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About Online Elm Code Formatter

Elm code looks best when everyone uses the same style. This Elm Formatter wraps elm-format 0.19 so you can paste a module, hit Format, and get the exact canonical layout used by the Elm community. No custom style knobs, no arguments—just the standard Elm way of formatting.

Features of the Elm Formatter

  • Uses elm-format 0.19 under the hood for canonical Elm style
  • Fixes indentation, spacing, blank lines and layout automatically
  • Preserves Elm semantics – no refactors, only formatting
  • Deterministic output: same input ⇒ same formatted result
  • Optimized editor with Elm syntax highlighting and diff-friendly output
  • Paste code or upload a .elm file, then copy or download the result

🛠️ How to Use the Elm Formatter for elm-formatter

1

Paste or Upload Elm Code

Paste your Elm module into the editor or drop a .elm file from your project. The tool accepts any valid Elm 0.19 source.

2

Run the Formatter

Click the Format button. Your code is sent to a secure backend that runs elm-format and returns the canonical result.

3

Review the Output

Compare before/after in the editor. Imports, type aliases, cases and pipelines are all normalized according to Elm style.

4

Copy or Download

Copy the formatted code back into your editor or download the .elm file and commit it to your repository.

Technical Details

Formatting Engine

The tool delegates all formatting to elm-format 0.19 (the official Elm formatter), ensuring identical output to local CLI usage.

Supported Inputs

Supports `.elm` files and Elm 0.19 modules. MIME types: `text/x-elm`, `text/plain`.

Style Configuration

AspectConfigurationNotes
IndentationFixed (canonical)elm-format enforces a single standard style
Line breaksCanonical layoutelm-format decides where to wrap long expressions
SpacingAutomaticRemoves inconsistent spacing around operators and commas
CommentsPreservedComments stay in place with aligned surrounding code

Environment & Limits

Formatting is performed server-side via a Node.js wrapper around elm-format. Inputs are validated for size and type before processing to protect service reliability.

Using elm-format in Your Project

For day-to-day work, you’ll usually run elm-format locally. Here are some common commands:

All platforms (installed elm-format)

Format a single file

elm-format src/Main.elm --yes

Rewrites Main.elm in place with canonical formatting.

Format an entire src directory

elm-format src/ --yes

Recursively formats all .elm files under src/.

When This Elm Formatter Shines

Everyday Elm Development

  • Quickly clean up experimental code before committing
  • Ensure consistent style across multiple Elm projects
  • Normalize code before opening a pull request
-- Before
main =   Html.text "Hello!"

-- After
main =
    Html.text "Hello!"

Teaching & Learning Elm

  • Show students how idiomatic Elm code is structured
  • Convert messy examples into clear, canonical snippets for slides and articles
  • Reduce distractions from style so learners can focus on types and architecture

Team Collaboration

  • Agree on “no bikeshedding” by delegating style to elm-format
  • Keep diffs clean and review comments focused on behaviour, not spacing
  • Onboard new Elm developers with a single, official formatting standard

❓ Frequently Asked Questions

What is elm-format?

`elm-format` is the official code formatter for Elm. It enforces a single, community-approved style so that all Elm code looks consistent, regardless of who wrote it.

Can I customize indentation or style?

No. A core Elm philosophy is “one way to format code”. elm-format intentionally has no style knobs—everyone uses the same layout so you never argue about spacing in code reviews.

Does formatting change how my program behaves?

Formatting only changes whitespace, line breaks and layout. As long as your original Elm code compiled, the formatted version should behave the same. If elm-format refuses to run, it usually means the code has a syntax error.

Is my code processed locally or on a server?

For this tool, formatting is performed on a secure backend that runs elm-format 0.19. Code is processed transiently to produce the formatted output; you should still avoid pasting highly sensitive secrets into any online tool.

Which Elm versions are supported?

The formatter targets Elm 0.19.x syntax. Older Elm 0.18 code may need manual updates before formatting.

Pro Tips

Best Practice

Add elm-format to your pre-commit hooks so code is always formatted before it hits main.

Best Practice

If elm-format refuses to run, treat it as a hint that your code has a syntax error—fix that first, then format.

Best Practice

Use this online formatter to quickly beautify snippets before posting them in issues, blog posts or Q&A sites.

Additional Resources

Elm Guide
Documentation
elm-format GitHub Repository
Documentation
Elm Language Home
Documentation

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