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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false), so the bar is lower. The description still adds genuine non-obvious behavior: a SKU with no saved cost is counted at zero cost, which flatters profit. That is a material interpretation caveat not derivable from annotations or schema.

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?

Two sentences, front-loaded with the resource definition before the call-condition. The second sentence is long but each clause earns its place by explaining the zero-cost distortion. Minor density of clauses in sentence two keeps it from a 5.

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 carries the burden of describing returns, and it does list the fields. The gap is granularity and volume: it does not say whether rows are per SKU per marketplace per validity window or how many records come back, which 'validity dates' only hints at.

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?

Zero parameters, so the baseline is 4. The field list (SKU, marketplace, unit cost, currency, validity dates) describes the shape of the data rather than arguments, which is appropriate and adds orientation without over-specifying nonexistent inputs.

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 gives a specific resource (product costs / COGS saved in the workspace) and enumerates the returned fields: SKU, marketplace, unit cost, currency, validity dates. It is clearly distinct from the profit-computing siblings like get_profit_by_sku and get_profit_summary, though it never names those siblings outright.

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 states a concrete trigger condition: 'Call this when a profit answer depends on whether costs are actually recorded.' That is real when-to-use guidance rather than generic filler, but there is no explicit when-not and no named alternative tool for the case where the agent wants computed profit instead of raw cost data.

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