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

Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered. The description adds genuine context beyond that: the fixed set of 12 US platforms, the fact that default platform options are used (a real limitation), and the returned fields plus calculator links.

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?

A single dense sentence with the ranking scope up front and the return contents trailing. Every clause carries information (platform count, default options, returned metrics, links) and nothing is repeated from the schema.

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, and the description compensates by listing what comes back (fees, payout, profit, margin per platform, calculator and compare links). Combined with annotations covering safety and a fully described input schema, an agent has everything needed to call it 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 schema fully documents price, taxRate, itemCost, shipCost, otherCost and shipCharged. The description adds nothing about these inputs beyond 'for the same sale', 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 with scope: 'Ranks all 12 supported US resale platforms by profit for the same sale.' This clearly contrasts with a single-platform calculator, but it never names calculate_fees, so the sibling differentiation is implied rather than explicit.

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 phrase 'each platform's default options' hints that per-platform option tuning isn't possible here and belongs elsewhere, but the description never states when to use compare_platforms versus calculate_fees or get_fee_changes. Usage is inferable but not spelled out.

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