generated: '2026-09-07'
method: searched
source: >-
  https://jigsaw.w3.org/css-validator/manual.html#requestformat and
  https://jigsaw.w3.org/css-validator/api.html, cross-checked against
  wsdl/css-validator.wsdl
api: W3C CSS Validation Service
summary: >-
  Cross-cutting runtime semantics for the one callable surface in this record. The service is
  a single-operation, read-only validator: one endpoint, seven query parameters, five
  response serializations, no state and no writes.
base_url: https://jigsaw.w3.org/css-validator/validator
auth_style:
  model: anonymous
  detail: No credentials. See authentication/css-authentication.yml.
request:
  style: query-parameters
  methods: [GET, POST]
  parameters:
    - name: uri
      required: conditional
      default: null
      description: URL of the document to validate. HTML or CSS. Either uri or text must be given.
    - name: text
      required: conditional
      default: null
      description: The stylesheet to validate inline. CSS only. Either uri or text must be given.
    - name: usermedium
      required: false
      default: all
      description: 'The @media context to validate against: screen, print, braille and others.'
    - name: output
      required: false
      default: html
      description: Response serialization. See the response block below.
    - name: profile
      required: false
      default: css2
      description: >-
        CSS profile to validate against — css1, css2, css21, css3, svg, svgbasic, svgtiny,
        mobile, atsc-tv, tv, none.
    - name: lang
      required: false
      default: en
      description: >-
        Language of the human-readable messages — en, fr, it, ko, ja, es, zh-cn, nl, de, pl.
    - name: warning
      required: false
      default: '2'
      description: >-
        Warning verbosity — "no" for none, 0 for fewer, 1 or 2 for more. Warnings are advisory
        and do not affect validity.
response:
  content_negotiation: >-
    By query parameter, not by Accept header. The output parameter selects the serialization
    and the service sets Content-Type to match.
  formats:
    - value: html / text/html
      content_type: text/html
      note: XHTML document. The default.
    - value: xhtml / application/xhtml+xml
      content_type: application/xhtml+xml
    - value: soap12 / application/soap+xml
      content_type: application/soap+xml
      note: >-
        The interface described by wsdl/css-validator.wsdl. Envelope namespace
        http://www.w3.org/2003/05/soap-envelope, payload namespace
        http://www.w3.org/2005/07/css-validator.
    - value: text / text/plain
      content_type: text/plain
    - value: json
      content_type: application/json
      note: >-
        Not listed in the User Manual parameter table, but observed live on 2026-09-07:
        output=json returns a cssvalidation object mirroring the SOAP response
        (uri, checkedby, csslevel, date, timestamp, validity, result.errorcount,
        result.warningcount). Recorded as probed, not as documented.
  envelope:
    root: cssvalidationresponse (SOAP) / cssvalidation (JSON)
    fields:
      - uri — the document validated; the EARL TestSubject
      - checkedby — the service that produced the result; the EARL Assertor
      - csslevel — the profile in force during validation
      - date — validation timestamp
      - validity — boolean pass/fail
      - result — errors and warnings, each with count and list
versioning:
  scheme: none
  detail: >-
    The endpoint carries no version segment and no version header. What varies is the CSS
    profile being validated against, selected per request by the profile parameter, and the
    build of the validator W3C happens to be running. The DOWNLOAD page warns explicitly
    that the online service is a stable release, generally older than the Git version, and
    that results and behaviour may differ — so a caller cannot pin the engine version.
  source: https://jigsaw.w3.org/css-validator/DOWNLOAD.html
pagination:
  style: none
  detail: A validation response returns the complete error and warning lists for one document.
expansion:
  supported: false
metadata:
  supported: false
request_id:
  header: null
  detail: >-
    No request or correlation identifier is returned. The nearest thing to a trace handle is
    the echoed uri plus the date/timestamp fields in the response body.
rate_limit_signaling:
  headers: []
  detail: >-
    No rate-limit headers. A documented one-second courtesy interval only. See
    rate-limits/css-rate-limits.yml.
error_envelope:
  format: domain-specific
  detail: >-
    Not RFC 9457. Validation failures are not HTTP errors — an invalid stylesheet returns 200
    with validity false and a populated errorlist. See errors/css-problem-types.yml.
idempotency:
  coverage: na
  mechanism: none
  detail: >-
    The service has no write surface. Every request is a pure function of the submitted
    document and parameters, so replaying one costs nothing and changes nothing. There is no
    Idempotency-Key header and none is needed; no Idempotency pointer is emitted for this
    record.
reversibility:
  grade: na
  detail: >-
    Read-only. No operation creates, mutates or destroys anything on the provider's side, so
    there is nothing to reverse and no reversal window to state. Marked na rather than scored
    zero.
  write_surfaces: []
dry_run_mode:
  supported: na
  detail: >-
    Not applicable for the same reason as reversibility — the entire service is already a
    rehearsal surface. Validating a stylesheet is itself the no-effect check an agent would
    otherwise want a dry run for.
cross_references:
  - authentication/css-authentication.yml
  - rate-limits/css-rate-limits.yml
  - errors/css-problem-types.yml
  - lifecycle/css-lifecycle.yml
  - wsdl/css-validator.wsdl