Does this build the image?

No, it only performs static analysis on the text you paste.

What issues are checked?

Base image pinning, USER, HEALTHCHECK, ADD vs COPY, apt/apk cache cleanup, exec form CMD/ENTRYPOINT, and more.

Is my Dockerfile uploaded anywhere?

No, everything runs locally in your browser.

Does it work offline and on mobile?

Yes. Once the page has loaded it keeps working without a network connection, and the layout is responsive so it stays usable on phones and tablets.

Do I need an account or an API key?

No. Every tool on Coders Hub is free to use with no sign-up, no API key and no usage limits.

Dockerfile Linter

Lint a Dockerfile for common best-practice issues.

Support

Works Offline

Privacy First

No Login

No API

Dockerfile

Paste your Dockerfile contents

Findings

Static best-practice checks

Errors

Warnings

Info

L3 Copying the whole context (`COPY . .`) early can invalidate the Docker layer cache — copy dependency manifests first.
L5 Prefer exec form `CMD ["executable", "arg"]` over shell form for proper signal handling.
General No USER instruction found — the container will run as root by default.
General No HEALTHCHECK instruction — consider adding one for orchestrators to monitor container health.

About the Dockerfile Linter

Paste a Dockerfile and get instant feedback on common issues: unpinned base images, missing USER instruction, shell-form CMD/ENTRYPOINT, apt-get cache hygiene, and more.

Examples

Unpinned image

FROM node:latest

Output

Warning: avoid latest tag

Keyboard shortcuts

Copy the main outputCtrl / ⌘ + Shift + C
Download the resultCtrl / ⌘ + S
Share this toolCtrl / ⌘ + Shift + S
Reset the inputsAlt + R
Open the tool search paletteCtrl / ⌘ + K

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Frequently asked questions

Version 1.0.0 · Updated 2026-08-06 · Runs entirely in your browser