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

Annotations already declare read-only, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuine behavioral context the annotations do not: there are two distinct outputs, and the second depends on supplying both optional inputs. It does not state rounding or currency assumptions, which is a minor residual gap.

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 sentence with zero filler, front-loading the primary result before the secondary one. No redundant restatement of the tool name or the annotation flags.

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?

For a four-parameter, pure-computation tool with no output schema and full annotation coverage, the description is nearly sufficient: it explains what is computed and makes the conditional nature of the second result clear. Only rounding/currency conventions are left unstated.

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 all four parameters are already documented in the schema. The description restates the roles of price, discount_percent, unit_cost and units, adding only the relationship 'to keep the same profit'; it gives no units, precision, or validation guidance beyond the schema's minimum/maximum constraints.

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: computes sale price after a percentage discount, plus an optional extra-units-to-hold-profit result. The profit-preservation half distinguishes it from a plain percentage calculator, but it never names a sibling tool to route against.

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: the phrase 'given unit cost and units normally sold' tells the agent when the second output becomes available. There is no explicit when-to-use, when-not-to-use, or pointer to percentage_calculator / break_even_calculator as alternatives, which matters given 20 calculator siblings.

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