Dockerfmt

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>