For one formatter across HTML, CSS, and JavaScript, use Prettier. It parses and reprints code in a consistent style, rather than preserving your existing line breaks and indentation. If you want separate commands and more direct control over indentation and wrapping, use js-beautify instead. In either case, inspect the resulting diff: formatting is not a substitute for checking that the page still renders as intended.
Choose a formatter for the result you want
Prettier is the straightforward choice when your goal is to make HTML, CSS, and JavaScript in a project follow one consistent style. Its official documentation lists JavaScript, CSS, Less, SCSS, and HTML among its supported languages. Prettier is opinionated: it parses the input and prints it again according to its formatting rules, removing the original styling rather than trying to preserve the author’s layout (Prettier documentation).
Choose js-beautify if you prefer dedicated commands for JavaScript, CSS, and HTML, or want to adjust indentation and wrapping. Its package documentation also describes handling JavaScript and CSS inside HTML (js-beautify package documentation).
| Need | Better starting point | Trade-off |
|---|---|---|
| A consistent style across several supported languages | Prettier | It is opinionated and reprints the code, so the result may differ substantially from the original layout. |
| Separate HTML, CSS, and JavaScript commands | js-beautify | Its package describes controls for indentation and wrapping; you need to choose and maintain the style settings you want. |
| Format in a browser without Node.js | Prettier standalone | The browser build needs a parser and plugins and does not provide project configuration files, ignore files, CLI use, or automatic plugin loading. |
There is no single best choice for every project. The useful distinction is whether you value a consistent, opinionated result or more direct control over the formatting knobs.
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Format files in a project with Prettier
In a typical project workflow, install Prettier in the project and run it against the files you want to format. Run the commands from the project directory. Replace the example paths with actual files in your project.
- Install it as a project dependency. For an npm-based project, run:
npm install --save-dev prettier - Format the files. Specify the HTML, CSS, and JavaScript files explicitly so you can see what is included:
npx prettier --write index.html styles.css app.js - Review the changes. Inspect your version-control diff before treating the formatted output as the project’s new style baseline. Pay particular attention to HTML containing inline elements, text nodes, or templates.
- Make the workflow repeatable. Add the formatter configuration and ignore rules your project needs, then use the same settings for future formatting runs. The Prettier browser build does not read those project files; use the normal project workflow when they matter.
The command asks Prettier to write the formatted output to the named files. If you want to see what formatting would change before writing, omit --write and run the command without it; check the output before applying the result. Prettier normally selects the parser from each file’s extension. If you need to format a fragment or a file without a recognizable extension, consult the official documentation for the applicable parser option.
Format HTML, CSS, and JavaScript deliberately
HTML: check whitespace-sensitive content
HTML whitespace is the main reason not to treat a formatter run as a purely cosmetic operation. Whitespace between text and inline elements can affect what a browser displays. Prettier provides an htmlWhitespaceSensitivity option with three modes: css, strict, and ignore. Choose deliberately for the project rather than changing the setting just to make one diff look smaller. After formatting, inspect both the diff and the rendered page wherever text-node spacing, inline content, templates, or email HTML could be affected (Prettier options).
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CSS: preserve the project’s rules, improve its layout
Prettifying CSS changes its presentation as source code; it does not decide whether a selector or declaration is correct. Use the CSS parser for CSS files, and include Less or SCSS files only when your chosen formatter workflow supports them. Prettier lists CSS, Less, and SCSS as supported languages. If your project relies on a particular style, keep its formatter settings with the project instead of relying on each developer’s local preferences.
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JavaScript: formatting is not code repair
Formatting JavaScript makes its structure easier to scan, but it does not guarantee that the program runs correctly or change the intended behavior of the code. Review the diff for surprising edits, then use the project’s usual checks to catch errors beyond formatting. Prettier’s documented support for JavaScript makes it a natural fit when the same project also contains HTML and CSS (Prettier documentation).
Files with embedded code
When a file mixes HTML with embedded JavaScript or CSS, do not assume that formatting the surrounding file will produce the exact embedded-code behavior or layout you want. Prettier’s browser build requires a parser and plugins, and it does not load plugins automatically. For project work, use the normal Prettier setup and check the documentation for the language and embedded syntax in question. js-beautify’s package description specifically mentions JavaScript and CSS inside HTML and offers indentation and wrapping controls, which may suit workflows centered on that kind of file (js-beautify package documentation).
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Use js-beautify when you want dedicated commands
js-beautify provides separate commands named html-beautify, css-beautify, and js-beautify. That can make it easy to target one language at a time. Its package documentation describes controls for indentation and wrapping, so it is worth considering when those manual controls matter more than getting a single opinionated style across the project (js-beautify package documentation).
Use the package’s documentation to select the installation method and options that match your environment. Avoid copying a command from an unrelated version or environment: the available package commands and their options are documented by the package, and can change between releases. As with Prettier, run it on a small, representative set first, inspect the output, and only then apply your selected settings to more files.
Format in a browser without installing Node.js
Prettier’s standalone browser build is an option when you need formatting in a browser-based workflow. The Prettier browser documentation says this version does not depend on Node.js. It also explains the important limits: the standalone build needs a parser and plugins, and it does not support configuration files, ignore files, CLI usage, or automatic plugin loading (Prettier browser documentation).
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This makes standalone useful for a controlled browser integration, not a drop-in replacement for project formatting. If the desired result depends on a project configuration or ignore file, use Prettier in the project instead. If you choose standalone, provide the parser and plugins your inputs need and verify the result against the same examples you use in development.
Review formatting changes before adopting them
- Check scope: confirm the formatter touched only the files you intended to include.
- Inspect the diff: look for unexpected changes, especially in generated files, templates, or files that combine markup and code.
- Check HTML in a browser: compare rendered output when spacing between text or inline elements could matter. Give email HTML particular attention.
- Keep style decisions consistent: put the project’s chosen configuration and ignore rules in the normal project workflow so later runs do not depend on one person’s local setup.
- Separate formatting from functional validation: run the project’s existing checks after reviewing the formatting diff. A formatter makes code more consistently laid out; it is not a rendering test or a correctness guarantee.
Troubleshooting common formatting problems
The browser build cannot find a parser or plugin
The standalone build does not automatically load plugins. Supply the parser and plugins needed for the input, or use a normal project installation where your project workflow can manage them. For browser-specific limitations, see the Prettier browser documentation.
The browser formatter ignores project settings
That is a limitation of standalone use: it does not support configuration or ignore files. Switch to a project-based Prettier workflow when those files are part of the expected result.
The diff is much larger than expected
Prettier removes the original styling and prints parsed code in its own consistent style, so large changes to indentation and line breaks are expected. Confirm that you targeted the right files and review the diff before accepting it as a baseline. If you specifically want to tune indentation or wrapping, try js-beautify and its documented controls.
HTML looks different after formatting
Inspect whitespace around text nodes and inline elements. Review Prettier’s htmlWhitespaceSensitivity modes—css, strict, and ignore—and compare the rendered page after choosing a setting. Do not rely on the source diff alone for templates or email HTML (Prettier options).
Code inside HTML does not format as expected
Check whether your tool and setup support the embedded language in that file. Prettier standalone requires the appropriate parser and plugins; js-beautify documents JavaScript and CSS inside HTML. If a file mixes languages, test the exact file type and syntax rather than assuming the settings for a standalone .js or .css file will produce the same result.
Or skip the browser setup
After formatting HTML, a screenshot can help you check the rendered page; it does not prettify the source code. ScreenshotNeo is a website screenshot API and MCP server. One GET request can return an image or PDF, and its response identifies whether a page was clean, blocked, blank, timed out, failed to load, or served from cache. Cookie banners are accepted and removed before capture along with known consent platforms, newsletter popups, and chat widgets; each of those steps can be turned off. Bot checks, blank pages, timeouts, failed loads, and cache hits are not billed. AI agents can use its MCP server tools, including take_screenshot, get_page_info, and capture_pdf. Plans include 1,000 screenshots per month free with no card, with paid plans starting at $5 for 3,000 shots. See ScreenshotNeo and its API documentation.
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FAQ
Can formatting fix broken HTML, CSS, or JavaScript?
No. A formatter changes source layout; it is not a general-purpose repair or validation tool.
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