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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds real value by disclosing that the tool returns three comparison figures rather than a single number, which is important given there is no 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?

Front-loaded with a concrete 8% example that immediately conveys the concept, followed by a compact statement of what is computed. The trailing web-page URL is marginally promotional but the content is tight overall.

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 one-parameter, no-output-schema tool, the description is nearly sufficient: it explains the concept, the computation variants, and implies the return contents. Only the absence of any guidance on when this beats the general compound-interest calculator leaves a small gap.

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% for the single 'rate' parameter, so the schema carries the semantics (annual rate of return in %). The description's 'Enter any rate' adds no format or range detail 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 states a specific computation ('compare the Rule of 72, the Rule of 69.3 and the exact compound-growth answer') plus a worked example, so an agent knows exactly what the tool returns. It hints at differentiation from compound-interest siblings by offering the 'exact' answer alongside the rule approximations, though it never names those siblings.

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?

'Enter any rate to compare...' implies how to invoke it but gives no when-to-use versus alternatives, despite close siblings like compound_interest_calculator, cagr_calculator and future_value_calculator existing. There are no exclusions or routing cues.

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