CSS Houdini is a family of browser APIs that lets developers work with parts of the CSS engine. The easiest place to start is @property, which gives a custom property a declared type, inheritance rule, and initial value. Paint Worklets go further by generating CSS images with JavaScript, but support varies by API: check each feature in the browsers you need to serve.
What is CSS Houdini?
Houdini is an umbrella term for APIs that expose parts of the browser’s CSS processing and rendering behavior. Some APIs make custom properties more expressive; others provide typed JavaScript interfaces to CSS values or let a worklet generate an image for CSS to use. Houdini is not one feature, and it does not let developers add arbitrary CSS syntax in every browser. See MDN’s Houdini APIs overview and its CSS Houdini guide.
Start with a typed custom property using @property
Ordinary custom properties hold token sequences; CSS does not necessarily know whether a value is intended to be a number, color, or another type. The Properties and Values API lets you register a custom property with a syntax, inheritance behavior, and initial value:
@property --progress {
syntax: "<number>";
inherits: false;
initial-value: 0;
}
.progress-ring {
--progress: 0.65;
}This declares behavior for the author-named --progress property; it does not create a new built-in CSS property. The registration tells the browser how to parse and validate its value. The required fields are syntax, inherits, and initial-value. Read MDN’s Properties and Values API guide.
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Registering from JavaScript
You can register the same kind of property with CSS.registerProperty() when registration belongs in script setup rather than a stylesheet:
CSS.registerProperty({
name: "--progress",
syntax: "<number>",
inherits: false,
initialValue: 0
});Choose CSS @property when the declaration naturally belongs with your styles. Use the JavaScript method when registration is part of your script initialization. See the API reference.
Generate a CSS image with a Paint Worklet
The CSS Painting API lets JavaScript in a Paint Worklet produce an image value that CSS can use with paint(name), often as a background. A page loads the module with CSS.paintWorklet.addModule(); the module registers a painter whose paint method receives the output dimensions and can use declared CSS properties as inputs. Refer to MDN’s CSS Painting API documentation and the paint() reference.
For example, this painter draws diagonal stripes. Save the following as stripes.js:
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registerPaint("stripes", class {
static get inputProperties() {
return ["--stripe-color"];
}
paint(ctx, size, properties) {
const color = properties.get("--stripe-color").toString().trim() || "#4677cc";
ctx.fillStyle = color;
ctx.fillRect(0, 0, size.width, size.height);
ctx.strokeStyle = "rgba(255, 255, 255, 0.75)";
ctx.lineWidth = 4;
for (let x = -size.height; x < size.width; x += 18) {
ctx.beginPath();
ctx.moveTo(x, 0);
ctx.lineTo(x + size.height, size.height);
ctx.stroke();
}
}
});Load it after the document is available, and provide a conventional CSS fallback first:
.pattern {
--stripe-color: #4677cc;
background: repeating-linear-gradient(
135deg,
#4677cc 0 12px,
#7898d3 12px 24px
);
}
@supports (background: paint(stripes)) {
.pattern {
background: paint(stripes);
}
}
if ("paintWorklet" in CSS) {
CSS.paintWorklet.addModule("stripes.js").catch((error) => {
console.error("Could not load the stripes paint worklet", error);
});
}The fallback remains in place where the worklet is unavailable or the @supports condition is false. The CSS feature query checks support for the paint value, while the JavaScript guard avoids calling an unavailable paintWorklet property. Serve the module from an origin and in a configuration permitted by the browser; if it fails to load, the fallback background still provides a usable result. Worklet syntax and availability are browser-dependent, so validate the exact implementation in target browsers using the API documentation.
Use generated paint for decorative effects, not for essential text or controls. The available documentation explains how to use the API; it does not establish a general speed advantage over ordinary CSS backgrounds.
Other Houdini APIs and where they fit
| API area | What it does | Practical use |
|---|---|---|
| Properties and Values | Registers custom-property syntax, inheritance, and initial values through @property or CSS.registerProperty(). |
A practical first experiment; MDN marks the API Baseline 2024. |
| CSS Painting | Uses Paint Worklets to generate image values consumed by paint(). |
Generated backgrounds and patterns, with a fallback for unsupported browsers. |
| CSS Typed OM | Represents CSS values as typed JavaScript objects and exposes structured style maps. | Useful when scripts need structured values rather than manually parsing strings; availability is limited. |
| CSS Layout API | Would let authors define layout algorithms. | Treat as work in progress, not a general-purpose production feature. |
| CSS Parser API | Proposes direct access to CSS parsing concepts. | MDN describes it as a proposal with no browser implementation in its overview. |
| Font Metrics API | Would expose font metrics and layout information. | MDN describes it as a proposal with no browser implementation in its overview. |
See the MDN overview, Typed OM API reference, and the W3C CSS Layout API Level 1 document. The W3C document says, “It is inappropriate to cite this document as other than work in progress.” A published draft is not proof that a feature is finished or interoperable.
Best Value
Use CSS Typed OM for structured style values
The CSS Typed Object Model represents CSS values with typed JavaScript objects. For example, a CSSUnitValue keeps a numeric value and its unit separate; style maps provide structured access to declarations or computed styles. That can make style manipulation clearer where scripts would otherwise construct or parse strings. MDN marks Typed OM as not Baseline and of limited availability, so check the API reference and guide before relying on it.
Check support and choose a safe fallback
There is no single answer to whether “Houdini is supported”: browser support is API-specific. As of October 3, 2026, MDN identifies the Properties and Values API as Baseline 2024, newly available across the latest devices and browser versions since July 2024. Older browsers and devices may still lack it. MDN marks Painting and Typed OM as not Baseline because they do not work in some widely used browsers. Check the relevant compatibility tables for the specific API and test your actual browser, device, and webview targets: Properties and Values, Painting, and Typed OM.
Baseline is a cross-browser availability summary, not a substitute for testing older devices, usability, accessibility, performance, or security. MDN explains the term in its Baseline compatibility glossary.
- Use ordinary CSS as a fallback for optional Paint Worklet effects.
- Do not make essential information or functionality depend on a generated image.
- Check browser compatibility and test the exact browsers you support before shipping.
- Prefer an existing standard CSS feature when it solves the problem with less complexity.
- Do not infer that a Layout API or other proposal is deployable merely because a specification page exists.
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