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

Annotations already declare readOnlyHint=false, destructiveHint=true, openWorldHint=true, and idempotentHint=false, so the safety profile is largely carried by structured metadata. The description adds only that it uses 'real PageSpeed Insights data' (a live external call), but never reconciles with the 'destructive' annotation, mentions latency/rate limits, or says whether results are persisted — an agent could reasonably mistake this for a harmless read.

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 sentence that front-loads the verb, enumerates the metrics, and names the data source. No filler and nothing buried.

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?

There is no output schema, so the description's listing of the five metrics partially covers what comes back, which is useful. However, it omits how to choose between this and get_cwv_results, and says nothing about result persistence, timing, or the meaning of the destructive/openWorld annotations.

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 url, site_id, and strategy (with its mobile/desktop default) are fully documented in the schema. The description adds no parameter-level meaning beyond naming the measured metrics, so the baseline of 3 applies.

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 ('Measure'), a concrete resource ('Core Web Vitals (LCP, FID, CLS, INP, TTFB)'), its scope ('for a URL'), and its data source ('real PageSpeed Insights data'). It does not explicitly differentiate itself from the sibling get_cwv_results, which appears to retrieve stored measurements, so it falls short of a 5.

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 never states when to use this tool versus alternatives such as get_cwv_results, get_site_health, or inspect_url, nor any prerequisites or exclusions. It only says what the tool does, leaving all routing decisions to inference.

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