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Linter Rule: No underscores on attribute names

Rule: html-no-underscores-in-attribute-names

Description

Warn when an HTML attribute name contains an underscore (_). According to the HTML specification, attribute names should use only lowercase letters, digits, hyphens (-), and colons (:) in specific namespaces (e.g., xlink:href in SVG). Underscores are not valid in standard HTML attribute names and may lead to unpredictable behavior or be ignored by browsers entirely.

Rationale

Underscores in attribute names violate the HTML specification and are not supported in standard markup. Their use is almost always accidental (e.g., mistyping data-attr_name instead of data-attr-name) or stems from inconsistent naming conventions across backend or templating layers.

Examples

✅ Good

<div data-user-id="123"></div>

<img aria-label="Close" alt="Close">

<div data-<%= key %>-attribute="value"></div>

🚫 Bad

<div data_user_id="123"></div>

<img aria_label="Close" alt="Close">

<div data-<%= key %>_attribute="value"></div>

References

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