Validate HTML Form Code

Auditing an existing contact form for accessibility

Run the form HTML through the validator to identify inputs without labels, missing required attributes, and any structural errors that could break form submission. The validator turns a vague accessibility concern into a concrete list of fixes, each tied to a specific element in the markup. Resolving the list closes the gap between an accessibility audit and the underlying code, and the same validator becomes a regression guard that catches new accessibility breaks introduced by future edits.

Testing a newly built form before integration

Validate form HTML before connecting it to a backend to ensure the structure is correct and all field associations are properly defined. Catching markup errors at this stage prevents the confusion of debugging a submission flow when the underlying form is structurally broken. Once the validator panel is clean, any later submission failure can be attributed to the integration layer rather than the markup, which dramatically narrows the search space for production bugs.

The most common form validation errors: missing <label> elements or for attributes that associate labels with inputs, missing name attributes on input elements (prevents form submission), missing required attribute on mandatory fields, and invalid input type values. Validate your form HTML to catch all of these before user testing.

Beyond HTML spec compliance, form elements need correct ARIA attributes for screen reader compatibility: aria-required for required fields, aria-describedby to associate error messages with inputs, aria-invalid on invalid fields, and aria-label for inputs without visible labels. The HTML validator catches spec errors; an accessibility checker catches ARIA gaps.

Every <input>, <select>, and <textarea> element should have a unique ID. Duplicate IDs are a validation error that breaks <label for='id'> associations: when two elements share an ID, the label only associates with the first one. Duplicate IDs are particularly common in dynamically generated form fields.

The <form> element requires a valid method (get or post) and a valid action URL. Missing action attributes default to the current page URL (which may be intentional). Invalid method values are a validation error. Ensure action URLs are properly encoded and do not contain unencoded special characters.

HTML forms require each input to have an associated label element (using for/id pairing or aria-label). Missing labels are accessibility errors that will be caught in validation.

Every <form> element should have explicit method (get or post) and action attributes. Forms without these rely on browser defaults which vary.

Always specify the type attribute on <input> elements (text, email, password, checkbox, etc.). The default type=text is browser-dependent and should not be assumed. Form validation is a particularly common source of HTML errors because forms have so many interacting elements: input types, validation attributes, label associations, fieldset groupings, button submit behaviour. A single missing for attribute on a label breaks accessibility for screen readers, while a missing name attribute on an input makes the field uncapturable in the submit payload. Our validator surfaces all these issues with specific location markers so you can fix the exact problematic element rather than scanning the whole form. Form validation also flags accessibility violations that pure markup checkers miss, like missing autocomplete attributes that hurt mobile usability or browser autofill performance. Forms also benefit from validation against browser auto-fill behaviour. Modern browsers heuristically detect form purpose (login, registration, shipping address) and auto-fill matching values, but they rely on specific autocomplete attribute values to do this reliably. A validator that flags missing or misspelled autocomplete attributes catches a usability issue that pure markup validators miss. Customers fill out forms faster, fewer abandon mid-form, and conversion rates improve measurably. For e-commerce, financial services, or any business where form-completion rates drive revenue, this attribute-level validation is a high-leverage improvement.