Sharelint

Check performance

check_performance

Read-onlyIdempotent

Check what slows a URL down, without running a browser. Times the server response as a regular browser (time to first byte, compression, caching, redirects, HTTP/3), reads the HTML for render-blocking scripts and stylesheets, third-party scripts, the main image (lazy loading, preload, weight), images without width and height, and font loading, and reports real-user Core Web Vitals (LCP, INP, CLS) on phones from the Chrome UX Report when Google has data. Returns a score and copy-ready fixes. Use it for questions like "why is my site slow" or "how do I improve my Core Web Vitals".

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "url": "<url>"
    },
    "name": "check_performance"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes	Public http(s) URL or bare domain to check, for example "example.com/pricing". Private and local addresses are refused.

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 11, 2026

TDQS

A4.1/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly, idempotent and non-destructive behavior, so the bar is lower, yet the description adds real value: no browser is launched, Core Web Vitals come from the Chrome UX Report and are only present "when Google has data", and the response includes a score plus copy-ready fixes. That conditional-data caveat is the kind of context annotations cannot express.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The key distinction ("without running a browser") is front-loaded, followed by a dense enumeration of checks and a closing usage hint. The middle sentence is long and list-heavy, but each item names a distinct signal, so little is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description must carry the return contract, and it does: a score plus copy-ready fixes. Methodology, data-source conditioning and the public-URL constraint are all covered; only runtime or pagination-style expectations are absent, which is minor for a read-only audit.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

There is a single parameter with 100% schema description coverage, including the note that private and local addresses are refused. The description adds no syntax or format detail beyond the schema, so the baseline of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and outcome ("Check what slows a URL down") and then enumerates the exact signals measured: TTFB, compression, caching, redirects, HTTP/3, render-blocking scripts/stylesheets, third-party scripts, image loading, and Core Web Vitals. This scope is clearly distinct from the nearby check_url and check_ai_visibility siblings.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives concrete triggering questions ("why is my site slow", "how do I improve my Core Web Vitals"), which tells an agent when to select this tool. It does not explicitly exclude or compare against alternative tools, so 4 rather than 5.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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