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

Annotations already declare readOnlyHint, openWorldHint, and destructiveHint, so the safety profile is covered. The description adds genuinely useful context beyond that: no account/auth required and a one-hour result cache, which an agent should know before re-running.

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?

Front-loaded with the core action, followed by a dense but informative enumeration of return values. The return-value list is long but earns its place given there is no output schema.

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?

With no output schema, the description carries the return-value burden and does so thoroughly, enumerating Lighthouse scores, CrUX metrics, and opportunities. The main gap is the absence of guidance distinguishing it from overlapping sibling tools.

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 url and strategy parameters are fully documented in the schema, setting the baseline at 3. The description adds no syntax or format detail beyond the schema; the phrase 'for the page or the whole site' is ambiguous and not tied to a parameter.

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?

States a specific verb (run) and resource (Google PageSpeed Insights) on a URL, so an agent immediately knows the operation. However, it does not distinguish itself from closely related siblings like check_core_web_vitals or get_page_score, which the description's own mention of Core Web Vitals data overlaps with.

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?

The description says nothing about when to choose this tool over the overlapping check_core_web_vitals or get_page_score siblings. It implies 'run this on a URL' but provides no conditions, exclusions, or alternative routing.

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