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Check HTML for Accessibility Errors

HTML validation catches a meaningful subset of accessibility errors at the specification level: missing alt attributes on images, invalid ARIA role usage, missing labels on form inputs, and incorrect role-attribute combinations that the WAI-ARIA spec defines as errors.

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Flags missing alt attributes on images

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Validates ARIA role usage and attribute combinations

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Identifies inputs without label associations

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

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

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What HTML Validation Catches for Accessibility and What Requires Additional Tools

The HTML specification defines a set of accessibility requirements that are testable at the markup level, which means they can be checked statically by a validator without needing to render the page or simulate user interaction. Missing alt attributes on img elements are spec violations because alt is a required attribute on img in nearly all cases, with the only exception being purely decorative images where an empty alt attribute (alt="") is required to signal that the image carries no content meaning. Invalid ARIA role values are spec violations because the WAI-ARIA specification defines a finite list of valid ARIA role values, and using a role name that does not exist in that list (whether through typo or fabrication) is an error that the validator can identify by matching against the known role list. ARIA attribute usage on elements that prohibit those attributes, such as aria-checked on a div that does not have a role permitting that state, is also a spec violation that validators report.

However, HTML validation does not cover the full scope of accessibility requirements defined by WCAG, the Web Content Accessibility Guidelines that form the basis of most accessibility law and policy. WCAG 2.1 Level AA, which is the most commonly cited compliance target, has fifty success criteria covering a wide range of accessibility concerns, and many of these criteria require human judgment or runtime testing rather than static markup analysis. Validation cannot check whether alt text is meaningfully descriptive rather than just present, whether color contrast meets the minimum required ratios for normal and large text, whether interactive elements are reachable and operable via keyboard, or whether the reading order produced for screen reader users makes logical sense. These checks require dedicated accessibility testing tools such as axe, WAVE, or Lighthouse, plus manual testing with an actual screen reader operated by either an accessibility specialist or an end user.

The value of HTML validation as an accessibility step is that it eliminates the base layer of structural errors before deeper accessibility testing begins, which makes the deeper testing more productive and its results easier to interpret. An accessibility audit that finds twenty issues on a page with invalid underlying HTML is significantly harder to interpret than one performed on a page that starts from a clean HTML baseline, because errors in markup structure, ARIA roles, and label associations compound each other in ways that obscure the root causes. Validating HTML first produces a cleaner starting point for accessibility testing and reduces the risk of false positives in automated accessibility scanners that are caused by structural markup issues rather than genuine accessibility failures.

A practical accessibility workflow combines validation with several other checks in a defined sequence. Step one is HTML validation to catch spec-level errors. Step two is an automated WCAG checker like axe DevTools or Lighthouse to surface contrast issues, missing form labels in context, and other rule-based accessibility problems. Step three is manual keyboard navigation testing to confirm that all interactive elements are reachable and operable without a mouse. Step four is screen reader testing with VoiceOver, NVDA, or another assistive technology to verify that the page is usable by people who depend on these tools daily. No single tool catches everything, and the combination of all four steps provides much better coverage than any one of them alone.

HTML Living Standard (WHATWG)WAI-ARIA Specification (W3C)

How to use this tool

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Paste your HTML and validate. Pay close attention to errors about missing alt attributes, invalid ARIA roles, and inputs without associated labels. Fix all spec-level accessibility errors before running a full WCAG audit.

How It Works

Step-by-step guide to check html for accessibility errors:

1
Paste your HTML
Paste the full HTML source including all images, form elements, ARIA attributes, and interactive components. The validator needs the complete document context to apply accessibility-related rules correctly, particularly for ARIA attribute checking which depends on the surrounding role context.
2
Validate
Click the validate button to run the full spec-level accessibility check across all the rules the validator implements. The validator will scan every element and attribute and report any violations of the accessibility-relevant subset of HTML and ARIA spec rules.
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Fix ARIA and alt text errors
Address missing alt attributes on images, invalid ARIA role names that do not appear in the WAI-ARIA spec, ARIA attributes used on elements that do not support them, and form inputs that are missing proper label associations. These are the most common accessibility-related errors that validation surfaces.
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Revalidate
Confirm that all spec-level accessibility errors have been resolved by running another validation pass after your fixes. A clean validation result means you have a clean structural baseline ready for deeper accessibility testing with dedicated tools.
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Run a full accessibility audit
With a clean HTML baseline in place, run an automated WCAG checker such as axe DevTools, WAVE, or Lighthouse to find accessibility issues that go beyond what HTML validation can detect, and then test the page manually with a screen reader to verify the experience for assistive technology users.

Real-world examples

Common situations where this approach makes a real difference:

Pre-audit accessibility preparation

Before submitting a site to a formal accessibility audit by an external consultant or compliance team, a developer validates all HTML to eliminate spec-level errors that would have been caught for free. This reduces the audit findings to genuine WCAG issues rather than structural HTML problems that should never have been part of the audit scope in the first place, making the audit significantly more efficient and its results more actionable for the development team to address.

Reviewing ARIA usage in a component library

A shared component library uses ARIA roles and attributes extensively for custom interactive widgets like dialogs, tabs, and combobox controls. Validating the HTML output of each component catches three invalid ARIA role names that were typos in the source code, two aria-* attributes used on elements that do not support them according to the WAI-ARIA spec, and a button element with a conflicting role attribute that was added redundantly during a refactor and never cleaned up.

Checking image alt text in a CMS-generated page

A content management system allows editors to insert images into articles without enforcing the requirement that alt text be provided, relying on editor discipline rather than tooling to ensure accessibility. Validating a page after editorial updates catches images added without any alt attribute at all, as well as images with empty alt attributes that should have had descriptive text because the images convey information rather than being purely decorative.

Accessibility QA for a redesigned form

A redesigned contact form is validated as part of the QA process before user testing begins. Validation reveals that three input elements lost their label associations during the redesign because the for and id attributes on the label and input elements were not updated to match the new structure, and that an ARIA live region uses an invalid aria-live attribute value that does not match any of the values defined in the WAI-ARIA spec. Both issues are fixed before users see the form.

Pro tips

Get better results with these expert suggestions:

Empty alt and missing alt are different errors

A missing alt attribute on an img element is always a spec error that validators flag because alt is a required attribute. An empty alt attribute (alt="") is the correct markup for decorative images that carry no content meaning, because screen readers skip elements with alt="" rather than announcing them. Using alt="" on images that actually convey information is an accessibility error that the HTML validator cannot detect because it only checks for presence of the attribute, not the appropriateness of its content. That deeper check requires human judgment or a dedicated audit tool.

ARIA roles override native HTML semantics

Adding role="button" to a div changes how assistive technologies treat the element, overriding the div's lack of inherent semantics with the explicit button role. However, ARIA roles do not add interactive behavior to the element: a div with role="button" must also handle keyboard events for Enter and Space key presses to be operable by keyboard users, and must manage focus correctly. The validator catches invalid role names but cannot check whether the required interactive behavior has been implemented in JavaScript, which is one of the most common accessibility failures in custom components.

aria-label and aria-labelledby can conflict

If both aria-label and aria-labelledby are present on the same element, the aria-labelledby attribute takes precedence according to the WAI-ARIA accessible name calculation algorithm. Having both attributes present is not a hard spec violation but is redundant and potentially confusing for anyone maintaining the code later. Validators may emit a warning about this combination. Use one approach consistently across your components rather than mixing both on the same element, and document the chosen convention in your component library style guide.

Validate before accessibility testing, not instead of it

HTML validation catches spec-defined accessibility errors only, which is a small subset of the full WCAG rule set. WCAG compliance requires testing color contrast ratios across all text and UI components, keyboard operability of every interactive element, reading order through the page, form error messaging patterns, focus management during dynamic content updates, and much more that no static validator can check. Treat spec validation as step one of a complete accessibility testing workflow, not as a substitute for the other steps in that workflow.

FAQ

Frequently asked questions

HTML validation checks the spec-defined requirements of the HTML and WAI-ARIA specifications, which include some accessibility-relevant rules such as missing alt attributes on images, invalid ARIA role names, and unassociated form labels. However, full WCAG compliance testing requires additional tools beyond HTML validation. WCAG 2.1 Level AA has fifty success criteria, and many require runtime testing, contrast measurement against the page background, keyboard operability testing with real interaction, and human judgment about whether content meets the criteria. Static markup validation cannot provide all of these checks.

HTML validation catches invalid ARIA role names (role values not defined in the WAI-ARIA specification), ARIA attributes used on elements that do not support them according to the role-attribute compatibility matrix, abstract ARIA roles used directly in markup (abstract roles are specification-only and must not be used in HTML), and required ARIA attributes missing from elements that need them based on their assigned role. It does not catch ARIA usage that is technically valid but semantically incorrect, such as a role that is allowed on an element but does not match the actual purpose of that element in the page.

No, alt="" is valid only for decorative images that do not convey any content meaning to the reader. The HTML spec requires a non-empty alt value for images that convey information, communicate meaning, or function as part of the content rather than as visual decoration. An image of a company logo, a product photograph, an infographic, or any image with text on it requires descriptive alt text. Only images that are truly decorative, such as a background texture, a decorative divider, or a spacer image used for layout, should have alt="" to signal to screen readers that the image can be skipped.

HTML validation checks that the markup conforms to the HTML specification, focusing on syntactic and structural correctness with some accessibility-relevant checks included. An accessibility audit checks that a page is usable by people with disabilities, typically against the WCAG guidelines or another accessibility standard. Validation catches spec-defined errors including some accessibility requirements. An accessibility audit additionally covers contrast ratios, keyboard navigability, screen reader compatibility, cognitive accessibility considerations, and many other factors that require runtime testing and human judgment beyond what any static validator can provide.

After achieving zero HTML validation errors, the next steps are axe DevTools (a browser extension by Deque that performs automated WCAG checking with high accuracy), WAVE (a free tool from WebAIM that provides visual accessibility feedback overlaid on the page), and Lighthouse in Chrome DevTools (a built-in audit tool that combines accessibility, performance, and SEO checking). After automated tools have been used, test manually with a screen reader: VoiceOver on macOS, NVDA on Windows, or TalkBack on Android represent the most common assistive technology combinations used by real users of your site.

No, a valid ARIA role only means that the role name exists in the WAI-ARIA specification and is being used in a syntactically correct way. It does not guarantee that the element actually provides the expected behavior to assistive technology users. An element with role="button" must respond to keyboard events for Enter and Space, manage focus correctly when activated, and provide a visible focus indicator that meets contrast requirements. These behaviors must be implemented with JavaScript and CSS that the validator cannot inspect. ARIA roles express intent to assistive technologies but do not automatically implement the required interactive behavior.

After pasting the HTML into FixTools and running validation, look for errors with the word "alt" in the description text. Each missing alt attribute error includes a location with a line number and the relevant element. For large pages, you can also search the raw HTML for img elements and verify that each one has an alt attribute, which is a useful sanity check against the validator output. The validator reports every instance of a missing alt attribute, so a single validation pass finds every missing alt in the pasted HTML without requiring repeated checks.

A link element without any text content needs an accessible name from somewhere, and aria-label provides that name when the visible text is not sufficient. However, validators may flag certain patterns of aria-label usage on links as warnings, particularly when the linked content is an image that already has alt text, when the aria-label duplicates information visible elsewhere, or when the link wraps content that would naturally provide an accessible name. Review each flagged instance to confirm whether aria-label is genuinely needed or whether the link could be made accessible through its content alone.

Yes, every form input that accepts user data should have an associated label that describes what the input is for. The most common pattern is a label element with a for attribute matching the input id, which creates an explicit programmatic association that screen readers expose to users. Other patterns include wrapping the input inside the label element for an implicit association, or using aria-label or aria-labelledby when a visible label is not appropriate for the design. HTML validation catches inputs that have no label at all, but cannot verify whether the labels that are present are meaningfully descriptive.

The immediate effect varies depending on the error and the user. Missing alt text on a meaningful image leaves screen reader users without the information that image conveys, potentially making the page partially or fully unusable for them. Invalid ARIA roles confuse assistive technologies and may produce incorrect announcements or navigation behavior. Unlabeled form inputs make the form unusable for screen reader users because they cannot tell what each input is for. Beyond the impact on users, sites with significant accessibility errors may face legal exposure under accessibility legislation that applies in your jurisdiction.