Development style guides

Editor/IDE styling standardization

We use EditorConfig to automatically apply certain styling standards before files are saved locally. Some editors and IDEs honor the .editorconfig settings automatically by default.

If your editor or IDE does not automatically support .editorconfig, we suggest investigating to see if a plugin exists. For example, a plugin for vim.

Pre-push static analysis with Lefthook

Lefthook is a Git hooks manager that allows custom logic to be executed prior to Git committing or pushing. GitLab comes with Lefthook configuration (lefthook.yml), but it must be installed.

We have a lefthook.yml checked in but it is ignored until Lefthook is installed.

Uninstall Overcommit

We were using Overcommit prior to Lefthook, so you may want to uninstall it first with overcommit --uninstall.

Install Lefthook

  1. You can install lefthook in different ways. If you do not choose to install it globally (for example, via Homebrew or package managers), and only want to use it for the GitLab project, you can install the Ruby gem via:

    bundle install
  2. Install Lefthook managed Git hooks:

    # If installed globally
    lefthook install
    # Or if installed via ruby gem
    bundle exec lefthook install
  3. Test Lefthook is working by running the Lefthook pre-push Git hook:

    # If installed globally
    lefthook run pre-push
    # Or if installed via ruby gem
    bundle exec lefthook run pre-push

This should return the Lefthook version and the list of executable commands with output.

Lefthook configuration

Lefthook is configured with a combination of:

Lefthook auto-fixing files

We have a custom lefthook target to run all the linters with auto-fix capabilities, but just on the files which changed in your branch.

# If installed globally
lefthook run auto-fix
# Or if installed via ruby gem
bundle exec lefthook run auto-fix

Disable Lefthook temporarily

To disable Lefthook temporarily, you can set the LEFTHOOK environment variable to 0. For instance:

LEFTHOOK=0 git push ...

Run Lefthook hooks manually

To run the pre-push Git hook, run:

bundle exec lefthook run pre-push

For more information, check out Lefthook documentation.

Skip Lefthook checks per tag

To skip some checks based on tags when pushing, you can set the LEFTHOOK_EXCLUDE environment variable. For instance:

LEFTHOOK_EXCLUDE=frontend,documentation git push ...

As an alternative, you can create lefthook-local.yml with this structure:

    - frontend
    - documentation

For more information, check out Lefthook documentation.

Skip or enable a specific Lefthook check

To skip or enable a check based on its name when pushing, you can add skip: true or skip: false to the lefthook-local.yml section for that hook. For instance, you might want to enable the gettext check to detect issues with locale/gitlab.pot:

      skip: false

For more information, check out Lefthook documentation Skipping commands section.

Database migrations

See the dedicated Database Migrations Style Guide.


See the dedicated JS Style Guide.


See the dedicated SCSS Style Guide.


See the dedicated Ruby Style Guide.


See the dedicated Go standards and style guidelines.

Shell commands (Ruby)

See the dedicated Guidelines for shell commands in the GitLab codebase.

Shell scripting

See the dedicated Shell scripting standards and style guidelines.


We’re following Ciro Santilli’s Markdown Style Guide.


See the dedicated Documentation Style Guide.

Guidelines for good practices

Good practice examples demonstrate encouraged ways of writing code while comparing with examples of practices to avoid. These examples are labeled as Bad or Good. In GitLab development guidelines, when presenting the cases, it’s recommended to follow a first-bad-then-good strategy. First demonstrate the Bad practice (how things could be done, which is often still working code), and then how things should be done better, using a Good example. This is typically an improved example of the same code.

Consider the following guidelines when offering examples:

  • First, offer the Bad example, and then the Good one.
  • When only one bad case and one good case is given, use the same code block.
  • When more than one bad case or one good case is offered, use separated code blocks for each. With many examples being presented, a clear separation helps the reader to go directly to the good part. Consider offering an explanation (for example, a comment, or a link to a resource) on why something is bad practice.
  • Better and best cases can be considered part of the good cases’ code block. In the same code block, precede each with comments: # Better and # Best.

Although the bad-then-good approach is acceptable for the GitLab development guidelines, do not use it for user documentation. For user documentation, use Do and Don’t. For examples, see the Pajamas Design System.


See the dedicated Python Development Guidelines.


Code should be written in US English.