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name: unique-id description: "Use when reviewing templates, rendered HTML, or shared components related to Ensure all IDs are unique. Validate the final browser-facing markup, not just the source framework abstraction." metadata: category: html priority: high difficulty: beginner estimatedTime: "10" source: frontendchecklist.io url: https://frontendchecklist.io/rules/html/unique-id

Ensure all IDs are unique

Duplicate IDs break form accessibility (labels don't connect), ARIA relationships fail, and JavaScript getElementById returns wrong elements—causing silent bugs.

Quick Reference

• Each ID must appear only once per HTML document
• Use classes for styling, IDs for unique anchors/references
• Check for duplicates introduced by component libraries
• Duplicate IDs break form labels, ARIA, and getElementById

Check

Scan this HTML document to ensure all ID attributes are unique across the entire page and properly reference related elements.

Fix

Remove duplicate ID values, ensure each ID is used only once per page, and update any references like labels, ARIA attributes, or JavaScript selectors.

Explain

Explain why unique IDs are essential for HTML validity, accessibility (form labels, ARIA), JavaScript functionality, and CSS styling.

Code Review

Review templates, server-rendered HTML, and shared components that output markup related to Ensure all IDs are unique. Flag exact elements, attributes, and routes where the rendered HTML violates the rule.

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For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/rules/html/unique-id