# CSS (Cascading Style Sheets)

> CSS is a W3C web standard describing the presentation of HTML and XML documents — layout,
> colors, typography and animation. It is defined by the W3C CSS Working Group across 101
> specification modules and implemented natively by every major browser. CSS itself is a
> specification, not a hosted product: there is no CSS API to call. The one callable surface
> in this record is the W3C CSS Validation Service, which checks a stylesheet against a CSS
> profile.

Generated 2026-09-07 by the API Evangelist enrichment pipeline from this record and from
documents fetched live from w3.org and jigsaw.w3.org. Method: generated. No /llms.txt is
served by w3.org, drafts.csswg.org or jigsaw.w3.org (all 404 on 2026-09-07).

## The standard

- [CSS at W3C](https://www.w3.org/Style/CSS/): The CSS Working Group's home page.
- [CSS Specifications (W3C TR)](https://www.w3.org/TR/?tag=css): Every published CSS module.
- [CSS Current Work](https://www.w3.org/Style/CSS/current-work): Which modules exist and what maturity each has reached.
- [CSS Snapshot 2026](https://www.w3.org/TR/css-2026/): W3C's definition of what "CSS" contains this year — the thing to pin to rather than individual module levels.
- [CSS Editor's Drafts](https://drafts.csswg.org/): Continuously rebuilt working copies of every module.
- [CSS 2.2 Specification](https://www.w3.org/TR/CSS22/)
- [CSS Working Group](https://www.w3.org/groups/wg/css/): Charter, participants and process.
- [MDN CSS Reference](https://developer.mozilla.org/en-US/docs/Web/CSS): Third-party (Mozilla), not W3C.

## Machine-readable CSS

- [All CSS properties (JSON)](https://www.w3.org/Style/CSS/all-properties.en.json): 731 distinct properties, each with its defining specification, definition anchor and W3C maturity status. Saved in this record at `vocabulary/css-all-properties.json`.
- [All at-rule descriptors (JSON)](https://www.w3.org/Style/CSS/all-descriptors.en.json): 92 descriptors. Saved at `vocabulary/css-all-descriptors.json`.
- [@webref/css](https://www.npmjs.com/package/@webref/css): Per-specification JSON extracts of every property, at-rule, selector and value, generated by W3C from the specs themselves.
- [@webref/idl](https://www.npmjs.com/package/@webref/idl): Web IDL for the CSSOM and CSS Houdini interfaces.
- [web-specs](https://www.npmjs.com/package/web-specs): Curated index of every web specification including each CSS module.

## The CSS Validation Service (the callable API)

- [Service home and console](https://jigsaw.w3.org/css-validator/): Validate by URL, file upload, or direct input. No account.
- [Web Service API documentation](https://jigsaw.w3.org/css-validator/api.html): SOAP 1.2 interface and response format.
- [User Manual — request format](https://jigsaw.w3.org/css-validator/manual.html#requestformat): The full parameter table.
- [WSDL 2.0 description](https://www.w3.org/2005/09/css-validator.wsdl): The machine-readable contract. Saved at `wsdl/css-validator.wsdl`.
- Base URL: `https://jigsaw.w3.org/css-validator/validator`
- Authentication: none. Anonymous, free, public.
- Rate limit: sleep at least 1 second between programmatic requests. There are no rate-limit response headers.
- Watch out: an invalid stylesheet returns HTTP 200 with `validity: false`. Validation errors are not call failures.

## Source and tooling

- [w3c/csswg-drafts](https://github.com/w3c/csswg-drafts): Specification source and issue tracker.
- [w3c/css-houdini-drafts](https://github.com/w3c/css-houdini-drafts): Houdini extensibility specs.
- [w3c/css-validator](https://github.com/w3c/css-validator): The validator source, in Java.
- [Download the validator](https://jigsaw.w3.org/css-validator/DOWNLOAD.html): Run it yourself — `java -jar css-validator.jar <url>`. Recommended over calling the public service in volume.
- [web-platform-tests/wpt css](https://github.com/web-platform-tests/wpt/tree/master/css): The CSS conformance test suite.
- [wpt.fyi CSS results](https://wpt.fyi/results/css): Cross-browser implementation results.

## Governance and licensing

- [W3C Process Document](https://www.w3.org/policies/process/): The maturity ladder, and the Superseded / Obsolete / Rescinded end-of-life states for a Recommendation.
- [W3C Patent Policy](https://www.w3.org/policies/patent-policy/): Royalty-free licensing of essential claims. This is why CSS costs nothing to implement.
- [W3C Document License](https://www.w3.org/copyright/document-license/)
- [W3C Privacy Policy](https://www.w3.org/policies/privacy/)
- [W3C Status](https://status.w3.org/): Incident status for W3C services.

## Optional

- [www-style mailing list archive](https://lists.w3.org/Archives/Public/www-style/): Public CSS discussion.
- Validator feedback: www-validator-css@w3.org

## Not published

Checked on 2026-09-07 and absent: no OpenAPI, no AsyncAPI, no GraphQL, no event or webhook
surface, no MCP server, no A2A agent card, no OAuth, no `/.well-known/` documents on any host,
no security.txt, no trust center, no paid plans.