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

Annotations only declare readOnly/idempotent/closed-world; the description adds substantive behavior the agent could not otherwise know: same-weekday multi-week baseline, drivers split into visitors vs pages-per-visitor, per-source/URL/landing-page/UTM attribution with shares, and explicit reporting of unattributable traffic. It also sets an interpretive contract — correlation is labelled correlation, never causation.

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?

Front-loaded with the core purpose and then builds the methodology in one coherent block; every clause (baseline week, unusualness, driver split, attribution breakdown, attribution limits, correlation caveat) carries distinct information. It is somewhat dense and could be tightened, but nothing is padding.

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?

No output schema exists, so the description must convey what comes back — and it does: comparison against prior same weekdays, a measure of unusualness, driver decomposition, per-dimension share attribution, and explicit no-attribution cases. Combined with annotations covering the safety profile, an agent has everything needed to call and interpret it.

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% and the single 'date' parameter already documents the YYYY-MM-DD format and the site-time-zone default. The description adds only the implicit site-time-zone framing, which the schema states more precisely, so 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?

States a specific verb and resource ('Explain why traffic on one day differed from usual') scoped to the signed-in account's tracked website. It is clearly distinguishable from siblings like get_website_overview (summary metrics) or generate_ai_insight (generic AI narrative) because it names the comparison baseline and decomposition dimensions.

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 trigger condition is clear: use it when you need to explain a single day's deviation from normal traffic. It does not name specific alternatives or state when-not-to-use (e.g. for multi-day or aggregate analysis), leaving that inference to the agent.

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