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

Annotations already provide readOnly and idempotent hints, but the description adds meaningful behavioral details: it notes that 'whole months' are used for recouping closing costs (implying rounding) and that the net saving is only computed when remainingMonths is provided. This conditional behavior goes beyond annotations and helps predict tool output based on input completeness.

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?

The description is a single concise sentence that front-loads the purpose and lists the key outputs. Every phrase contributes meaning (e.g., 'whole months' clarifies calculation detail, 'if remainingMonths given' specifies a condition). No redundancy or filler.

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 an output schema present, the description need not explain return values. It covers the essential inputs and conditional behavior, making it complete for a straightforward calculator tool. Minor gaps like edge cases or negative savings are not mentioned, but these are not critical for basic usage.

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 coverage is 100% with clear descriptions for each parameter. The tool description links parameters to outputs (e.g., 'monthly saving' from currentPayment and newPayment) but does not add significant new semantics beyond what the schema already provides. Baseline 3 is appropriate given high schema coverage.

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 identifies the tool's purpose: computing refinance break-even metrics. It specifically names the outputs (monthly saving, months to recoup closing costs, net saving over remaining term), which distinguishes it from sibling tools like points-breakeven or break-even-units. The scope is well-defined and tied to a specific financial scenario.

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 description implies the use case (refinancing with closing costs, current/new payments) but does not explicitly state when to use this tool versus alternatives like points-breakeven or break-even-units. There is no mention of exclusions or conditions for choosing this tool, though the context is clear enough for basic selection.

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