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

Annotations already carry readOnly/idempotent/non-destructive, so safety is covered; the description adds genuinely new behavioral context: the cost model ("Free; each connected Google Ads account costs one Google Ads operation") and the fact that it computes a discrepancy between ad-reported and site-observed numbers. It says nothing about freshness/latency or how gaps are computed.

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 scope enumeration comes first, then the routing guidance ("Start here..."), then cost, which is good front-loading and no filler. The first sentence is long and comma-dense with vendors, which costs some readability.

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, the description should carry the burden of telling an agent what comes back; listing the covered sources and the ad-vs-site gap does that at a high level, but it never indicates the shape of the response or whether all connected sources always appear.

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 schema already documents YYYY-MM-DD formats, enum presets and the since/until-vs-date_preset tradeoff. The phrase "One period across everything" weakly reinforces that a single period applies to all sources, but adds little beyond structured data, 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?

The description names the specific aggregation it performs (spend, clicks and results across Meta, Google, TikTok, Microsoft and LinkedIn plus GA visits/key events and Search Console clicks, with gap analysis) rather than restating the title. It does not, however, distinguish itself from siblings 'performance_dashboard' or 'revenue_report', which plausibly overlap.

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?

"Start here when the question is 'where did the money go and what came of it'" gives an explicit entry-point trigger. It stops short of naming when NOT to use it (e.g. single-channel or revenue-specific questions that the sibling reports cover).

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