noDuplicateProperties

CSS

Summary

• Rule available since: v1.9.4
• Diagnostic Category: lint/suspicious/noDuplicateProperties
• This rule is recommended, which means is enabled by default.
• This rule doesn’t have a fix.
• The default severity of this rule is error.
• Sources:
  • Same as stylelint/declaration-block-no-duplicate-properties

How to configure

biome.json

{
  "linter": {
    "rules": {
      "suspicious": {
        "noDuplicateProperties": "error"
      }
    }
  }
}

Description

Disallow duplicate properties within declaration blocks.

This rule checks the declaration blocks for duplicate properties. It ignores custom properties.

Examples

Invalid

a {
  color: pink;
  color: orange;
}

code-block.css:3:3 lint/suspicious/noDuplicateProperties ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Duplicate properties can lead to unexpected behavior and may override previous declarations unintentionally.
  
    1 │ a {
    2 │   color: pink;
  > 3 │   color: orange;
      │   ^^^^^
    4 │ }
    5 │ 
  
  ℹ color is already defined here.
  
    1 │ a {
  > 2 │   color: pink;
      │   ^^^^^
    3 │   color: orange;
    4 │ }
  
  ℹ Remove or rename the duplicate property to ensure consistent styling.
  

Valid

a {
  color: pink;
  background: orange;
}

Related links

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