Credo for Elixir: mix credo, editor plugins, and the gaps

The dependency tuple keeps Credo out of the artifact you deploy

Credo is added the way any Mix dependency is added, and the dependency tuple is where the decisions sit:

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

Then two commands, one to fetch the package, one to run the analysis:

mix deps.get
mix credo

Three parts of that tuple shape everything downstream. `only: [:dev, :test]` keeps Credo out of the `:prod` dependency set, `runtime: false` leaves it out of the release boot path, and `~> 1.7` allows any 1.x release from 1.7 on, so a future 2.x means editing mix.exs rather than bumping a lock. The consequence for a team is scope. Credo is a thing you run on a workstation and inside a test suite. The example keeps it out of the production dependency set; run the task before deployment in development or CI, then fix findings in source and deploy the corrected application.

Strict analysis, file selection and JSON output

Run `mix credo` for the default report, or `mix credo --strict` to include lower-priority issues. The official guide also documents file and line arguments and JSON output, such as `mix credo lib/example.ex:12 --format json`. For CI, consult the suggest command documentation for exit-status and filtering options, and test the configured checks against your pipeline.

It shows refactoring chances and leaves every edit to you

Every verb in Credo's own description of itself is a verb of reporting. It shows refactoring opportunities, points at complex code fragments, warns about common mistakes, and surfaces inconsistencies in a naming scheme. Nothing on the project page describes a command that rewrites a file, applies a suggestion, or renames an identifier, so the cleanup cost is human time and it scales with the number of warnings you agree to act on. On a codebase carrying a few years of naming drift, the naming and complexity reports are where the volume sits, and no documented workflow shortens that first pass. You also have to write your own stopping rule, because a report that keeps growing after every commit is easy to stop opening by the third week.

Generate and adjust a Credo configuration

Credo reads configuration from `.credo.exs` in the project root or `config/`. Run `mix credo gen.config` to generate a complete example, then adjust the included files, enabled checks and strictness to fit the project. `mix credo info --verbose` shows which checks are enabled under the current configuration.

Six editor integrations, none pinned to a Credo release

Inline feedback comes from six integrations listed on the project page: IntelliJ Elixir for the JetBrains family of editors, linter-elixir-credo for Atom by @smeevil, Elixir Linter (Credo) for VSCode by @pantajoe, flycheck for Emacs, a Kakoune lint config, and Neovim through the null-ls diagnostics builtin. Each one lives in a different repository, and no version is attached to any of them, so nothing tells you which Credo release a given plugin last met. The consequence is the one that comes with linter bridges living out of tree: when a release changes output shape or check names, the plugin lags, and the repair lands somewhere other than this repository. The Atom package and the Kakoune config are tied to editors whose own extension lifetimes you do not control either.

Running Credo in a CI pipeline

Credo can run non-interactively in a build: install the Mix dependencies and run `mix credo` or `mix credo --strict` as a CI step. Its command documentation lists output formats, file filters and `--mute-exit-status`, which forces a zero status even when issues are found. Select flags deliberately and verify the behaviour on a known failing example before relying on the gate.

Tags trail master by months, and new checks come in through a fork

Maintenance is readable straight off the release list: v1.7.17 on 2026-03-03, v1.7.18 on 2026-04-10, and v1.7.19 on 2026-06-05, while the last push is dated 2026-10-21. The newest tag in that list therefore sits more than four months behind the tip of the default branch, so pinning to v1.7.19 gives you June behaviour and master may differ. Adding a check goes through the plain fork flow the page spells out:

git checkout -b my-new-feature
git commit -am 'Add some feature'
git push origin my-new-feature

The root shows where a change lands: `.template.check.ex`, `.template.debug.html`, `config/`, `lib/` and `test/`, next to `CHANGELOG.md`, `RELEASING.md`, `CONTRIBUTING.md` and `ISSUE_TEMPLATE.md`, with `.tool-versions` and `.devcontainer/` holding the toolchain the maintainers work in. What the two template files generate is not explained on the project page.

Editorial conclusion

Adopt Credo when an Elixir team wants naming and complexity feedback while writing code or in CI. Its documented options include strict analysis and JSON output, and `mix credo gen.config` creates an example configuration. Credo reports issues for developers to review and fix. Before pinning a version, confirm your editor plugin has caught up with that release, since the bridges live outside this repository.

Frequently asked questions

Official sources

1. License: MIT
2. Project website
3. README
4. Releases
5. rrrene/credo on GitHub