deno fmt

Deno ships with a built-in code formatter based on dprint that auto-formats your code to a consistent style. For a broader overview, see Linting and Formatting.

Basic usage

Format all supported files in the current directory:

deno fmt

Format specific files or directories:

deno fmt main.ts src/

Watch mode

Automatically re-format files when they change:

deno fmt --watch

Check formatting in CI

Use --check to verify files are formatted without modifying them. The command exits with a non-zero status code if any files are unformatted:

deno fmt --check

Add --fail-fast to stop on the first unformatted file instead of reporting all of them, which is useful in large codebases:

deno fmt --check --fail-fast

Formatting stdin

Format code piped through stdin — useful for editor integrations:

cat main.ts | deno fmt -

Configuring the formatter

Customize formatting options in your deno.json:

{
  "fmt": {
    "useTabs": false,
    "lineWidth": 80,
    "indentWidth": 2,
    "semiColons": true,
    "singleQuote": false,
    "proseWrap": "preserve"
  }
}

See the Configuration page for all available options.

Inheriting settings from .editorconfig

deno fmt also reads .editorconfig files and uses them to fill in any formatting option you have not set elsewhere. The precedence, from highest to lowest, is:

1. CLI flags (--indent-width, --use-tabs, and so on)
2. The fmt block in deno.json
3. .editorconfig
4. Built-in defaults

So .editorconfig only supplies values you have not already configured through a flag or deno.json. Properties such as indent_style, indent_size, and max_line_length map onto the corresponding deno fmt options.

Including and excluding files

Specify which files to format in deno.json:

{
  "fmt": {
    "include": ["src/"],
    "exclude": ["src/testdata/", "src/generated/**/*.ts"]
  }
}

You can also exclude files from the command line:

deno fmt --ignore=dist/,build/

Supported file types

The markup formatters (HTML, XML, SVG, and the --unstable-component formats) and the style formatters (CSS, SCSS, and Less) were rebuilt to only adjust whitespace. They never reorder or rewrite tokens, and they pass unknown syntax (vendor extensions, future at-rules, template expressions, even broken markup) through unchanged instead of erroring, so formatting is more robust on real-world files.

Ignoring code

JavaScript / TypeScript / JSONC

Ignore formatting code by preceding it with a // deno-fmt-ignore comment:

// deno-fmt-ignore
export const identity = [
    1, 0, 0,
    0, 1, 0,
    0, 0, 1,
];

Or ignore an entire file by adding a // deno-fmt-ignore-file comment at the top of the file.

Markdown / HTML / CSS

Ignore formatting next item by preceding it with <!--- deno-fmt-ignore --> comment:

<html>
  <body>
    <p>
      Hello there
      <!-- deno-fmt-ignore -->
    </p>
  </body>
</html>

To ignore a section of code, surround the code with <!-- deno-fmt-ignore-start --> and <!-- deno-fmt-ignore-end --> comments.

Or ignore an entire file by adding a <!-- deno-fmt-ignore-file --> comment at the top of the file.

YAML

Ignore formatting next item by preceding it with # deno-fmt-ignore comment:

# deno-fmt-ignore aaaaaa: bbbbbbb

deno fmt [OPTIONS] [files]...

deno fmt myfile1.ts myfile2.ts

JavaScript, TypeScript, Markdown, JSON(C) and Jupyter Notebooks

HTML, CSS, SCSS, LESS, YAML, Svelte, Vue, Astro and Angular

cat file.ts | deno fmt -

deno fmt --check

// deno-fmt-ignore

// deno-fmt-ignore-file