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

Annotations already declare readOnlyHint=true and idempotentHint=true, covering safety. The description adds that output includes both unit margin and percent of price, but says nothing about edge cases (e.g., zero price) or the underlying formula. This adds some context beyond annotations, so 3.

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?

Description is one short sentence with no filler or redundancy. It front-loads the core purpose and avoids repeating parameter names. Perfectly concise.

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 simple two-parameter calculator with an output schema, this description is mostly complete for an agent to understand return dimensions. However, it omits contextual cues about when this metric is useful or how it relates to sibling tools, and it does not explicitly state the formula. Still, given the simplicity and annotations, it is adequate, scoring 4.

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?

Both parameters have full descriptions in the schema (selling price per unit, variable cost per unit), so schema coverage is 100%. The tool description does not add any additional parameter semantics beyond what the schema already provides. 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?

The description clearly states the tool computes contribution margin per unit and as a percent of price, distinguishing output forms. Though it lacks an explicit verb like 'calculate', the noun phrase is specific and unambiguous. Given sibling tools like break-even-units and margin-markup, the description narrows the scope but does not explicitly differentiate from them, so 4.

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?

No guidance is provided on when to use this tool versus alternatives like margin-markup or break-even-units. The description merely states what it computes, leaving the agent to infer from the name. This is a clear gap for a financial calculator with many siblings.

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