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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds only that the calculation is relative to the mid-market rate; it discloses no additional behavioral traits such as handling of zero/invalid rates or what happens when bank_rate is below market_rate.

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?

Three short sentences, front-loaded with the core purpose and definition of the metric. The trailing pointer to list_bundles for 'voyage' calculators is a marginal cross-sell that does not help invoke this tool, but it costs little.

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 only two required numeric inputs, an output schema present, and annotations covering the safety profile, the description supplies everything needed to call the tool correctly. The only omission is disambiguation from the duplicate-looking sibling.

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 both parameters are already documented (bank_rate = 'Bank/bureau rate', market_rate = 'Mid-market rate'). The description restates them as 'offered rate' and 'mid-market rate' without adding format, unit, or ordering semantics beyond the schema, so the baseline of 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: detecting the margin a money exchanger charges over the mid-market rate, which is clearer than a generic 'calculate margin'. However, it does not distinguish itself from the near-identical sibling calculate_exchange_rate_margin (nor calculate_currency_exchange / calculate_currency_cross_rate), leaving an agent unable to choose between the two.

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?

'Use to compare currency exchange offers' gives an implied context of use, but there are no exclusions and no named alternative — critically, the almost identically named sibling calculate_exchange_rate_margin is never mentioned, so the routing decision is left unresolved.

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