HTML Guide

Bad value X for attribute “checked” on element “input”.

checked is a boolean attribute and should not have a value; it must be written as just checked.

The checked attribute is used with <input> elements of type checkbox or radio. As a boolean attribute, it is either present (interpreted as true) or omitted (false). Adding any value, like checked="true", is not valid and causes a validation error. The correct usage is simply checked.

Incorrect example:

<input type="checkbox" checked="true">

Correct example:

<input type="checkbox" checked>

Example in context:

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Checkbox Example</title>
</head>
<body>
  <label>
    <input type="checkbox" checked>
    Subscribe to newsletter
  </label>
</body>
</html>

Learn more:

Related W3C validator issues

Bad value “true” for attribute “disabled” on element “input”.

Use the boolean attribute disabled without any value or with the attribute name as the value; "true" is invalid.

Detailed explanation

The HTML boolean attribute disabled indicates that the element is not editable, focusable, or submittable. For boolean attributes (per the WHATWG HTML standard and MDN), the presence of the attribute means “on/true,” and its absence means “off/false.” Valid syntaxes are:

disabled
disabled=""
disabled="disabled"

Invalid values include arbitrary strings like "true" or "false". Using disabled="true" triggers the validator error because boolean attributes must not use non-empty values other than the attribute name itself.

Relevant elements that support disabled include input, button, select, textarea, optgroup, option, fieldset, and form (partial behavior). For dynamic enabling/disabling, set or remove the attribute via JavaScript rather than assigning string values.

HTML examples

Reproduce the validator error (invalid)

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Invalid Disabled Example</title>
</head>
<body>
  <form>
    <input type="text" disabled="true">
    <button type="submit" disabled="false">Submit</button>
  </form>
</body>
</html>

Fix (valid boolean attribute usage)

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Valid Disabled Example</title>
</head>
<body>
  <form>
<!-- Presence means disabled -->

    <input type="text" disabled>
<!-- Also valid: disabled="disabled" or disabled="" -->

    <button type="submit" disabled="disabled">Submit</button>
  </form>
</body>
</html>

An “input” element with a “type” attribute whose value is “hidden” must not have an “autocomplete” attribute whose value is “on” or “off”.

The autocomplete attribute is used to control if the browser can provide assistance in filling out form field values, and it only makes sense for visible, not hidden, inputs.

It is available on <input> elements that take a text or numeric value as input, <textarea> elements, <select> elements, and <form> elements.

To fix this issue, you can remove the autocomplete attribute from the input element with type=hidden. Here is an example:

<!-- Wrong code -->

<input type="hidden" name="phone" value="12345" autcomplete="off">

<!-- Correct code -->

<input type="hidden" name="phone" value="12345">

An “input” element with a “type” attribute whose value is “hidden” must not have any “aria-*” attributes.

The aria-* attributes are part of the WAI-ARIA (Web Accessibility Initiative-Accessible Rich Internet Applications) suite. They are used to improve the accessibility of web pages. However, when we use an input element with a type attribute whose value is hidden, we imply that the element is invisible and has no interaction with the user. Therefore, it doesn’t make sense to add aria-* attributes to it.

To fix this issue, you need to remove the aria-* attributes from the input element with type=hidden. Here is an example:

<!-- Wrong code -->

<input type="hidden" name="referer" value="https://example.com" aria-invalid="false">

<!-- Correct code -->

<input type="hidden" name="referer" value="https://example.com">

Any “input” descendant of a “label” element with a “for” attribute must have an ID value that matches that “for” attribute.

When nesting an input element inside a label that has a for attribute, the id attribute of the input is required to match it.

The label element represents a caption in a user interface. The caption can be associated with a specific form control, known as the label element’s labeled control, either using the for attribute, or by putting the form control inside the label element itself.

When the input is inside the label, there’s no need to specify a for attribute as there can only be one input, as in this example:

<label>
  Age
  <input type="text" name="age">
</label>

However, if the for attribute is specified, then it must match the id of the input like this:

<label for="user_age">
  Age
  <input type="text" name="age" id="user_age">
</label>

Attribute “maxlength” is only allowed when the input type is “email”, “password”, “search”, “tel”, “text”, or “url”.

Attribute “minlength” is only allowed when the input type is “email”, “password”, “search”, “tel”, “text”, or “url”.

The minlength attribute can be used on an input element to define a client-side validation for the maximum length allowed on an input without resorting to JavaScript.

This attribute is only allowed on elements of type email, password, search, tel, text, or url.

The minlength attribute defines the minimum number of characters (as UTF-16 code units) the user can enter into an <input> or <textarea>. This must be an integer value 0 or higher. If no minlength is specified, or an invalid value is specified, the input has no minimum length. This value must be less than or equal to the value of maxlength, otherwise the value will never be valid, as it is impossible to meet both criteria.

Here’s an example:

<label for="name">Enter your name (max 25 characters)</label>
<input type="text" minlength="25" id="name">

Attribute “pattern” is only allowed when the input type is “email”, “password”, “search”, “tel”, “text”, or “url”.

Bad value “0” for attribute “step” on element “input”: Zero is not a valid positive floating point number.

The step attribute is a number that specifies the granularity that the value must adhere to.

It sets the stepping interval when clicking up and down spinner buttons, moving a slider left and right on a range, and validating the different date types.

When used, it must be greater than zero.

Example:

<form>
<!-- Valid values include 1.3, 3.3, 5.3, 7.3, 9.3, 11.3, and so on -->

  <input id="myNumber" name="myNumber" type="number" step="2" min="1.3" />
</form>

Bad value “combobox” for attribute “role” on element “input”.

The role attribute value combobox is not valid on an input element according to the W3C HTML standard.

The role="combobox" is valid only when applied to an element that acts as a container for the combo box widget, usually a div or similar element, and not directly to a native HTML input. Native input elements of type "text" or "search" already have implicit roles and accessibility semantics. To create an accessible combobox, wrap the input inside a container element with role="combobox" and use appropriate ARIA attributes.

Incorrect Implementation:

<input type="text" role="combobox" aria-autocomplete="list">

Correct Implementation:

<div role="combobox" aria-haspopup="listbox" aria-owns="suggestions" aria-expanded="false">
  <input type="text" aria-autocomplete="list" aria-controls="suggestions">
</div>
<ul id="suggestions" role="listbox">
  <li role="option" id="option1">Option 1</li>
  <li role="option" id="option2">Option 2</li>
</ul>

Explanation of attributes:

role="combobox": Applied to the container (<div>) to define the accessible widget.
aria-haspopup="listbox": Indicates the presence of a list of suggestions.
aria-owns / aria-controls: Connects the input and suggestion list.
aria-expanded: Denotes whether the suggestion list is visible.
aria-autocomplete: Defines the autocomplete behavior.

This markup ensures better accessibility and passes W3C validation.

Bad value “datetime” for attribute “type” on element “input”.

type="datetime" is obsolete; it was removed from HTML and is not valid in modern browsers or validators.

Explanation

The input element’s type attribute accepts specific keywords defined by the HTML Living Standard. The keyword datetime was dropped; use either:

type="datetime-local" for a local date and time without timezone.
type="date" or type="time" when collecting them separately.
type="text" with a pattern or a JS widget when timezone-aware datetime is required.

Relevant attributes that still apply include name, value, min, max, and step (e.g., seconds for datetime-local).

HTML examples

Example reproducing the error

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Invalid input type</title>
</head>
<body>
  <form>
    <label>
      Meeting:
      <input type="datetime" name="meeting">
    </label>
  </form>
</body>
</html>

Valid fix with datetime-local

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Valid input type</title>
</head>
<body>
  <form>
    <label>
      Meeting:
      <input type="datetime-local" name="meeting" step="60">
    </label>
  </form>
</body>
</html>