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

Annotations already cover readOnly/idempotent/non-destructive safety, and the description adds substantial behavior beyond them: caveat rules that can change what a figure means, figures counted only from a later day, and the failure mode of returning available: false with why and what to try. That is exactly the kind of operator-relevant behavior annotations cannot express.

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?

Purpose and the key scoping constraint are front-loaded, and nearly every clause carries distinct information (no filler sentences). The trade-off is a dense, semicolon-spliced paragraph that is slower to scan than a structured field-by-field account, but it is not padded.

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 must explain return values — and it does, naming time_on_page's median_seconds/average_seconds/six bands, scroll_depth's average_percent/read_to_end/scrolled shares/first_screen_percent/depths, and previous/change units (whole percentages vs points). Combined with the caveat and failure-mode guidance, an agent has everything needed to call and interpret this tool correctly.

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 100%, so the schema already carries parameter meaning; the baseline is 3. The description only cross-references 'name the site, range and filters as for get_site_summary' and notes the entry/exit/goal filter constraint, which is more usage guidance than new per-parameter semantics.

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+resource+scope: 'How a site's pages were read over a range', anchored to the dashboard's Engagement section, one reading per pageview. It also distinguishes itself from get_site_breakdown ('break ... down by time_on_page or scroll_depth') and get_site_summary ('for bounce rate and visit duration'), so an agent can differentiate without opening schemas.

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?

Explicit routing: use get_site_breakdown for per-page dimension breakdowns and get_site_summary for bounce rate/visit duration, with the conditions that select each. It also states a real exclusion — goal, entry or exit filters rule the call out and return available: false — plus the prerequisite to read the caveats before reporting figures.

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