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

With no annotations, the description carries the full burden and does useful work: it discloses the field-data caveat, the single-page scope, and the not_measured sentinel semantics for missing lab metrics. It omits operational traits like rate limits and PSI call latency, which would be relevant for a remote measurement tool.

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?

Four short sentences, each front-loading a distinct constraint (scope, field data, site scope, sentinel value) with zero filler. The scope limitation leads the description, which is the right priority.

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 measurement tool with no annotations and no output schema, the description covers scope, data-source caveats, and the missing-metric convention. It does not describe the shape of the returned metrics, but with only two simple parameters the definition is largely complete.

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 coverage is 50%: url is documented in the schema and strategy is an enum that is largely self-explanatory. The description adds no format or constraint detail for either parameter, so with half the schema documented the baseline of 3 is 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?

States a specific verb ('check') plus resource ('Core Web Vitals') and names the data source (PageSpeed Insights) and scope ('one URL and one strategy'). This distinguishes it from audit_page and crawl_site, which cover broader auditing.

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?

Explicitly bounds usage with two negative statements: it does not measure field/CrUX data and does not audit the rest of the site, implying the sibling crawlers/auditors are the right tools for those jobs. It stops short of naming the alternative tool explicitly, so it falls just below a 5.

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