Bad value “” for attribute “maxlength” on element “input”: The empty string is not a valid non-negative integer.

The HTML specification defines maxlength as accepting only a valid non-negative integer — a string of one or more ASCII digits representing a number greater than or equal to zero. An empty string does not satisfy this requirement, so the W3C validator flags it as an error. This commonly happens when a value is dynamically generated by a CMS, template engine, or JavaScript framework and the value ends up blank, or when a developer adds the attribute as a placeholder intending to fill it in later.

Why this matters

While most browsers silently ignore an empty maxlength and impose no character limit, relying on this behavior is problematic for several reasons:

• Standards compliance: Invalid HTML can lead to unpredictable behavior across different browsers and versions. What works today may not work tomorrow.
• Accessibility: Assistive technologies may read or interpret the maxlength attribute to communicate input constraints to users. An empty value could cause confusing or incorrect announcements.
• Maintainability: An empty maxlength is ambiguous — it’s unclear whether the developer intended no limit, forgot to set a value, or a bug caused the value to be missing.

How to fix it

You have two options:

1. Set a valid non-negative integer: Provide a concrete number that represents the maximum number of characters the user can enter, such as maxlength="100".
2. Remove the attribute: If you don’t need to enforce a character limit, simply omit maxlength altogether. There is no need to include it with an empty value.

Valid values for maxlength include "0", "1", "255", or any other non-negative whole number. The following are not valid: empty strings (""), negative numbers ("-1"), decimal numbers ("10.5"), or non-numeric strings ("none").

Where maxlength applies

The maxlength attribute is meaningful on text-entry input types: text, search, url, tel, email, password, and also on the textarea element. For non-text input types like number, date, range, or checkbox, the attribute has no effect and should not be used.

Examples

❌ Incorrect: empty string triggers the validation error

<input type="text" name="username" maxlength="">

❌ Incorrect: other invalid values

<input type="text" name="username" maxlength="-1">
<input type="email" name="email" maxlength="none">
<input type="text" name="bio" maxlength="10.5">

✅ Correct: explicit maximum length

<input type="text" name="username" maxlength="30">

✅ Correct: omit the attribute when no limit is needed

<input type="text" name="comment">

✅ Correct: maxlength on a textarea

<textarea name="bio" maxlength="500"></textarea>

✅ Correct: dynamic value with a fallback

If your maxlength value comes from a template or CMS, make sure you either output a valid number or omit the attribute entirely. For example, in a templating language, use conditional logic:

<!-- Only render maxlength if the value is set -->

<input type="text" name="username" maxlength="100">

Rather than rendering an empty attribute like maxlength="", ensure your template skips the attribute when no value is configured.

Learn more:

MDN Reference

<input>: The Input (Form Input) element - MDN

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MDN Reference

maxlength - MDN

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