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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false), and the description adds substantially beyond them: it explains the caveats contract (visitors as visitor-days, a partial today) and instructs the agent to surface caveats that change a figure's meaning. It also discloses the failure mode for unsupported filters, including the available: false shape with 'why' and remediation hints — exactly the kind of extra context annotations cannot carry.

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?

It is a long, dense block, but it is front-loaded (purpose first, then caveats, then parameters, then output shape, then the error case) and each sentence carries distinct information that cannot be dropped — output field names, share units, and the series rule for one- and two-day ranges. Phrasing is strained in places ('The answer's caveats are the rules that apply to its figures'), which costs it a point on readability rather than on waste.

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 carries the full burden of the return contract and does so thoroughly: hours with pageviews/visits/visitors and share as a fraction of 1, weekdays with counts and days, the conditional series for short ranges, and totals/counted_by_hour/coverage. Combined with the caveat and failure-mode explanation, an agent has everything needed to call and report this 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 description coverage is 100%, so the baseline is 3, but the description adds meaning the schema does not: which filter dimensions (goal, entry, exit) are structurally incompatible with an hour-counted metric and what happens when they are supplied. It also delegates range/filter semantics to get_site_summary rather than duplicating them, which keeps the contract consistent.

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 opening sentence names a specific verb and resource — a site's traffic broken out 'by the hour of the day and the day of the week in its own time zone' over a range — which is a distinct breakdown shape an agent can tell apart from get_site_breakdown or get_site_summary without opening a schema. It also pins the time-zone semantics, which matters for interpreting the output.

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 clear context for when to reach for it (hour-of-day / weekday distribution) and names an exclusion: goal, entry and exit filters are incompatible because hours are counted by page, so the tool answers with available: false. It also routes parameter semantics to get_site_summary ('name the site, range and filters as for get_site_summary, which refuses the same things') rather than restating them. What it lacks is an explicit 'use this instead of X' contrast with a sibling such as get_site_breakdown.

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