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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds genuine context beyond that by revealing the data comes from PageSpeed Insights as point-in-time snapshots across two device categories, but it says nothing about latency, rate limits, or freshness.

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 that front-loads the resource and metric list before the source and scope. No filler, no redundancy.

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 one-parameter read tool with no output schema, the description usefully enumerates the returned metrics (LCP, CLS, INP, FCP, TTFB) and the two device scopes, so the agent knows what comes back. Only minor gaps remain around freshness and any precondition for the site_id.

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?

There is a single parameter with 100% schema description coverage, so the schema already documents site_id fully. The description adds no format, identifier, or validation detail beyond what the schema provides, making the baseline 3 appropriate.

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 (Core Web Vitals, enumerated as LCP, CLS, INP, FCP, TTFB), the data source (PageSpeed Insights), and the scope (mobile + desktop snapshots). This clearly separates it from metric siblings like get_gsc_metrics or get_bing_metrics, though it never names an alternative 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 when-to-use or when-not guidance and no mention of prerequisites (e.g., whether the site must be scanned first) or alternatives. The agent must infer usage purely from the tool name and metric list.

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