# Dockerfile Linter & Best-Practices Checker Hadolint-style static analysis for Dockerfiles without a Docker daemon: 30+ rules across image pinning, package-manager hygiene, layer caching, secrets and signal handling, with severities, line numbers and fix examples. > Canonical page: https://elysiatools.com/en/tools/dockerfile-linter - **Category:** Development - **Keywords:** dockerfile, hadolint, linter, docker best practices, container image ## Overview Rule IDs and severities mirror Hadolint v2.15 (DL4000 MAINTAINER=error, DL3025 shell-form CMD=warning, DL3057 HEALTHCHECK=info/optional). The parser handles the # escape= directive, line continuations, BuildKit heredocs, JSON-array form, multi-stage state resets per FROM, and # hadolint ignore=DLxxxx suppressions. BP001 is a platform best-practice extension reminding about .dockerignore on whole-context COPY. ## Inputs - **Dockerfile content** (textarea): FROM node:20-alpine WORKDIR /app COPY . . RUN npm ci --omit=dev CMD \["node", "server.js"\] - **Minimum severity shown** (select) - **Include HEALTHCHECK rule (DL3057)** (checkbox) ## When to use - Before committing or merging a new or changed Dockerfile. - When an existing recipe still uses :latest, MAINTAINER, sudo or unpinned packages. - To confirm a multi-stage production image uses a pinned base, non-root USER, JSON-form CMD and HEALTHCHECK. ## How it works - Paste the complete Dockerfile; the parser understands # escape=, line continuations, BuildKit heredocs, JSON-array instructions, multi-stage FROM resets and # hadolint ignore comments. - Optionally raise the minimum severity (info, warning or error) and toggle the HEALTHCHECK rule (DL3057). - Every matching rule is listed with its Hadolint-style ID, line, explanation and suggested correction, plus the BP001 reminder for whole-context COPY. - Results render as an HTML summary that counts errors, warnings and info findings. ## Use cases - Surface classic anti-patterns such as unpinned tags, leftover MAINTAINER, apt-get without cleanup and secrets in ENV. - Validate a multi-stage Node or Alpine production build for pinning, non-root USER and exec-form CMD. - Receive a line-level reminder to add a .dockerignore when the recipe copies the entire build context. ## Frequently asked questions ### Do I need Docker installed? No. Analysis is purely static and runs on the pasted text alone. ### Which rules are checked? More than 30 rules that mirror Hadolint v2.15 (DL4000, DL3007, DL3025, DL3057 and others) plus the platform extension BP001 for .dockerignore. ### How do I hide informational findings? Set Minimum severity shown to “Warnings and errors only” or “Errors only”. ### Can I suppress a rule on one line? Yes. Add a comment # hadolint ignore=DLxxxx (or a comma-separated list) on the instruction. ### Is the HEALTHCHECK check always on? 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