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igmarin/elixir-phoenix-skills

Curated library of 38 atomic skills, 7 personas, and 1 orchestrator for Elixir and Phoenix development. Organized by category: fundamentals, phoenix, database, testing, auth, infrastructure, quality, security, integrations, tooling, frameworks, personas, and orchestration. Covers core Elixir patterns, Phoenix LiveView, Ecto, OTP, Oban, testing, security, deployment, real-time, and modern tooling (Req, Swoosh, Cachex, Broadway, Ash).

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Overview
Quality
Evals
Security
Files

SKILL.mdskills/quality/credo-config/

name:
credo-config
type:
atomic
tags:
atomic
license:
MIT
description:
MANDATORY for all code quality and linting work. Use when setting up or customizing Credo for Elixir projects, configuring .credo.exs, or adding Credo to CI pipelines. Generates .credo.exs configuration files, writes custom check modules, configures strictness levels, and integrates Credo into CI pipelines. Trigger words: Credo, .credo.exs, linting, code style, static analysis, custom checks, credo.config, mix credo, code quality, lint, static analysis, format check.
metadata:
{"user-invocable":"true","version":"1.0.0"}

Credo Configuration

RULES — Follow these with no exceptions

  1. Always run mix credo gen.config first — never hand-craft .credo.exs from scratch
  2. Use --strict in CI — enables additional checks that are disabled by default
  3. Add inline disables sparingly — document why each exception is necessary
  4. Custom checks belong in lib/credo/checks/ — never inline them in application code

Setup Workflow

Follow this sequence when setting up or customizing Credo:

1. Add Dependency

# mix.exs
defp deps do
  [
    {:credo, "~> 1.7", only: [:dev, :test], runtime: false}
  ]
end

2. Fetch Dependencies

mix deps.get

3. Generate Default Config

mix credo gen.config

4. Customize .credo.exs

Edit the generated file to match your project's needs. See Basic Configuration below.

5. Verify Setup

mix credo

Success: Credo exits 0 and prints a summary with issue counts per category. If issues are found, review them — fix violations, adjust check configuration, or add inline disable comments for intentional exceptions.

6. Run in Strict Mode

mix credo --strict

Strict mode enables additional checks disabled by default (mostly design-related). CI must use --strict.

7. Add to CI

See CI Integration below.

8. Create Custom Checks

For project-specific patterns, add custom check modules to lib/credo/checks/. See Custom Checks below.

Basic Configuration

Use mix credo gen.config for the complete check list rather than writing it by hand.

# .credo.exs
%{
  configs: [
    %{
      name: "default",
      strict: false,
      color: true,
      files: %{
        included: ["lib/", "src/", "test/", "web/", "apps/"],
        excluded: [~r"/_build/", ~r"/deps/", ~r"/node_modules/"]
      },
      checks: %{
        enabled: [
          {Credo.Check.Readability.MaxLineLength, [priority: :low, max_length: 120]},
          {Credo.Check.Design.AliasUsage, [if_nested_deeper_than: 2, if_called_more_often_than: 0]},
          # ... add or override checks as needed
        ],
        disabled: [
          {Credo.Check.Consistency.MultiAliasImportRequireUse, []},
          {Credo.Check.Design.DuplicatedCode, []},
        ]
      }
    },
    %{
      name: "strict",
      strict: true,
      files: %{
        included: ["lib/", "src/", "test/", "web/", "apps/"],
        excluded: [~r"/_build/", ~r"/deps/", ~r"/node_modules/"]
      },
      checks: %{
        enabled: [
          {Credo.Check.Design.TagTODO, [priority: :high]},
          {Credo.Check.Readability.Specs, []},
        ]
      }
    }
  ]
}

Disabling Checks

For a Single Line

# credo:disable-for-next-line
def my_function_with_long_name, do: :ok

def my_function, do: :ok # credo:disable-for-this-line

For a File

# At the top of the file
# credo:disable-for-this-file Credo.Check.Readability.ModuleDoc

defmodule MyApp.LegacyModule do
  # No module doc needed
end

In Configuration

# .credo.exs
checks: %{
  disabled: [
    {Credo.Check.Readability.ModuleDoc, []}
  ]
}

CI Integration

# .github/workflows/ci.yml
name: CI

on: [push, pull_request]

jobs:
  credo:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: erlef/setup-beam@v1
        with:
          elixir-version: '1.15'
          otp-version: '26.0'
      - run: mix deps.get
      - run: mix credo --strict

CI must use --strict to catch all issues. Exit code 0 means clean; non-zero means issues found.

Handling Failures in CI

When Credo fails in CI:

  1. Run locally: mix credo
  2. Review each category starting with Readability
  3. Fix the root cause — refactor function, extract logic, shorten names
  4. Only disable a check if it's a false positive with documentation

Mix Alias

# mix.exs
defp aliases do
  [
    "lint": ["credo --strict"],
    "quality": ["format --check-formatted", "credo --strict", "sobelow --config"]
  ]
end

Custom Checks

Create custom checks for project-specific patterns in three steps:

  1. Define a module using use Credo.Check in lib/credo/checks/.
  2. Implement run/2 with Credo.Code.prewalk/2 to traverse the AST and collect issues.
  3. Register the module under checks.enabled in .credo.exs.

The example below detects direct Repo. calls inside LiveView modules — adapt find_issues/3 to match your own patterns:

# lib/credo/checks/no_direct_repo_in_live_view.ex
defmodule Credo.Check.NoDirectRepoInLiveView do
  use Credo.Check, category: :design, base_priority: :high

  @explanation """
  LiveViews should not call Repo directly. Use context functions instead.
  """

  def run(%Credo.SourceFile{} = source_file, params) do
    issue_meta = IssueMeta.for(source_file, params)

    source_file
    |> Credo.Code.prewalk(&find_issues(&1, &2, issue_meta))
  end

  # Detect calls of the form MyApp.Repo.<any function>
  defp find_issues(
         {{:., _, [{:__aliases__, meta, [_, "Repo"]}, _fn]}, _, _} = ast,
         issues,
         issue_meta
       ) do
    issue = format_issue(issue_meta, message: "Avoid direct Repo calls in LiveViews.", line_no: meta[:line])
    {ast, [issue | issues]}
  end

  defp find_issues(ast, issues, _issue_meta), do: {ast, issues}
end

Register the custom check in .credo.exs:

checks: %{
  enabled: [
    {Credo.Check.NoDirectRepoInLiveView, []}
  ]
}

skills

quality

credo-config

SKILL.md

README.md

tile.json