What is Dockerfile Linter?
A comprehensive online linting tool that analyzes your Dockerfiles for best practices, security vulnerabilities, and optimization opportunities. This linter checks your Dockerfile against industry standards, Docker official recommendations, and common anti-patterns to help you build better, more secure container images.
The tool performs real-time analysis as you type, identifying issues like using latest tags, running as root, improper layer caching, missing version pinning, and inefficient RUN commands. It categorizes issues by severity (errors, warnings, info) and provides actionable recommendations for each finding. All analysis happens client-side in your browser for complete privacy.
Why Use Dockerfile Linter?
Manual Dockerfile review is time-consuming and easy to miss critical security or optimization issues. This linter automates best practice enforcement, catches common mistakes before they reach production, and helps teams maintain consistent Dockerfile standards. It's especially valuable for catching security issues like running as root, using vulnerable base images, or exposing sensitive information.
DevOps teams use this tool in their CI/CD pipelines to enforce standards, developers use it to learn Docker best practices, and security teams use it to identify potential vulnerabilities before deployment. The instant feedback helps you iterate faster and build production-ready images with confidence.
Common Use Cases
Security Audits: Scan Dockerfiles for security issues like running as root, using latest tags, missing USER instructions, or improper secret handling before deploying to production.
Build Optimization: Identify opportunities to reduce image size by combining RUN commands, using Alpine base images, cleaning up package managers, and optimizing layer caching.
Team Standards: Enforce consistent Dockerfile practices across your organization by checking for proper WORKDIR usage, label conventions, and multi-stage build patterns.
Learning Tool: Understand Docker best practices by seeing real-time explanations and recommendations for each issue found in your Dockerfile.
CI/CD Integration: Validate Dockerfiles automatically in your build pipeline to catch issues early before they impact production deployments.
How to Use Dockerfile Linter
Paste your complete Dockerfile into the editor and click 'Lint Dockerfile' to run the analysis. The tool will scan each instruction and display issues organized by severity level - errors (critical issues), warnings (recommended fixes), and info (optimization suggestions). Each issue shows the line number, description, and specific recommendations for fixing it.
The linter checks for over 20 different best practices including base image selection, layer optimization, security configurations, and metadata completeness. Results are color-coded by severity and include actionable advice like suggesting Alpine alternatives, recommending USER instructions, or showing how to combine RUN commands. You can fix issues iteratively and re-lint to verify your changes.
Frequently Asked Questions
Q: What Dockerfile best practices does it check? A: The linter checks for: version pinning (avoiding :latest), security (USER instruction, root usage), optimization (combining RUN commands, Alpine images, apt cleanup), proper instruction usage (COPY vs ADD, WORKDIR), metadata (LABEL, EXPOSE), and multi-stage build patterns.
Q: Can it auto-fix issues? A: Currently, the tool provides detailed recommendations for each issue but doesn't auto-fix. We show you exactly what to change with code examples and explanations so you understand the fixes.
Q: Does it support multi-stage builds? A: Yes, the linter understands multi-stage Dockerfile syntax and will analyze each stage separately, checking for proper stage naming, efficient COPY --from usage, and build context optimization.
Q: Is my Dockerfile data secure? A: Absolutely. All linting happens entirely in your browser using JavaScript. Your Dockerfile is never uploaded to any server, stored, or logged anywhere. It's completely private and secure.
Q: What severity levels are used? A: Errors (red) are critical issues that could cause security problems or build failures. Warnings (yellow) are strongly recommended fixes for best practices. Info (blue) are optimization suggestions that can improve your images.
Q: Can I use this in CI/CD? A: While this is a browser tool, the same linting rules can be implemented in CI/CD using tools like hadolint or dockerfile-lint. Use our tool for interactive development and learning.