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valid-speculation-rules

Validate the body of <script type="speculationrules"> elements against HTML Living Standard § 7.6 Speculation rules (the feature originated as the WICG nav-speculation draft, which now redirects to the HTML Standard). type attribute matching is ASCII case-insensitive, matching how user agents look up the script's effective MIME type.

Split out of the former script-content rule, alongside valid-importmap for type="importmap".

The rule reports the following issues for inline speculation rules:

  • The element body is empty, whitespace-only, or cannot be parsed as JSON
  • The top-level value is not a JSON object, or has no prefetch or prerender property
  • A top-level key other than tag, prefetch, or prerender is present
  • A prefetch / prerender value is not a JSON array, or a rule in it is not a JSON object
  • A rule has a key other than source, urls, where, relative_to, eagerness, referrer_policy, tag, requires, expects_no_vary_search, or target_hint
  • source is not a string, or is a value other than list or document
  • A list rule (explicit or inferred from urls) is missing urls, or has a where
  • A document rule (explicit or inferred from where) is missing where, or has urls
  • A rule has no source and its source cannot be inferred (it has neither urls nor where, or has both)
  • urls is not a JSON array, is empty, or contains a non-string or empty-string item
  • eagerness is not a string, or is a value other than immediate, eager, moderate, or conservative
  • where is not a JSON object, or does not contain exactly one predicate (and, or, not, href_matches, or selector_matches)
  • An and / or predicate is not a JSON array, or is empty
  • An href_matches / selector_matches pattern is not a string or an array of strings, is empty, or contains an empty-string item

❌ Examples of incorrect code for this rule

<script type="speculationrules">
  {
    "prefetch": [{ "source": "list" }]
  }
</script>
<script type="speculationrules">
  {
    "prefetch": [{ "source": "document", "where": {} }]
  }
</script>

✅ Examples of correct code for this rule

<script type="speculationrules">
  {
    "prefetch": [
      {
        "source": "document",
        "where": {
          "and": [{ "href_matches": "/*" }, { "not": { "selector_matches": ".no-prefetch" } }]
        },
        "eagerness": "moderate"
      }
    ],
    "prerender": [{ "source": "list", "urls": ["/next"] }]
  }
</script>

Interface​

{
  "valid-speculation-rules": boolean
}

Validate the body of <script type="speculationrules"> elements against the Speculation Rules spec.

Default Severity​

error