dockerfmt

name	dockerfmt
description	Use this skill when the user wants to format Dockerfiles, check Dockerfile formatting, or apply consistent style to Docker build files.

dockerfmt Plugin

Modern Dockerfile formatter written in Go. Format Dockerfiles with configurable indentation, trailing newlines, and redirect spacing. Compatible with pre-commit hooks and CI pipelines.

Commands

Formatting

• dockerfmt format file — Format Dockerfile(s)

Utility

• dockerfmt self version — Print dockerfmt version
• dockerfmt _ _ — Passthrough to dockerfmt CLI

Usage Examples

• "Format this Dockerfile"
• "Check if all Dockerfiles are properly formatted"
• "Format all Dockerfiles in the project"
• "Apply consistent indentation to Dockerfiles"

Installation

go install github.com/reteps/dockerfmt@latest

Or use the Docker image:

docker run --rm -v $(pwd):/data reteps/dockerfmt Dockerfile

Examples

# Format a Dockerfile and print to stdout
dockerfmt format file Dockerfile

# Format in place (overwrite the file)
dockerfmt format file Dockerfile -w

# Format multiple Dockerfiles in place
dockerfmt format file Dockerfile.dev Dockerfile.prod -w

# Check if a Dockerfile is already formatted (CI-friendly)
dockerfmt format file Dockerfile -c

# Read from stdin and format
cat Dockerfile | dockerfmt _ _

# Format with 2-space indentation
dockerfmt format file Dockerfile -w -i 2

# Add trailing newline
dockerfmt format file Dockerfile -w -n

# Add spaces after redirect operators
dockerfmt format file Dockerfile -w -s

# Combine options: indent 2, newline, space redirects
dockerfmt format file Dockerfile -w -i 2 -n -s

Key Features

• Fast formatting — Written in Go for speed
• In-place editing — -w flag to overwrite files
• CI-friendly checking — -c flag exits non-zero if not formatted
• Configurable indentation — -i flag for custom tab size (default: 4)
• Trailing newline — -n flag to end files with a newline
• Redirect spacing — -s flag for spaces after redirect operators
• Pre-commit compatible — Works with pre-commit hooks
• Docker image available — Run without installing locally
• EditorConfig support — Respects EditorConfig settings

Notes

• dockerfmt is a modern alternative to dockfmt
• Supports ignoring directives via comments in Dockerfiles
• Use -c in CI pipelines to enforce formatting without modifying files
• The formatter respects existing Dockerfile structure while applying consistent style
• Shell completions are available via dockerfmt completion <shell>