Chrome UX Report: Core Web Vitals reali

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

Annotations only supply readOnlyHint and openWorldHint, so the description carries the rest and does so well: it discloses the 28-day aggregation window, the 75th-percentile basis, the good/needs-improvement/poor judgment bands, and the presence of a distribution, plus the ranking-relevance motive. It stops short of stating rate limits or that some URLs lack data, but it adds substantial behavioral context beyond the annotations.

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

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

A single dense sentence front-loads the core identity and then enumerates metrics, percentile, verdicts, and distribution without wasted words. The trailing ranking-relevance sentence is short and earns its place as motivation, though the parenthetical listing is slightly cluttered.

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

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

For a read-only query tool with no output schema, the description usefully previews the return shape (metrics, 75th percentile, judgement, distribution), so an agent knows what comes back. Combined with full schema coverage on the inputs, it is nearly complete; only the explicit sibling routing (vs crux_history/psi_analyze) is missing.

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

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

Schema description coverage is 100%, so the schema already fully documents url, origin, and formFactor (including the mobile default rationale). The description adds nothing about the parameters, which is acceptable given the coverage but means the baseline of 3 is the correct ceiling here.

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

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

The description names the specific resource (real-user Chrome Core Web Vitals for the last 28 days) and the exact metrics returned (LCP, INP, CLS, FCP, TTFB), so an agent knows precisely what data it gets. It implicitly separates itself from crux_history via the '28 giorni' window, but never names or contrasts with the sibling explicitly.

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

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

There is no explicit when-to-use or when-not-to-use guidance. The line 'Sono i dati che Google usa per il ranking' hints at a use case (assessing ranking-relevant page experience), but it never says how this differs from crux_history or psi_analyze, which are the obvious alternatives in the sibling list.

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