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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is clear. The description adds the key behavioral detail that each cashflow is discounted at the per-period rate, which is not covered by annotations or schema. This goes beyond the basic structure, though it does not elaborate on return behavior, which is acceptable given the output schema.

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 sentence that immediately names the tool's purpose and its key differentiator from a sibling. It is concise, front-loaded, and contains no redundant or unnecessary content.

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 straightforward calculation tool with a complete input schema, an output schema, and annotations covering read-only and idempotent behavior, the description provides sufficient context. It also names the alternative tool. No critical gaps remain.

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% with clear descriptions for ratePct, cashflows, and initialCost. The tool description does not add significant parameter-level meaning beyond the schema, but it indirectly aligns 'ratePct' with the 'per-period rate' mentioned. Baseline 3 is appropriate given the 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 states that the tool calculates the discounted payback period and explicitly distinguishes it from the sibling tool 'payback-period' by noting that each cashflow is discounted at a per-period rate. This provides a specific verb, resource, and key differentiator.

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 phrase 'like payback-period but...' directly references an alternative tool and specifies the difference, telling the user when to choose this tool (when discounting is needed) versus payback-period. This is explicit usage guidance with an alternative named.

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