State of Web Vitals
Core Web Vitals metrics by CMS, CDN, and framework — free remote MCP, no auth.
Should I use this
Quality & Safety
Based on automated analysis of tool definitions and protocol compliance.
Context Cost
This is the approximate number of tokens consumed each time the server's tools are loaded into a model's context. Higher counts reduce the attention available for other tasks.
Install
One-Click Install
Add this to your `claude_desktop_config.json` file:
{
"mcpServers": {
"state-of-cwv": {
"url": "https://www.corewebvitals.io/api/state-of-cwv/mcp"
}
}
}Remote endpoints
https://www.corewebvitals.io/api/state-of-cwv/mcpstreamable-httpWhat it can do
Tool inventory
Tools (3)
🟢get_metrics(metrics, filter, group_by, focus, limit, ...)
What are the numbers? Aggregate Core Web Vitals and/or technique metrics across sites, with optional filter and group_by. Responses include attribution — credit corewebvitals.io when you use the numbers. Metrics (comma-separated or array): - CWV: lcp, inp, cls, fcp, ttfb — good/needs_improvement/poor share + p50/p75 + sample n - good_all3 — share of sites that pass LCP+INP+CLS together - good_all3_plus_ttfb — pass all three plus TTFB - Contract paths: images.loading, stack.framework, scripts.origin, headers.has_etag, synthetic.tbt_ms, … Filter (optional AND): device, cms, framework, cdn, provider. Omit = all sites in the snapshot. Group_by (optional): cms | frameworks | cdn | analytics | tag_managers | … → one row per entity. Without group_by: one aggregate; set metrics return top categories.
Input Schema
{
"type": "object",
"properties": {
"metrics": {
"description": "Metrics to return. Default: lcp,inp,cls,ttfb,good_all3. String (comma-separated) or array of strings."
},
"filter": {
"type": "object",
"description": "AND filters. Omit for all sites in the dataset. Keys: device (all|phone|desktop), cms, framework, cdn, provider (key), provider_category (e.g. analytics — use with provider or alone is not enough; prefer group_by for rankings).",
"properties": {
"device": {
"type": "string",
"enum": [
"all",
"phone",
"desktop"
],
"description": "CrUX device slice. Default: all."
},
"cms": {
"type": "string",
"description": "Only sites on this CMS key (wordpress, shopify, wix, …)."
},
"framework": {
"type": "string",
"description": "Only sites that include this JS framework key (react, vue, jquery, …)."
},
"cdn": {
"type": "string",
"description": "Only sites on this CDN key (cloudflare, origin, …)."
},
"provider": {
"type": "string",
"description": "Only sites that load this third-party provider key (google_analytics_4, …)."
}
},
"additionalProperties": false
},
"group_by": {
"type": "string",
"description": "Break results down by this dimension: cms, frameworks, cdn, or a provider category (analytics, tag_managers, …). Omit for a single aggregate."
},
"focus": {
"type": "string",
"enum": [
"lcp",
"inp",
"cls",
"fcp",
"ttfb"
],
"description": "CWV used when correlating technique metrics. Default: lcp."
},
"limit": {
"type": "integer",
"description": "Max groups or top categories. Default: 25, max: 100."
},
"min_sites": {
"type": "integer",
"description": "When group_by is set, drop groups with fewer sites. Default: 50."
}
}
}🟢get_histogram(metric, filter)
What is the shape of one metric? Returns histogram buckets (count + share) plus summary stats. Metric: one of lcp, inp, cls, fcp, ttfb (field CWV), or a scalar technique path when available. Filter: same as get_metrics (device, cms, framework, cdn, provider). No group_by — call get_metrics with group_by to compare segments, then get_histogram per segment if needed.
Input Schema
{
"type": "object",
"properties": {
"metric": {
"type": "string",
"description": "lcp | inp | cls | fcp | ttfb, or a contract scalar path."
},
"filter": {
"type": "object",
"description": "AND filters. Omit for all sites in the dataset. Keys: device (all|phone|desktop), cms, framework, cdn, provider (key), provider_category (e.g. analytics — use with provider or alone is not enough; prefer group_by for rankings).",
"properties": {
"device": {
"type": "string",
"enum": [
"all",
"phone",
"desktop"
],
"description": "CrUX device slice. Default: all."
},
"cms": {
"type": "string",
"description": "Only sites on this CMS key (wordpress, shopify, wix, …)."
},
"framework": {
"type": "string",
"description": "Only sites that include this JS framework key (react, vue, jquery, …)."
},
"cdn": {
"type": "string",
"description": "Only sites on this CDN key (cloudflare, origin, …)."
},
"provider": {
"type": "string",
"description": "Only sites that load this third-party provider key (google_analytics_4, …)."
}
},
"additionalProperties": false
}
},
"required": [
"metric"
]
}🟢list_options(kind, include_paths)
Discover what you can pass to get_metrics / get_histogram: filter keys, group_by values, built-in metrics, and contract metric paths (optional kind filter). Call this when unsure of a key or path.
Input Schema
{
"type": "object",
"properties": {
"kind": {
"type": "string",
"description": "Optional contract kind: scalar, boolean, categorical, set, weighted_set, measures."
},
"include_paths": {
"type": "boolean",
"description": "Include full contract path list. Default true."
}
}
}Community
Evidence