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CSS Selector Specificity Calculator
x402
CSS Selector Specificity Calculator is a paid API for AI agents from css-design-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).
Calculates CSS selector specificity (IDs, classes, types) per Selectors Level 4, including :is(), :not(), :where(), and :has(), and optionally compares two selectors to determine which wins in the cascade.
Price / call$0.02
Success—
StatusUnknown
How this service works
CSS selector specificity (ids, classes, types) per Selectors Level 4, including :is(), :not(), :where() and :has(); compare two.
Output
Returns a structured object containing per-selector specificity breakdowns (a/b/c triple, ID count, class count, type count, formatted specificity string), a summary, and if a second selector is provided, a comparison object indicating which selector wins in the cascade, why, and the detail explanation. Also includes validity flags, any selectors not checked, and disclaimers.
Example use cases
Debug overriding CSS rule
“My rule .card .title isn't applying — can you calculate the specificity of .card .title and compare it to #sidebar .title so I know which one wins in the cascade?”
Validate :is() and :where() specificity
“I'm using :is(nav, header) ul > li a and :where(nav, header) ul > li a — can you calculate the specificity of both so I understand how :where() changes things?”
Audit complex selector before shipping
“Before I ship this stylesheet, can you tell me the specificity breakdown — IDs, classes, types — for the selector body.theme-dark main > article.post:not(.draft) h2?”
Technical details
Endpoint
GEThttps://css-design-calc.x402tookit.com/css-specificity?utm_source=zero.xyzWhen to prefer
Use this endpoint when you need programmatic, standards-compliant CSS specificity computation per Selectors Level 4, especially when working with modern pseudo-classes like :is(), :not(), :where(), and :has() that have non-obvious specificity behavior. Prefer this over manual calculation for complex selectors or when debugging cascade conflicts between two competing rules.
Side effects
- Invalid or unparseable selector returns valid:false with reasons array explaining parse errors
- Unsupported pseudo-classes may appear in notChecked array
- Malformed comma-separated selector list may result in partial results
- Missing required selector query parameter returns an error response
- Very complex or deeply nested selectors may produce degraded:true with partial results
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Tags
x402
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