Don't like ads? Go Ad-Free Today 

Dockerfile Linter & Formatter

Developer

ADVERTISEMENT · REMOVE?

INPUT

OUTPUT

Client Side

ADVERTISEMENT · REMOVE?

Guide

Dockerfile Linter & Formatter

Lint and format your Dockerfiles with best-practice rules inspired by hadolint. Check for security issues, optimize layers, enforce conventions, and format consistently — all in the browser.

How to Use

Paste your Dockerfile into the Linter tab to scan for errors, warnings, and optimization opportunities. Each issue shows the line number, severity level, and an explanation. Switch to the Formatter tab to apply consistent formatting with uppercase instructions, combined RUN commands, and clean spacing.

Features

Best Practice Linting – 50+ rules covering security, layer optimization, and Docker conventions
Severity Levels – Error, warning, and info classifications with detailed explanations
Security Scanning – Detect hardcoded secrets, root user, unpinned base images, and more
Layer Optimization – Suggestions to minimize layers and improve build caching
Consistent Formatting – Uppercase instructions, combined RUN commands, sorted arguments
Syntax Highlighting – Color-coded Dockerfile display in both tabs
Sample Dockerfile – Quick test with a pre-filled example

ADVERTISEMENT · REMOVE?

 FAQ

What is a Dockerfile and how does Docker use it?

A Dockerfile is a text file containing a sequence of instructions that Docker uses to build a container image. Each instruction (FROM, RUN, COPY, CMD, etc.) creates a new layer in the image. Docker reads the Dockerfile top to bottom, executing each instruction to assemble the final image. The layered architecture allows Docker to cache unchanged layers, making rebuilds faster. A well-written Dockerfile produces smaller, more secure, and more efficient container images.
Why should RUN commands be combined in Dockerfiles?

Each RUN instruction creates a new image layer. When you install packages across multiple RUN commands, earlier layers retain the package manager cache even if a later RUN deletes it — layers are immutable once created. Combining commands with && into a single RUN reduces the total number of layers and allows cleanup (like rm -rf /var/lib/apt/lists/*) to actually reduce image size. This is one of the most impactful optimizations for Docker image size.
What are multi-stage builds and when should you use them?

Multi-stage builds use multiple FROM statements in a single Dockerfile. Each FROM starts a new build stage with its own base image. You can copy artifacts from earlier stages into later ones using COPY --from=stage_name. This lets you use a full SDK image for compilation but ship only the compiled binary in a minimal runtime image. The result is dramatically smaller production images — a Go application might build in a 1GB SDK image but deploy in a 10MB scratch image.