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

Annotations already declare readOnly, idempotent, and closed-world, so the safety profile is covered. The description adds real behavioral detail beyond that: half-up rounding to cents and the fact that extraMonthly reduces principal, which materially affects results. It stops short of explaining how the amortization schedule is shaped, but the output schema carries that.

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?

Three tight sentences with the core purpose front-loaded, then rounding semantics, then the optional parameter's effect. No filler or restatement of the title.

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 needn't explain return values, and annotations cover safety; the remaining essentials (purpose, rounding, extra payment) are stated. Minor gap: no stated rate/term assumptions or error behavior, but nothing critical is missing for correct invocation.

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%, so all four parameters are already documented, giving a baseline of 3. The description tangentially reinforces extraMonthly's effect on principal but adds no syntax or unit detail beyond the schema's own descriptions.

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 (Calculate) plus resource (reducing-balance loan installment and amortization schedule), which is far more precise than the generic 'calculate' siblings like calculate_percentage. An agent can immediately tell what the tool produces without opening the schema.

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 implied by the specialized domain (loan EMI), and no sibling overlaps meaningfully, but there is no explicit when-to-use or when-not-to-use guidance. The description never states assumptions such as fixed-rate or that it is not a general percentage calculator.

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