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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive). Beyond that the description discloses non-obvious behavior: metric caveats, that p75 figures may be approximate, that some metrics depend on browser/interaction sampling, and the available:false failure mode. It does not cover pagination or response size, keeping it below 5.

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?

The core purpose is front-loaded, but the body is a single dense wall of text enumerating every metric, sub-field and rating threshold. Much of that is valuable given no output schema, but the run-on sentence structure hurts scannability and some detail borders on restating what a caller will observe.

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 and seven parameters, the description compensates well by describing the return shape (metrics, p75, rating, by_device, previous, change, page_loads, statuses) and the error path. It is close to complete for an agent deciding whether to call it and what to expect.

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 documents every parameter, and the description largely defers ('as for get_site_summary', 'as get_site_summary's range says'). It adds one genuinely useful constraint — that goal/entry/exit filters are invalid here — but otherwise adds little beyond the schema, so the baseline 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?

The first clause states a specific resource and scope ('how fast a site's pages were over a range... beside the period before'), which an agent can distinguish from get_site_summary or get_site_engagement. However it does not explicitly differentiate itself from siblings beyond referencing get_site_summary's conventions, so it stops short of 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?

It gives concrete when-not guidance: 'Speed is counted by page, so a goal, entry or exit filter rules it out, answered with available: false, why and what to try,' and instructs the agent to read and pass on caveats before reporting. No explicit alternative tool is named, so it is not a full 5.

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