---
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title: noUnknownProperty
description: Learn more about noUnknownProperty
---
import { Tabs, TabItem } from '@astrojs/starlight/components';

<Tabs>
<TabItem label="CSS" icon="seti:css">
## Summary
- Rule available since: `v1.8.0`
- Diagnostic Category: [`lint/correctness/noUnknownProperty`](/reference/diagnostics#diagnostic-category)
- This rule is **recommended**, meaning it is enabled by default.
- This rule doesn't have a fix.
- The default severity of this rule is [**error**](/reference/diagnostics#error).
- Sources: 
  - Same as [`property-no-unknown`](https://github.com/stylelint/stylelint/blob/main/lib/rules/property-no-unknown/README.md)

## How to configure
```json title="biome.json"
{
	"linter": {
		"rules": {
			"correctness": {
				"noUnknownProperty": "error"
			}
		}
	}
}

```
## Description
Disallow unknown properties.

This rule considers properties defined in the CSS Specifications and browser specific properties to be known.
https://github.com/known-css/known-css-properties#source

This rule ignores:

- custom variables e.g. `--custom-property`
- vendor-prefixed properties (e.g., `-moz-align-self,` `-webkit-align-self`)

## Examples

### Invalid

```css
a {
  colr: blue;
}
```

<pre class="language-text"><code class="language-text">code-block.css:2:3 <a href="https://biomejs.dev/linter/rules/no-unknown-property">lint/correctness/noUnknownProperty</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━<br /><br />  <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">Unknown property is not allowed.</span><br />  <br />    <strong>1 │ </strong>a &#123;<br />  <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong>  colr: blue;<br />   <strong>   │ </strong>  <strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><br />    <strong>3 │ </strong>&#125;<br />    <strong>4 │ </strong><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">See </span><span style="color: lightgreen;"><a href="https://stylelint.io/user-guide/rules/property-no-unknown/">CSS Specifications and browser specific properties</a></span><span style="color: lightgreen;"> for more details.</span><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">To resolve this issue, replace the unknown property with a valid CSS property.</span><br />  <br /></code></pre>

```css
a {
  my-property: 1;
}
```

<pre class="language-text"><code class="language-text">code-block.css:2:3 <a href="https://biomejs.dev/linter/rules/no-unknown-property">lint/correctness/noUnknownProperty</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━<br /><br />  <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">Unknown property is not allowed.</span><br />  <br />    <strong>1 │ </strong>a &#123;<br />  <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong>  my-property: 1;<br />   <strong>   │ </strong>  <strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><br />    <strong>3 │ </strong>&#125;<br />    <strong>4 │ </strong><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">See </span><span style="color: lightgreen;"><a href="https://stylelint.io/user-guide/rules/property-no-unknown/">CSS Specifications and browser specific properties</a></span><span style="color: lightgreen;"> for more details.</span><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">To resolve this issue, replace the unknown property with a valid CSS property.</span><br />  <br /></code></pre>

### Valid

```css
a {
  color: green;
}
```

```css
a {
  fill: black;
}
```

```css
a {
  -moz-align-self: center;
}
```

## Related links

- [Disable a rule](/linter/#disable-a-rule)
- [Configure the code fix](/linter#configure-the-code-fix)
- [Rule options](/linter/#rule-options)
- [Source Code](https://github.com/biomejs/biome/blob/main/crates/biome_css_analyze/src/lint/correctness/no_unknown_property.rs)
- [Test Cases](https://github.com/biomejs/biome/blob/main/crates/biome_css_analyze/tests/specs/correctness/noUnknownProperty)

</TabItem>
</Tabs>