Dockerfile Validator

Paste a Dockerfile and get an instant structural check plus best-practice lints — the same issues a reviewer flags: a misspelled or out-of-order instruction, a mutable base tag, a missing HEALTHCHECK, or running as root. It runs entirely in your browser.

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FROM node:20-alpine AS build
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

FROM nginx:1.27-alpine
COPY --from=build /app/dist /usr/share/nginx/html
EXPOSE 80
HEALTHCHECK CMD wget -qO- http://localhost/ || exit 1
USER nginx
CMD ["nginx", "-g", "daemon off;"]

What it checks

• Unknown instructions and FROM ordering (only ARG may precede FROM).
• Mutable base tags (:latest or no tag).
• Multiple CMD/ENTRYPOINT (only the last wins) and deprecated MAINTAINER.
• apt-get without --no-install-recommends or list cleanup.
• ADD vs COPY, root user, and missing HEALTHCHECK.

Handles line continuations and multi-stage builds. For exhaustive rules, also run hadolint in CI.

Dockerfile Validator

What it checks

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