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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds nothing beyond restating inputs — notably it does not say whether the result is rounded up to whole units or how the per-month framing interacts with the fixed_costs input, which is the one behavior an agent would want to know.

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 front-loaded sentence with the output stated first and the inputs after; nothing is redundant. The phrasing 'from fixed monthly costs, price, cost per unit and payment fee percent' is slightly listy but earns its place by mapping to the four parameters.

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, so the description does carry some burden for the return value — it does say it yields 'how many sales a month,' which is adequate. Missing are rounding behavior and how the payment fee is netted against price, both of which matter for interpreting the result.

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% and every parameter is documented there with units and defaults (payment_fee_percent default 0). The description merely lists the same inputs in prose and adds no format, unit, or edge-case semantics 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?

Names the specific computation (units sold per month to cover fixed costs) and the inputs driving it, so an agent can tell it apart from sibling calculators like profit_margin_calculator or roi_calculator. It stops short of an explicit contrast with those siblings, but the verb+resource+output is clear.

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?

Usage is only implied by the nature of a break-even calculation; there is no statement of when to prefer this over profit_margin_calculator or hourly_rate_calculator, nor any prerequisite. For a self-evident arithmetic tool this is minimum viable, not misleading.

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