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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: organic sales are DERIVED (ordered sales − ad-attributed sales) and labelled, which prevents an agent from misreading the figure as a raw source metric.

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 definition, then the comparison, then the trigger questions, then the derivation caveat. Dense but each clause carries information; the em-dash definition is slightly heavy but nothing is filler.

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 must convey the return shape, and it does: totals and per-SKU, ACoS alongside, and each SKU's ad-claimed sales share. The derivation note completes the picture; only pagination/sort behavior is unstated, which is minor.

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 days (7-90, default 30), account and marketplace_id are already documented. The description's 'same store days' phrasing loosely echoes the window but adds no syntax or constraint detail beyond the schema, 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 the specific metric (TACoS = ad spend ÷ all ordered sales) with its exact denominator, and explicitly contrasts it with ACoS and the ad-attributed share. This distinguishes it from siblings like get_ads_arm_economics or get_profit_by_sku without needing the schema.

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?

Gives concrete trigger questions ('what is my TACoS', 'how dependent am I on ads', 'are my organic sales growing') that map cleanly onto this tool rather than its siblings. It lacks explicit exclusions or a named alternative, but the usage context is unambiguous.

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