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Format HTML with Clean Attribute Structure

Long attribute lists are one of the most common sources of unreadable HTML.

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Preserves all attribute names and values exactly

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Correctly indents elements with long attribute lists

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Handles data-*, aria-*, and custom attributes

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<iframe
  src="https://www.fixtools.io/html/html-formatter?embed=1"
  width="100%"
  height="780"
  frameborder="0"
  style="border:0;border-radius:16px;max-width:900px;"
  title="HTML Formatter by FixTools"
  loading="lazy"
  allow="clipboard-write"
></iframe>

<iframe
  src="https://www.fixtools.io/html/html-formatter?embed=1"
  width="100%"
  height="780"
  frameborder="0"
  style="border:0;border-radius:16px;max-width:900px;"
  title="HTML Formatter by FixTools"
  loading="lazy"
  allow="clipboard-write"
></iframe>

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Attribute-Heavy HTML: The Formatting Challenge and the Solution

Modern HTML is far more attribute-heavy than the HTML of even a decade ago. A single form input might carry the type, id, name, placeholder, required, autocomplete, pattern, minlength, maxlength, and a handful of aria attributes describing its label, error message, and validation state. Add framework-specific bindings such as v-model, x-data, hx-get, or data-controller, and the attribute list can become longer than every other meaningful part of the element combined. In an unformatted file this entire list collapses into a single horizontally-scrolling line where verifying any individual attribute requires careful counting of quote marks. Attribute errors hide easily in this format, and many real-world accessibility bugs trace back to a single misspelled aria-labelledby reference or a missing required attribute that nobody noticed during review.

FixTools formats the HTML structure around attribute-heavy elements while leaving the attributes themselves untouched. The opening tag with all its attributes lives on the line for its element, indented to the correct nesting depth, with quoted values preserved as written, boolean attributes left in whatever form the source used, and custom data and aria attributes passed through without modification. The contextual indentation does most of the work even when the attribute list itself is long: knowing that the element sits two levels deep inside its parent gives the reader a clear position from which to scan the attributes. The combination of correct nesting and preserved attribute order produces output where attribute issues become noticeably easier to spot.

Some teams prefer attributes on separate lines, one per line, with the closing bracket on its own line as well. FixTools does not impose that layout, deliberately. Attributes-per-line formatting is opinionated and changes the diff shape significantly: a single attribute addition becomes a multi-line change, and the file length grows substantially. Teams that have decided to enforce this layout typically use Prettier with the htmlWhitespaceSensitivity option configured to do so. FixTools focuses on the structural indentation of the document and preserves whatever attribute layout the input already uses, which means if you have already adopted per-line attribute formatting in your source, the output will preserve it; if you haven't, the output will keep your attributes on a single line per element, indented to the right depth.

The strategic point about attribute formatting is that it interacts with code review more than almost any other aspect of HTML formatting. Attribute changes are common: a new aria attribute for an accessibility fix, a new data attribute for an analytics rollout, a new validation rule on a form field. Each of these is a small change to an attribute list, and the readability of that change in a diff depends entirely on the surrounding formatting. Files with clean structural indentation produce clean attribute diffs that reviewers can evaluate quickly. Files without that indentation produce diffs where reviewers have to first locate the changed line before they can even read it.

MDN: HTML attribute reference WAI-ARIA authoring practices

How to use this tool

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Paste your HTML with any number of attributes per element and click Format. Indentation is applied correctly and all attribute values are preserved without modification.

How It Works

Step-by-step guide to format html with clean attribute structure:

1
Paste your HTML
Paste HTML with any number of attributes per element into the input panel. The formatter handles elements with no attributes, single attributes, or dozens of attributes per element equally well.
2
Click Format
Click Format. Indentation is applied to the document structure while all attribute names and values are preserved exactly. Quoted values keep their quotes, boolean attributes stay as written, and custom attributes are passed through unchanged.
3
Review attribute visibility
Scan the formatted output to verify that all required attributes are present on each element, that aria references point to existing IDs, and that data attribute naming is consistent across elements.
4
Copy the formatted HTML
Copy the output for use in your editor, code review, or accessibility audit. The formatted result is plain text and pastes cleanly into any destination.

Real-world examples

Common situations where this approach makes a real difference:

Reviewing a form with complex ARIA attributes

A 25-element registration form uses aria-required, aria-invalid, aria-describedby, and several data attributes per input for client-side validation. After formatting the 18KB form HTML, the accessibility reviewer identifies two aria-describedby values pointing to element IDs that no longer exist in the form, plus an aria-labelledby reference that targets a hidden helper element that is actually the wrong one. All three issues were invisible in the original compressed source.

Auditing data attributes in a JavaScript-driven component

A tab component uses fourteen data-* attributes spread across its parent and child elements to control which tab is active, which is being hovered, which has a notification badge, and which has been visited before. Formatting the component's HTML reduces the audit time substantially by presenting each element's full attribute set in indented context rather than as a single compressed line that requires manual unspooling.

Verifying alt text coverage after an image audit

After formatting a 60KB marketing page, a developer scans the formatted output for img tags and finds eight images missing alt attributes in under five minutes. The same search in the unformatted file had previously been abandoned after thirty minutes because the developer kept losing their place in the wall of single-line markup. The formatting effort costs seconds and yields a complete audit in minutes.

Preparing an HTML form for third-party integration review

Before sending an HTML form to a third-party payment provider for security review, the team formats the form HTML. The reviewer confirms in their first pass that all required name attributes are present, no sensitive data attributes are exposed, and the autocomplete attributes are set to the values the payment provider expects. The review wraps up faster than expected because the formatted markup left nothing for the reviewer to puzzle over.

When to use this guide

Use this when your HTML has elements with many attributes that collapse into long unreadable lines, making it hard to verify that every attribute and value is correct.

Pro tips

Get better results with these expert suggestions:

Format HTML before an accessibility review

Accessibility reviewers spend most of their time on attribute-level details: alt text on every image, for-to-id associations between labels and form controls, role attributes on interactive elements, and aria-describedby references pointing to existing help text. Formatted HTML lays every attribute open in context, which can cut an accessibility audit time dramatically and increase the number of real issues caught. The investment of seconds spent formatting before the review pays back in hours saved during it.

Use formatted output to write CSS attribute selectors

When writing CSS or JavaScript that targets elements by attribute, for example a stylesheet rule matching [data-state="active"] or a Playwright selector matching [aria-expanded="true"], format the HTML first to see the exact attribute names and values in use. This prevents the common bug class where a selector silently fails because of a subtle attribute name difference, such as data-status versus data-state, that would have been visible immediately in formatted output.

Format before migrating to a new ARIA version

ARIA specifications evolve, and migrations from ARIA 1.1 to 1.2 or from 1.2 to 1.3 typically involve deprecating some attributes and changing the expected values of others. Formatting your HTML before an ARIA migration makes it straightforward to audit every existing aria-* attribute and identify which ones need to be updated, removed, or replaced. Without formatting, the same migration becomes a tedious search through compressed markup where many attributes are easy to miss.

Preserve attribute order manually for specification compliance

The HTML specification does not require any particular attribute order, but many teams adopt conventions, for example id first, then class, then name, then data attributes, then aria attributes. FixTools preserves whatever order your input already uses. If your team has decided on a specific order and existing files don't follow it, fix the order manually before pasting, and the formatter will preserve your corrected order in the output. The formatter never reorders attributes on its own, which is intentional: silent reordering would produce noisy diffs that obscured the real intent of changes.

Review aria attributes after formatting

Once your HTML is formatted, scan all aria-* attributes to verify that aria-labelledby, aria-describedby, and aria-controls values reference existing element IDs. Formatting makes these references visible in context.

Check data-* attribute consistency

After formatting, scan data-* attributes for consistent naming conventions. Formatting reveals when the same semantic data is stored under slightly different attribute names across elements.

Use formatting to verify required attributes

After formatting, scan input, img, and a elements to confirm they all have their required accessibility attributes: alt on img, href on a, and label associations on inputs.

FAQ

Frequently asked questions

No, attribute order is preserved exactly as supplied in the input. The formatter changes indentation and line breaks in the document structure but never modifies the ordering or content of attributes within a tag. This is a deliberate choice. Silent reordering would produce noisy diffs where every attribute change appeared to affect every other attribute on the same element, and the resulting reviews would be much harder. If your team has agreed on a specific attribute order, apply it manually before formatting and FixTools will preserve your intent.

No, attribute values are preserved exactly as written in the source. Quoted values keep their quote style, whether single or double. Boolean attributes are unchanged regardless of whether you wrote them as the bare attribute, the empty-string form, or the mirrored form with the attribute name as its own value. Custom data-* and aria-* attribute values pass through without any modification, which is essential because these values often encode JSON, HTML fragments, or other structured content that any change could corrupt.

FixTools preserves the attribute layout that the input already uses. If you want each attribute on its own line, arrange them that way before pasting, and the formatter will preserve that structure while correcting the overall indentation. For automatic conversion to per-attribute line formatting, Prettier with HTML support handles this, controlled by the singleAttributePerLine option. The reason FixTools doesn't enforce per-attribute formatting is that doing so is opinionated and would produce surprising large diffs for teams that have decided to keep attributes on a single line.

The Google HTML/CSS Style Guide and most popular team conventions recommend a specific order: class first or id first depending on the team's preference, then any attribute that affects the element's behavior such as type, name, src, or href, then state attributes such as disabled or required, then data-* attributes for application state, then aria-* attributes for accessibility, then any other attributes. The single most important property of attribute order is consistency across the codebase. Whatever order your team picks, applying it uniformly is more valuable than picking the theoretically optimal order.

Yes, boolean attributes are preserved exactly as written. Whether your source uses the bare attribute form such as disabled, the empty-string form such as disabled="", or the mirrored form such as disabled="disabled", the formatter keeps the form you used without conversion. All three forms are valid HTML5 and render identically in browsers, so the choice is a stylistic one for the team. If your team has standardized on one form, applying it consistently in your source ensures the formatter's output also uses that form throughout.

Formatting makes missing attributes far easier to spot by visual inspection because each element sits in clear context with its attribute list visible alongside it. After formatting, a single pass through the file lets you scan img tags for alt attributes, input tags for type and name attributes, and a tags for href attributes. For programmatic detection of missing required attributes, the HTML Validator is the right complement to formatting: format first to make the file readable, validate next to catch any issues the eye missed.

Yes, long class attribute values are preserved exactly as written. Tailwind projects routinely have class attributes containing twenty or more utility classes per element, and these long values are passed through without truncation, wrapping, or modification. The element tag is indented correctly in the document structure, and the long class attribute sits on its line as part of the element. For teams that want long class attributes wrapped onto multiple lines, a Prettier plugin specifically for Tailwind handles that case.

Yes, custom element attributes, framework-specific bindings such as Vue's v-bind and :class syntax, Angular's bracketed [attr] syntax, Alpine.js x-data and x-on directives, htmx attributes such as hx-get and hx-target, and any non-standard attribute name are preserved exactly as written. The formatter does not validate attribute names against any specification. Its job is whitespace and indentation, and it treats whatever appears between the angle brackets as opaque content that the surrounding structure organizes but does not interpret.

Attribute values containing escaped quotes, ampersands, or other HTML entities are preserved exactly as supplied. The formatter does not re-escape, unescape, or normalize entity references. If your attribute value contains an embedded quote escaped as ", that escape stays in the output. This matters for data attributes containing embedded JSON or HTML fragments, where any modification to the escape sequences would corrupt the data.

For attribute lists that encode non-obvious behavior, yes. An HTML comment above an element explaining what its data-* attributes do, or why a particular aria attribute is needed, costs almost nothing to add and helps every future reader understand the intent. The formatter preserves comments and places them on their own lines, so the comment sits as a clear marker above the element it describes. Reserve this for genuinely complex cases; over-commenting is its own problem and dilutes the value of the comments that actually matter.