What is a required HTML attribute?

Required attributes are those that must be present on a specific element for valid HTML. For example, alt on img, src on img and script, href on a and link, and action on form.

What happens if I use an invalid HTML attribute?

Browsers ignore attributes they do not recognise, so invalid attributes usually cause no visible error. However, they make your code harder to maintain, may cause unexpected behaviour in some parsers, and will be flagged by validators and linters.

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Validate HTML Attributes Online

HTML attributes must follow strict naming, syntax, and value rules. FixTools validates your attribute usage — checking for required attributes, invalid attribute names, malformed values, and deprecated attributes that could cause rendering issues.

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Validates attribute names and values

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Checks required attributes per element

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Flags deprecated attribute usage

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How to use this tool

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Paste HTML and validate. Attribute errors — missing required attributes, invalid values, and deprecated usage — are reported with specific guidance.

How It Works

Step-by-step guide to validate html attributes online:

1
Paste HTML to validate
Paste the HTML with attributes you want to check.
2
Validate
Click Validate to check all attribute names and values.
3
Fix attribute errors
Add missing required attributes, fix incorrect values, and replace deprecated attributes.
4
Re-validate
Confirm all attribute errors are resolved.

Real-world examples

Common situations where this approach makes a real difference:

Auditing data-* attribute naming conventions

In large projects, data-* attribute names can drift over time. Validating HTML ensures all custom attributes follow the correct data-* format and naming convention.

Checking ARIA attribute usage in an interactive component

Complex interactive components (tabs, accordions, modals) use many ARIA attributes. Validate the HTML to ensure aria-expanded, aria-controls, and aria-labelledby values are correctly set.

When to use this guide

Use this when auditing HTML for compliance, checking that data-* attributes follow naming conventions, or verifying ARIA attribute values are correct.

Pro tips

Get better results with these expert suggestions:

Images must have alt attributes

alt is a required attribute on every <img> element. Omitting it is an HTML error and an accessibility failure.

Use data-* for custom attributes

Custom attributes must use the data-* prefix. Attributes like <div myattr="value"> are invalid HTML and will be flagged during validation.

Boolean attributes do not need values

Boolean HTML attributes (required, disabled, checked) do not need an explicit value. <input required="required"> and <input required> are both valid, but <input required="true"> is incorrect.