) are masked in output
• Script includes clear comments explaining the purpose

Examples from Project

Refer to these existing scripts for patterns:

• scripts/test_r2_delete.exs - Debugging AWS signature issues, includes curl output
• scripts/req_llm_pic_demo.exs - Multimodal API testing with ReqLLM
• scripts/s3_upload_demo.exs - Phoenix LiveView + external uploads with Buckets
• scripts/jido_demo.exs - Testing library from GitHub branch
• scripts/cot_debug.exs - Dual-mode (real/mock) testing with Phoenix Playground

Troubleshooting

Windows + WSL Issues

CRLF Line Endings:

# Fix with mix format
mix format scripts/my_debug.exs

# Or configure git globally
git config --global core.autocrlf input

Path Issues:

# Windows path: F:\Fcode\web\project
# WSL path: /mnt/f/Fcode/web/project

Dependency Issues

Conflict Resolution:

Mix.install([
  {:conflicting_lib, "~> 1.0", override: true}  # Force this version
])

Clear Cache:

rm -rf ~/.mix/installs/

Environment Loading

Debug DotEnv:

# Add debug output to DotEnv.load/1
IO.puts("🔍 Checking: .env, ../.env, ../../.env")
IO.puts("✅ Loaded: #{path}") # When found

Next Steps

After successfully debugging:

1. Apply findings to main codebase
2. Consider adding ExUnit tests for regression prevention
3. Update relevant documentation
4. Clean up temporary test scripts
5. Share learnings with team (commit demo scripts if valuable)

---

Tip: Keep valuable debug scripts in scripts/ directory and commit them to git. They serve as executable documentation and can be reused by teammates.