⌘ K
dockerfile · uppercase instructions · live

Format Dockerfile instructions

Normalises instruction casing (FROM, RUN, CMD…) and collapses run-on whitespace. A quick tidy pass before committing the Dockerfile. Runs locally.

Dockerfile Formatter
Input
101 B
6 lines
Output
102 B
7 lines
Status
ready
live
Ratio
1.01×
out/in
input · dockerfile
output · formatted dockerfile
FROM node:20-alpine
WORKDIR /app
COPY package.json .
RUN npm install
COPY . .
CMD ["node","index.js"]
Quick Start

How to format a Dockerfile

Each known instruction (FROM, RUN, CMD, ENV, COPY…) is uppercased; the argument tail has redundant whitespace collapsed.

  1. 01

    Paste your Dockerfile

    Drop in any Dockerfile — multi-stage builds, ARG and ENV blocks all work.

    Parsing runs through Prettier’s standalone bundle (or the language-specific equivalent) loaded lazily — no parser ships until the tool is opened.

    dockerPrettierASTstandalonelazy
    input · sourceraw · AST
    from alpine
    loaded · parsedAST · ready
  2. 02

    Casing normalised

    Known instruction keywords get UPPERCASED; their arguments stay as-written.

    Indent width, tab style, and print-width re-format through a memoised pass — switching 2 → 4 spaces never re-parses, only re-prints.

    caseindentprint-widthmemoisedlive
    step · optionsinstr · live
    from → FROM
    options applied · livelive
  3. 03

    Whitespace tidied

    Multiple spaces in instruction tails collapse to single spaces; comments are preserved verbatim.

    The formatter is deterministic and idempotent: running it twice produces byte-identical output, which keeps diffs and git noise to a minimum.

    liveidempotentdeterministicdiff-cleanstable
    out · formattedtidy · ready
    RUN npm install
    formatted · liveidempotent
  4. 04

    Copy or download

    Drop the result back into your repo's Dockerfile or copy to clipboard.

    Download writes a Blob with the language-appropriate extension; copy uses navigator.clipboard.writeText so the output preserves all whitespace exactly.

    exportclipboardbloblanguage MIMEclient-side
    ok · copiedready · done
    ✓ Copied
    shipped · ready to shipsuccess
Pro tips

Formatting tips that keep diffs sane

Pick one config and pin it

Inconsistent formatting causes diff churn. Commit .prettierrc / .editorconfig and enforce in CI.

Format on save

Editor integration is faster feedback than a pre-commit hook. Use both for belt-and-braces.

Idempotency matters

Running the formatter twice should produce identical output. Test this on a representative file.

Match the language community

Default to community conventions: 2 spaces for JS/CSS, 4 for Python, tabs for Go. Fights over indent are a productivity tax.

Print-width drives wrapping

80, 100, and 120 are the common targets. Wider lines parse fast but review slower side-by-side.

Don’t mix formatters and linters

Prettier handles whitespace; ESLint handles correctness. Disable overlapping rules to avoid fight-club configs.

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Use Cases

When to format a Dockerfile

Repo cleanup, lint pre-pass, docs.

Repo cleanup

Normalise inherited Dockerfiles before adding to CI. Idempotent: running the formatter twice produces byte-identical output, which is the foundation of a clean CI gate. Pair with a pre-commit hook so PRs arrive already formatted, focusing review on logic.

idempotent

Lint pre-pass

Fix obvious casing issues before running hadolint. Pairs with EditorConfig + .prettierrc for end-to-end consistency. Whitespace-only changes vanish so reviewers see real diffs, and git blame stays honest about who wrote what.

CI-ready

Multi-stage builds

Make a long multi-stage Dockerfile readable for review. Output respects your indent width, tab style, and print-width — settings carry over for repeat runs. Switching 2-space to 4-space costs nothing in CPU but standardises an entire codebase.

diff-clean

Tutorial code

Standardise Dockerfiles in your team's onboarding docs. Format-on-save is the fastest feedback loop; CI is the safety net. Together they make inconsistent indentation a thing of the past and free up review cycles for genuine concerns.

PR-friendly

Quick share

Tidy a Dockerfile before pasting into chat or a gist. Whitespace-only changes don't trigger downstream content-hash invalidations, so CDN cache keys and CI cache layers stay warm. Real changes get all the rebuild budget.

review-ready

Docs examples

Make Dockerfile examples in technical docs consistent. Pairs with linters (ESLint, Stylelint, pylint) that catch what formatting alone can't — bugs, unused imports, dead code. Each tool stays in its lane, and the codebase stays clean.

deterministic
FAQ

Frequently asked questions

No — hadolint is a linter and reports issues. This formatter only normalises whitespace and instruction casing.
No. Order is preserved exactly; build cache behaviour is unchanged.
Trailing backslash continuations are kept as written; they're not joined or split.
Comment lines (#) are passed through unchanged.
No — the formatter runs locally in your browser tab.
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