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

The maxlength attribute provides built-in client-side validation that caps the number of characters a user can type into a field. Browsers enforce this by preventing further input once the limit is reached. However, this behavior only makes sense for input types that accept arbitrary text strings. Input types like number, date, range, and checkbox have their own value formats and constraints — a number input’s value is controlled by min, max, and step, not by character count.

When you place maxlength on an unsupported input type, browsers will ignore the attribute. This means it provides no actual validation while giving a false sense of security. It also produces invalid HTML, which can cause issues with assistive technologies that may try to interpret the attribute and relay incorrect information to users. Keeping your markup valid ensures predictable behavior across browsers and a better experience for all users.

How to fix it

1. Remove maxlength from any <input> whose type is not email, password, search, tel, text, or url.
2. Use the correct constraint attributes for the input type in question. For number inputs, use min and max. For date inputs, use min and max with date strings.
3. If you genuinely need character-length validation, consider whether a text-based input type is more appropriate for your use case, or implement the constraint in JavaScript.

Examples

❌ Invalid: maxlength on a number input

<label for="quantity">Quantity</label>
<input type="number" id="quantity" name="quantity" maxlength="3">

The number type does not support maxlength. Browsers will ignore it, and the HTML is invalid.

✅ Fixed: using min and max for a number input

<label for="quantity">Quantity</label>
<input type="number" id="quantity" name="quantity" min="0" max="999">

If the goal was to limit the value to three digits, min and max are the correct constraints.

❌ Invalid: maxlength on a date input

<label for="start-date">Start date</label>
<input type="date" id="start-date" name="start-date" maxlength="10">

Date inputs have a browser-provided date picker, and their values are always in YYYY-MM-DD format. The maxlength attribute has no effect here.

✅ Fixed: using min and max for a date input

<label for="start-date">Start date</label>
<input type="date" id="start-date" name="start-date" min="2020-01-01" max="2030-12-31">

❌ Invalid: maxlength on a checkbox

<label>
  <input type="checkbox" name="agree" maxlength="1"> I agree
</label>

A checkbox is a boolean toggle — character length is meaningless here.

✅ Fixed: removing the invalid attribute

<label>
  <input type="checkbox" name="agree"> I agree
</label>

✅ Valid: maxlength on supported text-based types

<label for="username">Username</label>
<input type="text" id="username" name="username" maxlength="30">

<label for="user-email">Email</label>
<input type="email" id="user-email" name="email" maxlength="254">

<label for="user-phone">Phone</label>
<input type="tel" id="user-phone" name="phone" maxlength="15">

<label for="site-url">Website</label>
<input type="url" id="site-url" name="website" maxlength="2048">

<label for="user-pass">Password</label>
<input type="password" id="user-pass" name="password" maxlength="128">

<label for="query">Search</label>
<input type="search" id="query" name="q" maxlength="100">

All six of these input types support maxlength because they accept free-form text where limiting character count is meaningful.

Learn more:

MDN Reference

HTML input element - Attributes

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MDN Reference

HTML attribute: maxlength

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WHATWG Spec

WHATWG HTML Standard - Forms

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